Export Impact For Good

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    HS.P.1.1. - History of hides and skins

    Short story on hides and skins production
    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 9:55:58 AM

    Prehistoric men hunted wild animals

    Throughout the history of mankind hides and skins have been an important part of each day's life. Prehistoric men hunted wild animals for their food and used the hides and skins they retrieved from the killed carcasses to cover themselves from the cold and to protect their feet.

    Some tribes used hides and skins to build their homes. There was already a distinct notion to "process" hides. There is proof that hides and skins were fleshed with tools. Even today many tribes all over the world follow the same prehistoric pattern.

    Some tribes used hides and skins to build their homes

    Modern men raise animals to provide for their food and use the by-products for a variety of purposes. Practically nothing is thrown away or wasted. The hides and skins, one of the many by-products of the meat processing operation, are collected and treated for conservation. Apart from being an economical windfall, collection of hides and skins is a necessity, because otherwise they would become a serious environmental threat. Hides and skins mainly consist of water and protein, which like all protein products putrefies if not properly treated. Burying or burning hides and skins is not an option because of the huge quantity that is daily produced. Why should one destroy hides and skins anyway considering the fact that they have a great economical and social value. In fact in many developing countries with few natural resources, the production and export of hides and skins is an important foreign exchange earner. The better the quality of the hide and skin, the better the price that can be fetched on the international market.

    HS.P.1.2 - The raw material

    The raw material
    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 14/03/2007 2:46:42 PM


    Contrarily to other commodities, hides and skins are produced everywhere, in each village, town or metropolis, in each and every country, all over the world, without exclusion. Each continent and all seas and oceans produce hides and skins. Where there are people, independent from race, religion or political association, there is a production of hides and skins. There isn't a type of animal in the world, that doesn't or hasn't provided the basic material for the production of leather. The list is far to long to report, but generically speaking mammals like bovines, goat, sheep, any sort of wildlife, reptiles, fish and birds, all provide us with a hide or skin, that can be processed into leather. Each area has its own typical breed of animals, which goes hand in hand with the local climate and habitat. Hides and skins are structurally different when originating from hot or cold, from dry or humid climates. Generally speaking healthy animals provide for good quality hides or skins, whereas animals from dry areas with little food produce low quality hides and skins. Animals that are well fed produce thicker and better hides than their brothers or sisters that are just able to survive. Each production area is characterised also by its environment and by the local laws or habits. Dry bushy areas with lots of insects will provide for skins with scratch and insect bite scars. Countries where cattle or small ruminants are kept apart by barbed wire will produce hides and skins with scars from wounds caused by the barbed wire. Hides and skins from life stock that has been treated with pharmaceuticals against illnesses and parasites are better than hides from life stock that is untreated. Hides from fallen animals that have died from natural causes and hence have not been bled, are different from hides that have been produced by slaughter, because in a fallen animal the blood remains in the veins whereas in slaughtered animals the veins are practically void of blood.


    If hides within one country but from different areas distinguish one from another, it is obvious that hides from different continents and different climates have significant differences. It is virtually impossible to list all the characteristics of each origin and thus a table that highlights the differences between origins is impossible to develop. However to give an example we can summarily and very generally compare a wetsalted cattle hide from the US east coast with a wetsalted hide from a bovine of the same age, let us say 2 years old, from Bangladesh.

    United States




    No hump





    Thick hide


    Thin hide

    Insect/parasite protection


    Few scars


    Many scars

    Average weight

    20 kgs

    15 kgs


    Coarse grain

    Fine grain



    Not so good

    Flaying marks and holes


    Machine flay


    Hand flay

    Fibre structure



    Brand marks


    Unlikely or few


    The large majority of hides and skins that enter the market for transformation into leather originate from slaughter animals that provide for meat, and hence their hide or skin is a by-product of the meat industry. The percentage of leather produced from certain mammals, marsupials, reptiles and from fur animals (with the exception of sheep), whose skins are the main product and the meat the by-product, is relatively very small, up to the tune of a few percentage points of the worldwide leather output. Over the years some positions have dramatically changed. Kangaroos were killed by farmers in Australia, because they destroyed crops and the skin was buried together with the carcass or was just a way to make a few dollars. Today kangaroos are culled in a predetermined number of head per year with licenses issued by the Australian government. The skins are professionally sold for leather production and the meat is exported to Europe or transformed into pet food, or. Ostriches were killed in the past exclusively for their skins and feathers, whereas presently ostrich meat is served for human consumption worldwide as a delicacy. Likewise crocodiles and alligators were merely killed for their skin, whereas now game restaurants serve croc or alligator meat.
    Each type of hide and skin has its own peculiarities because of size, weight, thickness and grain characteristics which distinguishes each category one from the other. Just by looking at the grain you can tell a bovine from a buffalo, a goat, a sheep, a kangaroo, a pig, a horse, a camel, a deer, a fish etc.













    Decorative hides and skins distinguish themselves one from another by the type of hair or wool, and the pattern and colour scheme of the hair or wool.

    Cattle hide




    The international contracts quoted in paragraph M6 specifically state that a seller does not guarantee whether purchased hides and skins are suitable for a specific purpose. A buyer however buys a particular hide or skins because of its known characteristics which he considers suitable for the product he wishes to transform the raw material into. Each and every type of raw material can be used in general for each and every purpose. One type of raw material can be more suitable than another for a specific end product, but in principle restrictions are extremely few. In the past this was different, but technology and chemistry have evened the field.


    When in the past the market was Europe-centred, currently the market is focussing on the Indian subcontinent and in particular on the Far East, with the People's Republic of China as the front runner.
    There is a division in the market with Europe leading for the purchase and transformation of high quality raw Materials, and the remaining markets concentrating on low and medium quality raw material.


          Import 1988

        Export 1988

         Import 2003

           Export 2003

    Latin America















    Near East





    Far East





    P.R. of China





    North America




















    Former USSR





    (source FAO World Statistical Compendium for raw hides and skins 2005)

    From the table above one can see the quantities of raw wetsalted bovine hides and skins (calf) that have been imported and exported in a number of countries and continents. The difference between 1988 and 2003 both in imports and exports indicates the trend of the manufacturing sites of leather. 
    The table below actually gives the relative percentages and one can note, that in 1988 Latin America exported 72.74% raw hides less than it imported. In 2003 Latin America exported 47.69% less than it imported, hence the export of raw hides has increased percentage wise. In 2003 Latin America imported 32.65% more hides than in 1988, but it exported 154.55% more hides and skins than in 1988. Kenya exported 600% of raw hides more in 1988 than it imported in the same year. In 2003 it exported 2150% more than it imported. Considering that Kenya produced in 1988 25.200 tons, and in 2003 it produces 27.800 tons of wetsalted hides and skins this means that the local tanneries have less raw hides available for processing than in 1988. Similar imbalances are found all over the board except for the Far East where China imported in 2003 307.59% more hides than in 1988 and it exported 2.68% less hides in 2003 than in 1988. If one takes a closer and more detailed look at these figures offered by FAO, one can deduct that the trend is, that the processing of hides and skins is shifting to the Far East and to the People's Republic of China in particular.  

    Percentages can be found in the following table:


    Imbalance Exp/Imp 1988

    Exp/Imp 2003

    Imbalance Imp.1988-2003

    Imbalance Exp. 1988-2003

    Latin America















    Near East





    Far East





    P.R. of China





    North America




















    Former USSR





    In the first decade of the 21st century the trend will be that mass produced leathers of low and average quality in simple basic colours will be produced in newly emerged countries like China, India, Pakistan. Sophisticated high quality leathers specifically aimed at the high fashion market will be produced in Europe and particularly in Italy. Upholstery leathers will probably be produced mainly in South Africa and South America. Most probably North Africa will emerge as competitors for the tanning industry in the Indian subcontinent, whereas the Sub Saharan tanning industry will continue to suffer from the unavailability of raw materials, which will continue to be exported towards the Far East rather than being processed in the countries of origin.
    In the long term one can envision that the big industrial flight in the tanning industry from the developed countries towards the Far East will slow down and stop, and maybe partly reverse until a natural balance is found. At the same time there may be a blossoming of the Sub Saharan tanning industry fulfilling a necessity of cheap unsophisticated leathers which neither the developed countries nor China will be able to produce at competitive prices.

    World Supply of hides and skins
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 14/03/2007 10:30:28 AM

    The hide and skin are only by-products of meat industry. The market prices are submitted to rapid and large fluctuations due to changes in the international economic picture. In general, the raw hide represents 50-60% of the cost of finished leather. For this reason, such fluctuations are of prime importance in the economics of running a tannery.  

    The recent statics concerning raw hides available worldwide (actual slaughtering and collection of hides for marketing) yield the following averages: 

    - 272 milions cattle hides (cow, calf , buffalo). Average 40 sq.ft area yield  
    - 386 milions sheepskins. Average 6 sq. ft. area yield  
    - 144 milions goatskins. Average 5 sq.ft. area yield

    The developing countries are increasing the live-stocks due to the improvements in animal husbandry, provoked by demands from meat industry or by improvements in methods of feeding, cure and collection.

    On a world scale, significant cattle populations are to be found in the USA, Argentina, Brasil, the former USSR and the EU. Sheepskins originate predominantly in New Zealand, Australia, the Near East and the EU. The main centres for raw skin production do not coincide with the major leather production centres, thus indicating the necessity of proper storage and means of transport. Typically hides and skins are traded in the salted state, or increasingly as intermediate products, particularly in the wet-blue condition for bovine hides and the pickled condition for ovine skins.

    Within developing countries, exports from Latin America and Africa have fallen, while those of the Near East and the Far East have increased. For sheepskins, Oceania remains the dominant exporting region.

    The tendency for bovine hides and skins is that developing countries change from being a net exporter to being a net importer, reflecting an expansion in tanning capacity in most developing countries, especially in the Far East and in Latin America. Conversely, the role of developed countries has changed from that of a net importer to net exporter of cattle hides. Japan and Western Europe are still net importers.

    The european tanneries import wet blue from a wide range of sources: the USA, Argentina, Brazil, South Africa, Australia, Russia and Eastern Europe.

    This means that certain steps of the processes of integrated tanneries are transferred to other countries, particularly to third World countries. From the environmental point of view this development has two consequences. First, environmentally important steps are transferred to other countries, and secondly, particular agents, which are restricted or prohibited within the EC, might be applied and are consequently imported via the hides and skins into the EC. As regards sheepskins, developing countries became net importers in the mid-nineties. Conversely, the developed countries as a whole are net exporters; Europe again, though, remains a net importer.

    Types and origin of hides and skins
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 14/03/2007 10:35:11 AM

    In the terminology of leather industry, the skins of large animal, such as cattle and horses, are called hides whilst the term skins is used for the small animals, such as sheep, goats and calves. The term "hide" is never used for the small animals Hides and skins differ in their structure, depending upon the habits of life of the animal, season of year, age, sex, feeding and breeding.. The skins of young animal, are smaller compared with older ones, the grain pattern is fine and smooth; often the skin of young animal has less damage by diseases, insects, stratches. The quality is better when the feeding and living conditions are natural. Some characteristics of skin depend on the sex of the animal. In fact the female skin presents a finer pattern grain than the male of the same breed, whilst its fibre structure is looser, particularly in the flanks. Consequently, the leather is softer and shows loose grain.
    The skin with less hair gives a stronger leather in comparison with that one with more hair.

    1. Cattle hides

    In this family are included bulls, cows, oxen, veals and calves. The bulls and the cows are respectively full-grown male and female. Their hides are large and the weighing goes from 16 kg to 37 kg, bull hides may weigh more. The hides of Veals come from younger animals and weigh 6,5-11,5 kg. The skins of calves come from young animal and the weighing goes from 2,5 to 5,5 kg. The main difference between calfskins and cattle hides, from a structural point of wiew, is the fineness of grain. Calfkins have a very fine structure as compared to cattle hides and are usefull for the finest of leathers.
    The hides of Zebu or Brama, that is a humped-backed ox, are relatively small and come from India. They are called kips and their weighing goes from 9 to 15,5 kg . Their structure is open and a thin and soft leather results. A great quantity is sold in vegetable or half-tanneed state or in wet blue.
    North America produces all types of beef and dairy hides. These hide, that come from the meat packing stations, are sorted and carefully cured by wet salting or brining South America produces hides, called frigorificos. They come from a large meat packing industry marketing and are similar to wet-salted or brined packers hides. Saladeras come from large slaughter-houses. They can vary in quality of flay and cure. Mataderos come from town slaughter-houses. The quality of mataderos is inferior to saladeras. The flesh side is full of cuts provokated by flaying operation, the uniformity of breed and cure is not saisfactory. The term Campos indicates hides flayed and cured on the farm-houses. Generally, these hides are salted. The quality of flaying and cure is not satisfactory. The amount of wet blue or crust sold by Brazil in the last ten years is strongly increased.
    In Africa, the hides are smaller and dried. In Nigeria as well as in Tanzania, hides, generally, are dry-salted.
    The hides coming from Australia and New Zealand are wet-salted or brined. France, Germany, Italy, Switzerland and Scandinavia there are high quality wet-salted hides.

    2. Buffalo hides

    Generally, the hides are thicker and wrinkled on the shoulder. They have a coarse grain whilst the fiber structure is loosened. The hides are exported from India, Pakistan, Nepal and Indonesia in dried or vegetable- tanned or in wet blue state.

    3. Sheep skins

    The sheepskins show different characteristics depending on the breed. Generally, the square feet of the skins employed in tannery, can go from 5,5 to 8,5. Australian Merino is known for the quality of wool. Unlike his wool, the quality of skin is very bad because it contains a large grease amount and the fiber structure is weak. Merino' skins present ribness on the grain. The skins are exported in Europe for fellmongering.
    The english sheepskins, called Domestic, have a fine grain. The fiber structure is compact. These skins, suitable for garment leather, are exported in pickled state.
    New Zealand sheepskins do not present the typical defects of Merino breed. They are suitable for garment leather. These skins are exported in the pickled state.
    The sheepskins from Middle East (Syria, Lebanon, Iran, Saudi Arabia, ecc.) are suitable for garment and glove leathers. In fact, these skins have a strong structure, fine grain and contain less fat. They are exported in the pickled conditions.
    The sheepskins from South-Africa, known as glovers, are exported in pickled conditions. They are suitable for high quality garment leather. The grain pattern is fine and the structure is compact and strong.
    In Nigeria there are especially cross-bred skins. The skin structure is suitable for shoe leather, being strong. The grain structure is fine and the fat content is much low. These skins are exported in wet blue state.
    Dressing sheepskins are those destined to be tanned with wool on. In this case, the wool fineness and density play a role wery important.

    4. Goatskins

    Goatskins, as compared to sheepskins, have a very tight fiber styructure and are easily recognized . They show a characteristic grain pattern. The structure od goatskins allow its use in the more durable type applications in the manufacture of gloves and shoes. The goatskins are imported from India, Pakistan, East and West Africa, South Europe, South America.
    The goatskins, called Madras, are imported from India in vegetable-tanned conditions, whilst from Nigeria, Ethiopia, India, Pakistan can be imported in wet blue conditions.
    The skins coming from East Africa, frequently, present grain damage. For this reason they are suitable for the production of suede; especially, the skins coming from Ethiopia are indicated for this article.

    5. Horse Hides

    Horse hide may be divided in two parts that differ each other for the fiber structure. The foreward part of the hide is relatively light skin and the texture of this area is not much different from some types of goatskin. The fore-part of the hide is used for gloving and shoe upper leather. The back portion of the hide, from the rump, contains a much thicker, less porous area, known as the crup, that is usually cut out. It is the source of Cordovan leather. Substantially, horse hides comes from Holland, France, Belgium, UK and Scandinavia.

    6. Pigskins

    Pigskins show an unmistakable grain pattern. The hair penetrates deeply through the grain layer and leaves holes in it. Peccaryskin is a particular type of smaller pigskin, that gives a grained soft leather for gloves. The English and U.S.A. pigs give larger and much fatter skins. The most consistent quantity of pigskins comes from China, the former U.S.S.R, U.S.A, Middle Europe, Japan. Pigskins are destinated, usually for suede garment, lining and bags. 

    7. Reptile Skins

    Reptiles skins do not have the hair and epidermis but a keratinous layer of scales, that is eliminated by unhairing operation. Many types of lizards come from India and Indonesia. Other types originate from Africa and South America. Generally, these skins are dried. The dried raw material is not easy to soak.
    The crocodile skins come prinicipally from Africa and Far East. There are two types of crocodile: large and small scale. The small scale are more valuable.

    HS.P.1.3. - Flaying

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:03:46 AM

    In some cases skins are part of the food chain, and people actually eat hides or skins. In Indonesia people eat pre-processed hides as krupuk. In Ghana people eat dried camel hides and in Mexico fried pork skin is a local delicacy. In general however they are recovered from the slaughtered animal for purposes other than food. After the animal is killed the first operation is to remove the hide or skin. This is called hot flaying, because the carcass is still warm. This has both practical and hygienic reasons, even if in the USA many carcasses are left unskinned when they have to travel over large distances in refrigerated railway wagons to places where the value of the meat is higher than in other places. Removal of the hide in this case is called cold flaying. Cold flaying requires more force and normally damages the hide or skin, or at best interferes with the fibre structure of the hides. Flaying should be done as well as possible. Holes or deep cuts from flaying knifes reduce the value of a hide or skin, hence in order to obtain the highest possible value for a hide or a skin, the flaying should be done with care.


    Slaughter methods and situations are closely related to the flaying operation and subsequently the quality of the hide. Depending on the slaughter method one can obtain a higher or lower quality of flaying. There is a distinct difference between slaughter in an organised abattoir and a rural slaughter slab. Much depends on government dispositions, that regulate slaughter mainly for hygienic and public health reasons. Some countries have very strict laws that regulate meat production, others have no laws at all and allow even backyard unsupervised slaughter. Without exception well regulated slaughter provides for better flay quality in hides and skins. Unregulated slaughter provides as a fist rule bad flay quality. Good flay quality goes hand in hand with well regulated hygienic slaughter operations. When a community produces good quality meat, it almost automatically produces also better flay quality for their hides and skins.


    Before mechanisation all flaying was done by hand. The removal of the hide or skin is an operation that is ruled in many areas by tradition. In many countries small skins are pulled by hand from a hanging carcass, resulting in a skin that presents itself as a sort of tube, which you can compare to a coverall. Pulling a skin by hand produces a rather good quality flay.

    With large animals or small animals (calf) whose skin is particularly firmly attached to the meat this sort of flaying is not possible, and one has to resort to flaying with the assistance of a knife. The knife is both a useful and a dangerous tool. If a flayer gives little attention to what he is doing, he can easily cause damage to the hide or skin by making cuts or even holes. Each bad cut and each hole reduces the value of a hide. Hides and skins with more than 10 deep cuts and/or holes fetch such a low price, if there is a demand at all, that it becomes economically unfeasible to collect such material, and it becomes then a total loss.

    In order to make hand flaying a bit less risky, special flaying knives have been designed with a round rather than a pointed edge, but unless used with a certain circumscription and professionalism, also these particular knives do not guarantee a better flay quality.

    Hand flaying is done simply by detaching the hide with a knife from the fat or meat of the carcass. The less fat or meat is attached to the hide or skin, the better it is for the butcher who sells the meat as it is obvious that the price per kilo of a hide is far less than that of the meat. The closer the flaying knife is held to the hide, the more likable it becomes that flay damage is done to the hide. Exception is made for game, fur, reptile and other exotic hides and skins, where the hide is the main product and the meat the by-product.

    A typical hand flay operation of a goat or sheep takes about 5 minutes, whereas for large cattle a hand flay operation takes somewhere between 10 and 15 minutes. Speed in flaying compares inverse with flay quality. The slower the flaying operation is executed, the better is the quality, and hypothetically the higher is the price that can be fetched for the hide. In abattoirs that process a substantial quantity of cattle but not enough to warrant a mechanical hide puller, hand flaying can be done with specially designed knifes (Jarvis knifes) that vibrate and thus do not easily cause cuts or holes if properly operated.


    In large abattoirs machine flaying has taken over from hand flaying. Machine flaying is enormously faster and at the same time gives an almost perfect flay quality, causing less fatigue. Machine flaying refers to the most important part of a hide, the butt. Bellies and legs must be opened by knife, hence for a good flay quality the flayer must pay attention to his job.

    The big drawback of machine flaying is that the machine costs a large amount of money, and needs some sort of power supply and is subject to continuous maintenance. These factors are of little relevance for a large city abattoir, but become an impossible hurdle for a small abattoir with a low production. An abattoir that produces less than 100 head of cattle per day rarely commits capital to buy such a machine.
    There are several flay machines available, from rather basic to very sophisticated running from Us$ 15'000 to Us$ 25'000 and more. All produce hides without cuts or holes and take about one minute to pull a hide from a carcass. The operation is executed in a rather brutal way because the hide is pulled from the  carcass using the weakest link between hide and carcass namely the fat. Some fat remains on the hide, some on the meat. Some meat will also remain attached to the hide and in order to reduce the quantity of meat staying on the hide one has either to hand-assist the flaying or by means of a Jarvis knife. In developing areas the meat that remains on the hide is subject to manual fleshing (see P1.1.6), which unfortunately causes cuts to otherwise perfect hides.


    When a small abattoir or slaughter slab wishes to produce good quality hides, but cannot install for production and economical reasons a mechanical hide puller, there is a way in between. There are several low cost methods and devices that allow hides to be pulled, one as low as Us$ 100/150.= and apart from being cheap it can be made anywhere where there is (scrap) iron and where welders are available. The principle of these devices is the same as the principle of the mechanical hide pullers, with the difference that the cost of these devices is much lower. The end result of the flaying quality of these devices is the same as the results obtained with mechanical hide pullers. If the device is used in a proper way, it can and will produce a perfect machine flayed hide without cuts or holes with great speed and little effort.

    Some devices are more sophisticated than others. Some need maintenance, others don't. Some need power, others require only mechanical means like a pulley block. The pulley block is the costliest piece of equipment for this flay device. Its cost varies from country to country, but lies around 250 dollars. Experience has shown that cheap pulley blocks wear easily, whereas sturdier more expensive blocks last far longer.

    The very existence of these devices means that virtually all abattoirs and slaughter slabs can produce good quality hides. It is a matter of will, organisation and basic entrepreneur talent. The SFF ©, Static Flaying Frame©, shown above has been backed by several EU and UN institutions amongst which the International Trade Centre, who presented the SFF©  with the collaboration of other institutions for the first time at the Tunis Meet in Africa in 2002. A number of SFF© have been placed in a several developing countries as pilot projects and the frame has demonstrated its validity and its capability to provide for machine flay quality hides. Further information about the SFF© can be obtained from the International trade Centre and from: www.limeblast.org 


    Whatever the method used, hand flaying or hand assisted machine flaying, there is a choice whether to perform the operation, or part of it, with the carcass lying on the ground, or with the carcass hanging vertically from a hook or rail.

    Experience and logic show that when a carcass is lying on the floor of a slaughter house or slaughter slab, the quality of the flaying is lower than when the flaying operation is executed on a hanging carcass. The flaying job on a hanging carcass is done easier, faster and with less fatigue. The fringe benefit of working on a hanging carcass is also improved hygiene and better food safety to the benefit of public health.


    Whether a hide is removed by hand or machine, there will always remain some meat and fat on the hide. On an average this accounts for an estimated 20% of the green hide, and is undesired by the tanning industry.

    Removing the fat and flesh before salting ensures that this sub product, free of salt or other conserving agents, can be sold to other industries, like the cosmetic or food industry. A properly green fleshed hide allows furthermore for better and faster curing. Fleshing of green hides should be done immediately after flaying. The operation requires a suitable fleshing machine.  

    In developing countries the (unprofessional) fleshing of hides and skins after flaying constitutes a major value reducing factor. Fat and fleshings are edible products with a relatively high commercial value. This means that after flaying unskilled workers descend on a hide to remove the meat and fat. The more weight they remove from the hide, including pieces of hide, the more money they get for recovered product. The faster they work the earlier they can get their pay. As a result a perfectly flayed hide can lose its premium value due to sloppy fleshing. As a matter of  fact the great majority of machine flayed hides are ruined when submitted to hand fleshing in developing countries, dramatically reducing the value of the hide and neutralising the beneficial effect of careful flaying. Abattoirs or the owners of the hide in general unfortunately don't pay attention to this very important phenomenon. If the fleshing cannot be avoided in order not to deprive people from making a living, then at least a proper workplace should be provided. This consists of a flat cement floor, which avoids that while fleshing the knife encounters an obstacle causing a cut.

    Flaying and Trimming
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 10:04:16 AM


    After the slaughtering, the  blood must be removed from the carcass and from the small arteries and veins of the skin, otherwise it clots therein. In this case, putrefaction takes place quickly; consequently blue-black markings and areas of putrefaction will form in these regions. To this end, the beast is hung up by the hind legs on the transporter rail.

    The flaying could be carried out whilst the carcass is still warm. In this case the hide loses the body heat more quickly. The quicker wasting of body heat reduces the possibility of putrefaction.
    The hide of a fallen animal is especially affected by blood because the blood congeals after its death. 

    The animal is hung up by the hind shanks. Hide is flayed by making ripping cuts only with a pointed knife. The legs are severed at the knee joint and the ripping cut should be up the inside of the leg. The hide is peeled away from the belly rip line with the aid of round-bladed knives, in order to minimize the cutting in the belly areas. The legs are then flayed. The use of the knife must be limited as little as possible.  For this aim, machines are available, which grip the edges of the skin and pull it away from the carcass.
    For smaller animals, the removal of the skins can be obtained by blowing of compressed air between skin and carcass through a small hole made in the hind shank. After the flaying operation, the hide is removed immediately and washed with cold water in order to eliminate dirt, blood, bacteria that constitute a potential source of putrefaction.

    Generally, developing countries carry out manual flaying and many cuts are produced in the skin. The cuts reduce strongly the value of the leather and split. Cuts pierce or go halfway or more through the hide. In many cases, the cuts can reach the grain side of leather and produce holes that depreciate deeply the value of finished leather. More frequently, knife cuts that do not go halway through the hide, are deep enough to cause damage in the finished leather. 

    A correct flaying system allows to achieve the hide or skin that presents a regular square shape. That depends on the right location of the ripping cuts and adequate trimming. In the past, it was common for a tanner to find even weight-adding components such as hooves, horns. 


    The tanner then trimmed of these parts before starting his process. The economic loss from the old trim practice is obvious. As a result of the cooperation between the farmers, packers and brokers through their respective associations, the American Tanners Council was able to define a new trim system which has become the standard of the tanning industry. The modern hide trim results in a higher price per kg for the tanner but a net economic gain in the saving of freight.   

    Modern Trim Diagram

    HS.P.1.4. - Preserving

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:09:03 AM

    After slaughter the hide becomes a perishable commodity.  Time and temperature are crucial factors. Green hides and skins should be treated for proper conservation within a couple of hours from slaughter. This period can be longer in cold climates (< 20°C) and shorter in hot humid climates. The picture on the left clearly shows a freshly slaughtered skin (right) and a skin (left) that was left without treatment for a couple of hours in the sun. Apart from bacterial action a hide or skin can consume itself in a process called autolysis, which reduces the hide to gelatine.

    One sees in many abattoirs that after flaying the hides are dropped in some corner in water and blood until the slaughter operation is completely finished and the hide merchant comes to pick up his hides. This careless treatment of the hides accelerates the deterioration process and should be avoided. Hides and skins must be kept out of the sun, whether fresh or during salting or drying. The conservation treatment should start immediately by storing the hides temporarily in a safe place where there is no risk of water or blood contamination. Fresh hides should not be piled. Due to piling before chilling fresh hides can reach quickly high temperatures (40-45°C) that provoke a damaging bacterial action within a relatively short time after slaughter. There are two major methods of preservation. By drying, dehydration, or by salting. There are abattoirs in the People's Republic of China that freeze their hides, but this is a rather uncommon method.


    The cheapest method of conservation is by dehydrating the hide as fast and as gradually as possible after slaughter before the process of deterioration takes hold of the hide or skin. It is wrong to dry a hide or skin in the sun or on the ground. In the sun a hide or skin more or less cooks in its own fat, and the ground retains the humidity that evaporates from the hide and delays complete dehydration, or worse, the ground can be humid and can transfer the humidity to the hide or skin. Ground drying delays the process and causes bad conservation quality. Skins can be dried on drying lines or poles, hides cannot because where the two sides of the drying hide face each other, humidity evaporates too slowly. Ideal is suspension drying where a hide or skin is suspended under tension in a frame. This increases the evaporation surface and the tension opens the fibres of the hides allowing faster dehydration.

    Hides should be suspended tails up, necks down. The butt is the most valuable part of a hide and by keeping the butt up gravity helps the water in the butt to descend first rather than collecting the descending water from the shoulder portion. Normally a goatskin dries in a warm ventilated climate within 24 hours, a sheepskin in 36 hours and a hide in 3 days. It is recommended that hides and skins should be bone dry before they are taken off the frame.Frames should be built in rows one parallel to the other with sufficient room for workers to pas between them.

    The positioning of the frames should be such, that they are parallel to the prevailing wind direction. Wind should be allowed to stream easily between the hides as it blows away the humidity that is created by the evaporation process facilitating faster dehydration. Frames should be shielded from the sun and rain under a roof. In countries with a clear distinction between the dry and wet season will have generally a better hide quality in the dry season and a lower quality in the wet season. The slower hides and skins dry the bigger the chance for conservation defects in the form of putrefaction. It is absolutely imperative that dried or drying hides and skins are not exposed to water!


    Salting is a safer method of conservation than drying, but it is costlier because you need to buy salt which in a landlocked country without salt mines doesn't come cheap. The European Union requires 2% of sodium carbonate to be mixed in the salt. Other additives like naphthalene with boric acid and sodium fluoride are used, but each have their draw-backs.

    Freshly flayed hides should be salted within a couple of hours from flaying. The hides should be as clean as possible, but it is not necessary to wash them. The salting room should be ventilated, but not excessively so as drying should be avoided. If possible the floor of a salting room should be made on purpose. The areas where a stack of hides is salted should be slightly bulging in order to allow water that evacuates the hide to drain. This avoids the hide that touches the floor from lying in the salt water. Alternatively hides should be laid on pallets for salting. A fist rule says that about a third of a hides' weight should be the quantity of salt used. The forming of water poodles on a hide is to be avoided.

    Salting is done on a well spread hide carefully avoiding folds to form. Hair down, flesh up. Once a hide is well spread it should be covered with a layer of salt. No parts may be uncovered!. Salt should be rubbed in eventual folds of the legs. The next hide should be spread flat on top of the previous hide, hair down, flesh up. The flesh should be carefully covered with a layer of salt, etc. The stacks that are thus formed should not be too high., half the length of a normal person. Stacks must be turned after a couple of days. The lower hides must come on top and the top hides should go below. This is important to avoid hides from "heating" in the centre of the pack. One should not forget that the bacteriological process is continuously at work and hides in the middle of the stack would tend to heat due to the bacterial action and cause heavy putrefaction defects if their position is not changed.

    In the first 20 days after slaughter and salting, the hide will lose some 20/22% of their weight. This is a sign that hides are properly curing. Salt is partly diluted by the hides' own water content which is drawn out by the hygroscopic characteristics of salt and the thus formed salt solution penetrates the fibres resulting in proper conservation. A wetsalted hide when it is properly cured will contain less than 50% humidity and the salt saturation level of these 50% should be around 85%. In countries with high labour costs salting is done in drums, which needs to be kept under strict control as the temperature of the hides must be kept below 25°C to avoid heating and thus putrefaction. Drumming hides generates heat due to friction.


    Brine curing is an industrial development of hand salting. Hides are dipped in a saturated salt/water solution. The hides and the water should be kept in motion with paddles in order to obtain good penetration of the salt in the fibres of the hides. This method is dubbed the raceway curing. The salt vat is an oval with an oval island in its centre. Two rotating paddles keep the brine solution and the hides in motion.

    With this method you can cure hides within a period of about 24 hours. After the 24 hour curing the hides should taken out of the raceway and hung for draining. Proper draining is done in 15 days, but can be accelerated by pulling the hides through a wringer.
    Brine cured hides don't look too good. They are usually dirty, but when you scrape off the dirt you generally find under the dirt a beautifully white cured hide. This method is of course for a more industrial approach and should be considered for operations that have a daily production of some 200/+ hides.
    The salt content in the brine must be kept at saturation level.


    A combination of wet salting and drying is dry salting. Hides that are wet salted can be dried afterwards and be turned into a dry salted hide. Dry salted hides have a better quality than air dried hides, whereas wet salted hides are of better quality than dry salted hides. Dry salted hides are found in countries with a hot climate where wet salted hides would not maintain their natural moisture. What happens in hot climates is that wetsalted hides slowly dry out at the edges when undergoing curing or while awaiting shipment. The inner part of a hide would contain a high percentage of moisture whereas the outer edges would be bone dry. Due to the temperature of the environment it is likely that the humid core of a pallet of wetsalted hides will slowly deteriorate. Once a hide is dry contact with humidity should be avoided, unless for rehydration for processing, as it will re-start bacterial growths and putrefy, whereas if the hide is completely dried, there will be no bacterial growth.


    Storing of preserved hides is of great importance. All hides and skins, whatever their method of conservation must be stored in the shade in an as cool as possible environment with adequate ventilation. The hides and skins should not touch the warehouse floor, hence they should be kept on pallets. Dried hides and skins should be shielded against humidity in general and liquids in particular. Water dripping on a dried hide or skin will cause putrefaction, that will manifest itself after re-hydration for tanning as a hole.

    Dry hides and skins must be treated against insects and parasites with insecticide and during storage it is imperative to check the effectiveness of the insecticide. A clean warehouse floor is not recommended. Some thin dusting of the warehouse floor with insecticide will bar insects and parasites from entering the warehouse or kill them after they do gain access.
    Wetsalted hides should maintain their natural moisture and should not be allowed to dry. Since the loss of moisture is a physical process that cannot be stopped unless in a controlled environment it is recommended that wetsalted material is shipped between 21 and 30 days after slaughter. Wetsalted hides are mainly sold on a weight basis, hence excessive loss of moisture, after 30/35 days, would unnecessarily damage the seller economically. The ruling international hide and skin contracts contains a moisture-loss table.

    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 10:09:47 AM

    Hides are seldom processed  after flaying, but are held in a state of preservation and tanned later. Hides and skins begin to putrefy immediately after removal from the animals body. After slaughter the immune system ceases to function. Bacteria on the hide surface invade the epidermis and dermis along the hair papillae.
    Putrefaction is caused by digestive action of micro-organism on the hide. They secrete enzymes that attack the proteins of leather. There are chemicals that can remove or kill the bacteria. Precisely, the chemicals that kill the bacteria are called bactericides whilst those ones that stop or inhibit their active life are known as bacteriostats. In some cases the already deposited enzyme on the hide could continue to attack the hides whilst the bacteria is dead or inactive.
    Putrefaction only happens when in the hides is present water. Commonly, salts, acids, or alkalis, bactericides in high quantities are used to prevent putrefaction. The water contained into the hide dissolve tese chemicals, that penetrate in all the section of the hide and putrefaction is inhibited.
    Obviousily, the removal of water by drying is a further method of preservation.
    The hides are generally stored as they are received by the tannery on pallets in ventilated or air conditioned and/or cooled areas, depending on the metod of curing choosen. 

    The curing  for long- time preservation (6 months) is based on the following methods: salting, brining, drying, salt drying and pickling. The methods for short-time preservation (2-5 days) are cooling, using crushed ice or refrigerated storage and biocides. The selection of preservation methods largely depends on the market structure (consistent supply from abattoir, hide and skin market) and geographical distribution of raw material. 60 - 70% of hides worked by tanneries in Austria and Germany and 30% in UK is cured with short time preservation methods.

    Short time preservation

    One of the short-term preservation methods is cooling. If the time between flaying and processing in the tannery is no more then 5 - 8 days, it is possible to cool the hides/skins, after draining the blood, to a temperature of 2°C. Crushed ice, ice-water or cooled storage may be used for this purpose. The cooling chain must not be interrupted during transport and storage. Obviously, with this technique - processing fresh hides - the use of salt is avoided. It is environmentally friendly for short storage periods. Under normal circumstances no salt is discharged in the waste water from the soaking. The quality of the hides is good; they are softer and have more regular neck parts, so easier to process, the yeld is higher (1-1,5%) respect to the salt cure system. The discharge of electrolyte into the environment might have a significant effect on both aquatic and plant life, with most fresh water species unable to tolerate even relatively low concentrations of electrolyte in the water. Discharge of electrolyte is even more of a problem in areas where fresh water is scarce, and contamination of the watercourse by salt can have a highly adverse effect. Also, where waste water is used to irrigate land, the impact of the salt content on the land has to be assessed.

    There are, however, several restrictions when using short-term preservation methods. Ideally the slaughterhouse must be relatively close to the tannery (not overseas). The raw material must be processed almost immediately (depending on the chilling method, between one day and ten days).  Raw stock cannot be bought in great quantity when prices are lower . The transport costs can be greater due to either extra weight (ice) or the cost of refrigerated units. The energy consumption can become prohibitive if the hides are stored for more than one week. The system of collecting/trading hides in any individual country or region may not suit the use of short-term preservation methods; for example, if a substantial proportion of hides are imported or exported, the system may not be practical/economically viable. All the above points can be against short-term preservation as it can increase the cost of the raw material. In practice, chilling can be adopted in all countries, but in some countries it is less cost effective than in others.

    Wet salting

    Wet salting is the most common method of preserving hides in Europe, North America and other temperate climates. The cold flayed hide is spread out, flesh side up, on a concrete floor and well sprinkled with salt (sodium chloride). A second hide is placed on the first one and also sprinkled with salt. This is repeated until piles 1,5-2,0 m are formed. The top hide is well covered with salt. The pile is left for days, so that the salt dissolves in the moisture in the hide and the brine permeates the pile. The quantity of salt employed amounts to 25-30% of the hide weight. During this period of time, the hides lose some moisture and consequently the weight decreases about 10% of the drained weight. The use of improper sized salt or dirty used salt causes stains and defects that reduce the leather value. Where bad situations exist during salting, in pack and during storage, skin and hide defects due to germ life, heath, lack of salt, become accentuated and the longer such stock remains in storage, the more extensive the defects become.

    It is better to use clean mineral salt. In marine salt or in re-used salt can be present halophilic bacteria, that originate red or coloured stains named "Read heat". Their evidence denotes that some putrefaction has happened with the consequent weakening or damage of the skin. The particle size of salt is important. The salt made on particles too fine gives pasty patches and the covering is uneven. In the opposite case, it readly falls off the skis in handling.  Very large crystals of salt or large irregular matter, cause depressions or pits in the grain. The conventional salt cure system has the advantage to penetrate deeply in the hide ;  the dehydration effect makes easier the water penetrazion during soaking inside the hide. Salt provokates also the coagulazion of globulins, simple protein, that in its presence are dissolved easily in water during soaking.

    The disadvantage of this method is due to the huge amount of chloride in the waste-water. The most common factors that  must be considered when are found curing defects in the hides are temperature of storage, time of storage, humidity, hair length, the particle size and the quantity of salt employed.  If the temperature of storage is too warm, there is an increase in the rate of deterioration even with good salting. An insufficient time period in a salt pack or brine will give undercured  hides. Leaving stock for long periods in storage, often, results in stains or discolorations. A high humidity, which allows for moisture to be absorbed by the stock, may encourage staling and spoilage. A very low humidity can bring about an uneven drying out of the stock. Dry areas, often, are not fully hydrated during soak. In this case  "hard spots" can be found in leather.  An uniform air circulation in storage space is desiserable. Excess direct draft may dehydrate stock in spots. Long-haired stock carries more dirt or filth which works against the best cure. 

    Brine curing

    This method is applied in North America. The advantage of brine curing is represented by the less time of process; therefore, less capital is tied up in hide inventory. The hides are cleaned by washing with water and then soaked in pits or a raceway system in a very strong salt solution (brine). The brine contains about 15 kg salt to every 45 liters of cold water (30° Bé) . The time of this treatment depends on the thickness of hide. The uniform salt penetration requires about 15 hours for heavy hides. Then, the hides are drained and piled. Generally, after this operation, the hides are sprinkled with salt. The exhausted brine liquor may contain halophilic bacteria. For this reason, the purity and the strength of brine liquor must be checked before its re-use.

    Dry-salting curing

    The hides are salted by the conventional system or brining curing. Then, they are hung up to dry. After drying, the weight decreases, consequently the cost of transport is lower than the wet salting system. It needs to point out the following aspects:

    a) Drying must be carried out gradually and evenly to avoid local or extended gelatinizations. In this case the hides show a horny feel. When soaking is carried out, these zones dissolve away leaving holes in the hides.
    b) The soaking operation of dry salted hides requires a longer time than wet-salted hides those one.


    In this method, overall when heavy hides are dried, it needs to consider the following aspects:

    a) Drying too slow : putrefaction may verify before the moisture content is low enough to stop bacterial activity.
    b) Drying too fast:  the temperature too high provokates local or extended gelatinizations. The hides show the defects above mentioned.

    Drying can be executed by different ways: ground drying, sun-drying, frame drying.  The ground drying provides that the hides are spread out on the ground . The frame drying, that consists in straining out the hides on frames, sheltered from the direct rays of the sun, is the best system. This gives less danger of heat damage and a regular, flat shape of hide.

    Pickling of hides and skins

    Soaking, unhairing, liming, fleshing deliming, bating and pickling operations are carried out in the origin country of the raw material. This method of curing is practised especially for sheep skins coming from Middle East, UK, New Zealand and South Africa. Thus, the tanner is relieved of costly and heavy effluent problems linked to beamhouse operations. The long term preservation is secured only when the same degree of acidity and salinity reachs all the section of the skin and its pH value is around 1,5. Small amount of fungicide or anti-moulds may be added to the pickle liquor to prevent mould growths.
    After draining, the skins packed in waterproof crates, can be stored for several months if they are kept  cool. At  temperature of storage higher than 30°C, the acidity may cause damage to the skins.  Before tanning operation, the skins are depickled in order to neutralise partially the strong acidity of the skin structure.

    Tanning processes

    Adequate hide preservation can be obtained by carrying out light tanning processes.  A very light vegetable tannage gives to the hides excellent preservation. After the tannage is possible to dry the hides and the sorting is made easier. A light tannage confers to the skin the minimum characteristics of this determinated tannage. Consequently, the subsequent tannage can give to leather  its own properties.

    Use of biocides in curing
    In general there are no biocides used in the preservation of raw bovine hides in Europe. Biocides that were used in the past include PCPs, DDT, benzene hexachloride, HCH, dieldrin, arsenic and mercury based ones. The use of these biocides is prohibited in Europe. Nevertheless, skins imported from South America, the Far East, Africa or India, could still be treated with biocides already banned in the EC. Furthermore, hides and skins could contain traces of biocides because of animal treatment with these substances prior to slaughtering.

    HS.P.1.5 - Grading

    Grading to accepted standards
    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:10:29 AM

    Although in several countries hides and skins are sold on a tannery run (TR) basis, or tel quel, meaning that the lots are mixed independently of the quality of individual hides and skins, it is recommended to sell hides and skins on a selected basis. Normally selling on a selected basis favours the shipper with a better price in the international market, and buyers are generally happy to pay more for a selected hide, which gives them some sort of a guarantee that the supplied material is suitable for the purpose they bought it.
    There is a general basis of a global selection standard. It is based on natural defects, manmade defects, size, shape and weight. The application of this general standard with the quantification of the defects per grade depends on each individual country. Climatical and environmental conditions play an important role. The better these conditions are the lower is the number of defects per grade.
    For instance, if in a country there are no thorny bushes, no barbed wire, then these defects do not count in qualifying a hide in a selection grade, whereas in areas with thorny bushes and/ or barbed wire, the damage caused by these circumstances becomes relevant and is considered in the selection criteria. The same is valid for brand marks. In Europe where brand marks are absent, they are not part of the selection criteria for European hides, whereas in the USA where branding of cattle is still frequent, the number of the marks and their size are part of the selection criteria. Hence each country or production area has its own selections standard and reputed exporters or traders refine that standard with personal details in order to differentiate themselves from the competition. Regional presence or absence of certain qualifying or disqualifying factors determine the suitability of raw materials for the finished product. Regular buyers from specific areas know what shipper has what standard quality and award him with a price that reflects his selection standard.
    Price is related to overall quality and grading. The better the selection, the better the price that can be demanded on the international market. It is fundamentally wrong to adjust the quality according to the price.


    Natural defects is anything that is not caused by men. It can be monsoon damage manifesting itself in putrefaction holes on the bellies of small animals in Asia, or scars made by horns, barbed wire, thorns, insect bites, parasites, illnesses, manure, etc. Some natural defects can be avoid. Substituting barbed wire with electrical fences, vaccinating animals against parasites are remedies which give positive results. Keeping cattle clean from manure improves the hide quality.


    Man-made defects are totally unnecessary and with good organisation can be avoided and eliminated. Branding cattle, maltreatment damage the animal's hide (haematomas and worse)  can be avoided when it is still alive, butcher cuts and holes, bad shaping can all be avoided at the abattoir level. Putrefaction defects can be avoided at the conservation and transportation level. All these defects if present singularly or accumulatively downgrade a hide or skin and thus its commercial value. Proper preparation of hides for shipment is in the eye of the buyer part of the manmade defects. If a lot presents itself well and professionally prepared automatically it influences the state of mind of the buyer upon arrival of a certain lot.


    The grading of hides and skins is not limited only to defects, but it is extended also to the separation of weights. Some markets sell from calf to bull in the same parcel, but obtain because of this a limited price for their material. The tannage of small skins is different from that of large skins. The treatment is different, the chemical processing is different and the value of the hide or skin itself is different. For that reason there is an unwritten global standard that specifies a weight separation. The ranges for cattle hides are more or less -/2.5 kgs, 2.5/5 kgs, 5/8 kgs, 8/12 kgs, 12/16 kgs, 16/22 kgs, 22/28 kgs, 28/35 kgs, 35/+ give or take a kilo here and there. Goat and sheepskins are less defined and are usually separated in small, medium and large where the range is wide like in the USA, northern Africa or Pakistan, whereas in Sub Saharan Africa the width of the range is small and skins are sold as they come. Dry skins are separated by weight.


    There is no such thing as a clearly defined international standard. An international standard or norm is virtually impossible, because each region of origin has its own characteristics in terms of natural and manmade defects, and in terms of the characteristics of the hide or skin themselves. Therefore you can expect a certain standard only within a well defined area. Suppliers within a defined area can determine their own standard as well, but that personalised standard more or less reflects the regions standard, and is usually a refinement.  The US National Hide Association published in 1979 a booklet "Hides and Skins" prepared by their Education Committee. This booklet is an excellent guide laying down the general basic rules for the production and preparation of cattle hides and calfskins in the United States. This guide can form the basis for all wetsalted hides and skins all over the world if properly used with common sense and adapted to regional requirements.
    There is a general consensus on one basic rule: any defect presenting itself on a bovine hide within 10 cm from the outer edge of the hide is not considered a defect. Any defect further than 10 cm from the outer edge counts in full as a flaw.


    Unido have developed in collaboration with FAO a couple of years ago a very useful guideline for the selection of East African hides and skins. This came under the Africa Regional Leather Programme US/RAF88/100 and US/RAF/98/200. It deals mainly with dry hides and skins which are becoming less common, but nevertheless the guidelines if used as such and with consideration and adapted to each region, are an excellent selection basis for African origins.
    The following link leads you to these selection standards: Unido H&S_Standards.pdf 


    There are several international agencies who provide a quality certification service. This sounds better than it actually is. Having hides and skins certified by these agencies doesn't mean by any means that the contracted quality is met by the exporters and guaranteed by the certification agency. In fact the agency takes no responsibility whatsoever neither for the quality, nor for the quantity shipped. Sometimes this quality certification cannot be avoided as some countries require this service when equipment or commodities are imported into their country.
    Some countries require certificates that state the absence of certain chemicals. This certification is ruled by bilateral agreements of the countries involved. Such certificates can be obtained by the exporters from their local authorities or downloaded from Internet websites.
    Wet salted hides are sold on a per kilo basis, hence the net weight is of vital importance. The weighing provisions and certification requirements can be found in the ruling international contracts.


    A reliable exporter exercises quality control over the by him produced goods. This is part of the quality standard a particular producer assumes. There is no other credible control.
    In some areas buyers can find a system of buying agents, where local hides, skins, and leather experts offer their services to coordinate quality control and export management for a commission percentage. Some work, others don't. However none of these buying agents take a personal responsability. When a lot goes wrong, it becomes a matter between buyers and sellers. The service works for proper communications and documentation.


    Each country, or group of countries like the EU have their own veterinary regulations, that deal with the import of raw hides and skins. These regulations are part of a bilateral agriculture agreement between exporting and importing countries. It is the seller's obligation to provide the buyer with the correct certification that is required by the importing country. Veterinary or health certificates are available with the local veterinary authorities or can be downloaded from the Internet. Some countries do not require particular forms and accept any form as long as it properly states the required data.
    The EU demands its own certificate to be used, called the "Official Declaration". It is to be noted that contrary to the general belief that the Official Declaration can be presented in any of the official EU languages, you have to present the document in the language of the country in which the goods first land, as that is the point of entry into the Union. Even if the final destination of a container of hides is for example Germany, if it lands in Italy, the official declaration must contain the Italian language! In this case to avoid unnecessary bureaucratic hassle, one best presents the certificate in German, Italian and English.

    Modified by:LANCEY, Ms. Raphaelle 24/05/2007 10:10:29 AM

    HS.P.1.6 - Packing

    Salted and dried hides and skins
    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:11:28 AM

    There is no standard export packing. Packing is both a practical matter as a matter of proper conservation when you deal in raw materials. Palletized packing is a requirement that originates from common sense. It facilitates loading and unloading of a container or truck.

    Dry hides and skins are to be carefully treated with insecticides before packing and loading. Fumigation of a container before departure from the premises of an exporter adds to the safeguarding of the quality of the loaded hides and skins. Dry raw hides and skins have an inconvenient weight versus volume ratio, which makes transport of this material rather expensive. Just bundling dry material gives a load factor of about 5-6'000 kilo's per 20' container, whereas if the material can be pressed in bales, one can increase the load factor up to 100% and fit 9-10'000 kgs in a container for hides and up to 8-9'000 kilos for a container of skins.

    Pressing of dry hides and skins is a delicate matter. Pressing too little does not improve the load factor to the required percentage, whereas pressing too much cracks the hides over the folding lines and causes thus unnecessary damage.

    Pressed bundles are held together with iron bands. To safeguard the packed hides it is necessary to pack the hides with the flesh out. Bales of skins are best wrapped in cloth before they are encircled with the iron bands. The shipper must ascertain that the container on which his hides and skins are to be loaded is free of holes to avoid that rain or sea water can find its way to the loaded dry material.

    Choice of packaging
    Contributed by: PACKit - Export Product Module, International Trade Centre
    Last updated: 08/02/2007 3:55:36 PM

    The following text has been extracted from the "Export Product Module Packit", a technical paper developped by the International Trade Centre based in Geneva. For more information please go to:

    Among the requirements emphasised by the European tanning industry and importers of raw hides, skins and semi-processed and finished leathers, are the need for raw product imports to be of high and homogeneous quality, with regular grading, and for goods to be delivered within the terms of contract.
    Actual practices in developing countries reveal two things: that the transport of hides and skins does not always occur under the best of conditions; and that there is a lack of information in the leather sector on packaging materials and systems.
    The choice of packaging material and packaging type is usually dictated by the nature of the product and the mode of transport required for export.
    For raw or semi-processed products, the change in the length of the trip from seller to buyer may even change the weight of the goods. The expected loss of weight is usually accounted for per day of delay in shipment by a formula. This is usually applied as part of contracting, and varies for raw hides and skins depending on whether they are dry, dry salted or wet salted.
    If wet salted hides and skins are tared, no less than 10% are check weighed; they are then buffed once on each side on a clean surface, and reweighed. No sweeping of the hides and skins is allowed other than to remove encrusted salt.
    On dry and dry salted hides and skins, tare is to be allowed for packing and any other extraneous matter. As previously mentioned, shipments can be examined on arrival at their destination. There are usually agreements between seller and buyer as to sampling techniques. It is usual in the case of wet-blue hides and skins, for example, that samples for analysis are taken from a minimum of one package out of every five. An independent analysis may need to be carried out in accordance with the official methods of analysis of the International Union of Leather Technologists and Chemists Societies.
    The availability of suitable packaging materials in a country of origin will always be another factor, although packaging materials are commonly imported to many developing countries if necessary, especially if for re-export.
    Diseases and infections can have a major impact on hides and skins*. In some areas, parasite damage is a serious problem. Sources of infestations can be difficult to identify, but large movements of human and animal populations can spread disease and parasites. Climatic conditions in many developing countries favour rapid decomposition, and thus make preservation difficult.
    Inadequate storage conditions and lack of preserving agents may lead to damage of grain and texture through decay in particular areas of the leather.
    To avoid some degree of deterioration during storage, as well as more substantial damage attributable to infestation by insects, for example, the period of storage should be kept to a minimum. For similar reasons, transportation procedures should be as rapid and direct as possible. Prompt storage and transportation of hides and skins will also minimise the amount of capital expenses deployed in the maintenance of large stocks of raw materials.
    Appropriate storage and transportation procedures vary according to the method of preservation that has been used.

    * Committee On Commodity Problems; Intergovernmental Group On Meat; Sub-Group On Hides And Skins.Trade Restrictions on Hides and Skins. Seventh Session, Rome, 4 - 6 June 2001. (CCP: ME/HS 01/4).


    To prevent handling damage during transportation from the slaughterhouse, or from the place of private slaughtering, to the place of preliminary treatment, proceeding tanning is crucial for the ultimate production of a quality hide or skin.
    It is recommended that hides and skins should be transported in leak-proof plastic bins or containers, which must be well-scoured and perfectly clean. These containers must have covers of the same material, or of plain woven fabric.
    The cleanliness of the containers and lids is essential in order to delay the onset of decay for as long as possible. Transportation of hides and skins from places of slaughter should take place as immediately as possible. It is recommended that the containered hides/skins are transported in a refrigerated environment.
    In other methods of transportation, the small batch containers are replaced by fairly largecontainers. Trolleys are fitted with leak-proof, ventilated, lidded recipient containers.

    Below: Schematic diagram of a fresh hides/skins transport bucket and trolley


    Raw hides and skins are usually packaged in bulk. They are sorted first according to size.
    Air-suspension dried material is compressed into rectangular form using a screw press or a hydraulic press, after arranging the skins or folded hides in layers.

    Below: Suspension dried cattle hides under the press.

    Source: Arcapelli Sas

    The packaged air-suspension dried material is shown in the figure above. The bale-packaged air suspension dried hides and skins are shown below.

    Suspension dried hides after pressing:

    Source: Arcapelli Sas

    Air-suspension dried raw hides and skins are usually transported in sealed freight containers after applying insecticides to the materials. This is because they are prone to attack from bacteria and moths unless properly treated. Once on a pallet, the stacked, pressed load can be wrapped with woven or non-woven polypropylene film. Some producers use shrink plastic wrapping. The general idea is to provide a waterproof covering. Pallets are then placed in a 20ft container holding up to 20 pallets of 80x120cm - i.e. up to 40.000 hides. 

    Below: Bale-packaged air-suspension dried hides and skins.

    Wet-salted hides are folded into bundles with the flesh side out, and are then tied with a string. They are folded along the mid line (back bone), turning in the shanks.
    It is to be noticed that, at this stage, pallets play an important part. If they are made from wood, it is recommended that the wood be treated. Direct contact between the hides/skins and the wood of the pallet is avoided by covering the pallet with a sheet of plastic film before stacking the hides/skins on it. The stacks are best when between 1 and 1.5m high, and are usually covered with a plain cloth of natural fibre (usually cotton or jute) to prevent insects from reaching the stacked hides/skins.
    Cold storage is also recommended, at temperatures up to a maximum of 10°C at a relative humidity of 70%.


    Pickled skins require extra care and must have a low pH. They need to be handled with rubber gloves to avoid acid burns. Skins are normally folded into a sausage roll and then packed in polythene bags in packs of 12 pieces (see figure in previous section).

    Below: Pickled skins in polythene sacks.

    The PE bags/sacks help keep the pickled skin wet and with a low pH. The plastic in common use is clear 150-micron PE. The dimensions of the sack are approximately 900x100mm. The average weight contained is approximately 30-40kg per package, constituting on average 80 dozen pieces. The sacks are sealed by sewing.

    Plastic sacks:
    Sacks made of plastic film are usually single-wall sacks. The most common plastic used is polyethylene. The various qualities used include LDPE, LLDPE, HDPE and PE or PP tape for woven sacks. The dimensions of woven sacks are always given as width (W) x length (L) in millimetres.


    These hides and skins are packed on pallets and wrapped with polyethylene sheets to retain moisture during storage.

    The figure below shows air dried goatskins pressed in bales ready for shipment.

    Source: Arcapelli Sas

    Below we have Wet-blue hides and skins packed on wooden pallets, before and after strapping.

    The figure below shows Wetblue skins wrapped and palletized under loading.

    The wet-blue hides are folded and stacked on a pallet. The number of hides on the pallet varies depending on the size of the hides. The wrapping is a cloth material.


    That is an example of Crust leather (rolled).

    After rolling, crust leather is shipped in bundles. The bundles are usually packed in a PE sack, but this depends on the wishes of the customer. There are no set standards.


    The following are practical examples of semi-processed leathers packaged for export on wooden pallets inside freight containers. All methods are applied in one or another of the 35 exporting countries. It is to be noted that sometimes non-standard pallet sizes are used where the standard SI 200 size should be used instead.

    Goatskins/sheepskins: Wet-Blue Chrome

    • No. of Pallets: 20
    • Size of Pallet:1.1 x 1.1m
    • No. of Pieces: 5.500 - 6.500 of assorted sizes

    Hides:Wet-Blue Chrome

    • No. of Pallets: 12
    • Size of Pallet:2 x 0.9m
    • Average No. of Pieces:1500 pieces in a container
    • Average Size per Piece:24 sq. ft.

    Hides: Crust

    • Thickness of Material:1.8mm - 2mm
    • No. of Pallets: 16
    • Size of Pallet:1.4 x 0.9m
    • Footage per Pallet:5000 sq. ft.
    • Thickness of Material:1.6mm - 1.8mm
    • No. of Pallets: 16
    • Size of Pallet:1.4 x 0.9m
    • Footage per Pallet:5000 sq. ft.
    • Thickness of Material:1.4mm - 1.6mm
    • No. of Pallets: 20
    • Size of Pallet:1.25 x 0.9m
    • Footage per Pallet:5000 sq. ft.


    Upholstery leather is not regarded as leather in its pre-processed state. It is destined specifically for use by upholsters. It is considered a class product, and it needs special protection. These leathers are packed first in PE bags, and then in strong corrugated boxes or wooden cases made of treated wood to protect against insects and other pests.

    Packaging materials
    Contributed by: PACKit - Export Product Module, International Trade Centre
    Last updated: 08/08/2006 7:29:31 PM

    Materials used for packaging hides and skins are made from:

    • Wood, in the case of wooden pallets
    • Hessian cloth, jute cloth, or cloth made from cotton
    • Polyethylene or polypropylene film


    The following terms and types of terms are used in relation to plastic material properties:

    • Thickness of plastic films, commonly given in microns.
    • "Tensile strength": this expresses the tensile force required to rupture a given area of material. Tensile strength is usually expressed either in force per unit cross-sectional area, or in force per unit width.
    • "Permanence": this can be described as the general ability of the product to withstand changes in environment without the loss of essential properties.
    • "Moisture resistance": some products need protection from outside air moisture, and others require that the moisture contained should not be allowed to evaporate through the package. Resistance is given normally as the amount of water vapour that transmits through the material under certain test conditions. It is called the water vapour transmission rate or moisture vapour transmission rate, and is expressed in g/m2/24 hours.

    Polypropylene (PP) is often coextruded with PE. Coextrusion is a method of combining two or more plastic materials by extruding them through one common nozzle. The different layers stick to each other, giving improved properties.
    As wrapping films are usually sold by weight, the comparison of yield and thickness becomes essential.
    High Density Polyethylene (HDPE) has better barrier properties then LDPE and is also more rigid. It withstands temperatures of 120° C.
    Low Density Polyethylene (LDPE), the most widely-used plastic, is non-toxic, has good barrier properties against moisture, and has reasonable grease resistance. LDPE has good heat-sealing properties and will retain its flexibility at very low temperatures. The disadvantages of LDPE are its fairly high oxygen permeability, its limited aroma barrier, and its rather low rigidity.


    Hessian is the plain weave variety of jute. Other varieties are the double-warp tarpaulin, a cloth with double warp yarn but single weft, plain-woven, and of fine construction; and twill, which is usually a double-warp fabric with a diagonal line in the weave so that the cloth cannot unravel. Jute may be treated to become waterproof, rot-resistant or fire-resistant.


    Hides and skins packaged on pallets are secured with metal or plastic straps while the hessian sacks are stitched (figure 16).

    Below you can see products packed in hessian sacks


    Markings for packaging identification and handling are usually in line with details contained in shipping documents. Packages for raw hides and skins bear the following details:

    a) Product/type, e.g. "sheepskin", "goatskin"
    b) Origin, e.g. "India"
    c) Weight category
    d) Selection, e.g. quality grade
    e) Batch number
    f) Number of pieces

    For wet-blue hides, information on area in square feet and on substance/thickness is added.

    Marking requirements are usually mentioned in official contract forms. The most important are the following:

    • Goods sold to be shipped: to be sorted into different grades, to be packed and marked separately and each package to be clearly marked.
    • Goods sold by area: the area to be marked on each item so as to be legible at destination.
    • If goods of one size are to be bundled together, the size is to be stated on the bundle.
    • If goods of different categories arrive insufficiently marked, re-opening charges thereby incurred are to be for the seller's account.
    • The "English" text should be the definitive text unless otherwise agreed with the buyer


    • All raw hides and skins are prone to attacks by pests, and therefore all packages should be stored in warehouses and containers where they are safe from such attacks.
    • Air-suspension dried raw hides and skins can easily crack if subjected to excessive force from the press machine during packaging. The material should also be kept away from moisture to avoid spoilage.
    • Wet-salted hides are folded in such a manner that the flesh side is exposed to the air, and should therefore be kept away from liquid contaminants.
    • Pickled skins must be packaged in materials that withstand low pH, and should be kept away from heat as they gelatinise at relatively low temperatures. Containers packed with pickled skins should bear clear markings showing that the goods should be kept away from heat.
    • Wet-blue leathers are packaged and tightly sealed with polyethylene materials to prevent loss of moisture. Loss of moisture leads to deterioration in quality, as when the material becomes dry it must be re-wet before further processing.


    Importers have often indicated that uniformity and reproducibility of raw products are essential requisites. Irrespective of the stage of processing, goods delivered should correspond to what was ordered - i.e. shipments should contain goods of uniform grade, finish, colour and thickness, made with the same manufacturing process and identically packaged.
    At the raw stage, hides and skins should be graded and trimmed according to the importer's specifications. Uniformity is also essential in such aspects of finish as colour and grain. Delivered goods should be identical to the samples on the basis of which the transaction was concluded, and should have identical properties piece by piece.
    Proven uniformity saves considerable time for the importing tannery by avoiding lengthy checks and measurements of lots received. Uniformity in weight can be obtained by making batches of the same weight-range and trimming them according to generally accepted standards. Uniformity in size is achieved by machine measuring. Uniformity in thickness can be achieved by splitting leathers in layers as requested by the buyer, or by sorting pieces into lots of the same thickness to meet the usual requirements of the market. All these practices have an impact on packaging.
    Reproducibility in process is important for those developing countries which export semi-finished and finished leathers. This requires quality control in the factory so that successive partial shipments correspond to the terms of the sales contract. Reproducibility in processing is achieved by using the same procedures, chemicals, dyes and resins, so that exactly the same shades and finish are achieved.
    Reproducibility of the mechanical and physical properties of the leather may be ensured by regular laboratory testing of the batches as regards breaking point, stability under conditions of heat, cold resistance to water, etc.*
    It is necessary that the exporter fully understands the packaging requirements of the importer. Exporters should have up-to-date knowledge of the availability of packaging materials in their particular country . The cost implications of packaging materials and styles should be considered without prejudicing quality requirements.
    Essentially, packaging should help to prevent deterioration in quality of raw hides and skins and semi-processed leathers. The quality at destination and through the distribution chain should be the same as at the time of packaging. 
    The exporter must provide information on each package/pallet on his product specifications, indicating the composition, quality grading and quantity. These also allow the tanning industry to differentiate between the wide range of grades and sizes of raw hides and skins and semi-processed materials originating from various animal and/or country sources.
    Convenience in package handling is important. It is therefore recommended that packages are limited to weights which are easily manipulated by hand or forklift, which are easily loaded, and which enable maximum loading capacity to be exploited either in a vehicle or in a container.
    Delivery on time is a requirement that more than any other applies to all processing stages. Exporters face a number of difficulties, including distance, irregular means of transport, and such production problems as power cuts, etc. Adherence to a time schedule based on the time required to produce, procure packaging material, pack, transport to post or airport, clear customs, and load, helps to avoid untimely deliveries, which can result in cancelled and unrepeated orders. In such situations buyers look for other suppliers until confidence is reestablished.
    It is recommended that prospective exporters of hides and skins contact the traders, agents and tanners in target markets, giving details of their company, materials offered, selection of grades, quantities deliverable per month, available packaging materials and styles, the exact quantities of each grade and their prices. Offers should be clear and concise. As far as semitanned leather is concerned, the same procedures should be followed. Effective communication between buyers and sellers is vital if good business relations are to be developed.
    Developing countries have difficulty obtaining the information needed effectively to export their commodities, and buyers in developed countries increasingly need to find new sources of supply. Participating in trade missions and trade fairs and the publication of trade information are ways in which contacts can be established and information exchanged between buyers and sellers. The increasing availability of internet technology is further overcoming the barriers to such exchanges. However, in this fragmented and diverse industry, the limited availability of trade information remains a constraint to the effective development of exports, particularly from African countries.
    With increasing awareness of environmental issues, the leather processing industry must address the concerns of environmentalists and consumers. The transfer of technology and training to developing country producers in production/packaging is beneficial.
    It is useful to each country's group of exporters of hides and skins to discuss amongst themselves such issues as wastage of hides and skins, non collection and damage, statistical intelligence, restrictive trade policies, environmental constraints and commercial trade information.

    * Committee On Commodity Problems: Report of the Seventh Session of the Sub-Group on Hides and Skins. Rome 4-5 June 2001. (CCP:GR-RI-ME-OF 01/6-Rev1)

    HS.P.1.7 - Protecting endangered species

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:13:33 AM


    During the second half of the 20th century the hide and skin trade and the leather industry have become very environment conscious and forerunners in the field of protection of endangered species and the ethical treatment of animals. A lot has been done. A lot can still be done.
    The so-called endangered species are not indiscriminately targeted anymore by the trade and industry. Poachers remain, but have rarely or no outlets in the regular trade or industry. When in the past reptile skins originated from indiscriminately hunted animals, now they are supplied by reptile farms. Kangaroos and deer are still hunted but local governments issue licenses for the number of animals each hunter is allowed to kill per season. This number is based on scientific research by competent authorities, which aims on culling the weak and old animals, making thus place for the younger to proliferate, keeping livestock at steady levels.
    In 1973 the Washington Convention (CITES) established precise guidelines for the trade and industry with the purpose to save certain species from extinction. CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) is an international agreement between Governments. Its aim is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. CITES works by subjecting international trade in specimens of selected species to certain controls. All import, export, re-export and introduction from the sea of species covered by the Convention has to be authorized through a licensing system. Roughly 5,000 species of animals (and 28,000 species of plants) are protected by CITES against over-exploitation through international trade. In a large number of developed countries it is a criminal offence to possess hides or skins or leather products made from protected hides and skins, unless accompanied by or traceable to a CITES certificate. For more information go to www.cites.org


    HS.T.1.1. - History of Hides and Skins marketing

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:43:34 AM

    Hides and skins have always been produced from pre-historic times to our day, and mankind will continue to produce hides and skins also for all times to come. It has always been considered a pity not to utilise a hide or skin. In ancient times the requirement for the consumption of food in general and meat in particular was such that even in a small community a large number of hides and skins became available, exceeding the necessity of that community for clothing, footwear and protection from the elements. That generated the requirement to find buyers for hides and skins. A pyramidal system developed itself for the collection of hides and skins wherever they were produced. This way a value chain developed.


    There are generally two types of producers in the value chain of hides and skins. We have the small country butchers who produce a relatively limited number of hides per week and you have abattoirs which produce relatively larger quantities of hides and skins.

    The relativity depends on the size of community in which the butchers or the abattoirs work, and whether they produce also quantities of meat which are not designated for local consumption. It is obvious that abattoirs in large metropolis produce more hides and skins than abattoirs in provincial cities.

    In the pyramidal collection system small collectors buy a couple of hides and skins here and there from home slaughter, small butchers or small abattoirs. That can be to the tune of even a piece at a time. These small local collectors who store some 10/50 hides and some 100/500 skins at a time on their turn sell their collected quantities of hides and skins to regional collectors who typically trade quantities of 100/500 hides and 1000/5000 skins. At the end of this pyramid is the big time collector who can act also as exporter, or in some cases can be a local tannery. Due to the lack of financing through official channels like government and banks, the collection system is formed particularly in developing countries by the availability of funds with the individual collectors. Very small collectors generally work hand to mouth. They buy a couple of hides and skins with the funds they have at their disposal, then sell them and with the available money the whole circle starts again.

    Larger collectors either work with their own funds or get a prepayment from the exporter or tannery who are at the top of the pyramid. With the prepayment they buy hides and skins from their suppliers and reimburse the prepayment with the delivery of the hides and skins. Once a prepayment has been reimbursed, it starts all over again with a prepayment etc. It is therefore very often that the top of the pyramid finances both the collection side of the trade and the sales/export side when buyers abroad buy at deferred payment terms, something that will be elaborated later on, in section "HS.T.1.3. Payement".


    The larger the population of a country, the larger the quantity of meat that is consumed. Populated countries and meat exporting countries are those that produce obviously the larger quantities of hides and skins. Until fairly recently, the 1950's, the leather industry was mainly concentrated in Europe with hundreds of tanneries in England, France and Italy, hence, to give an example, skins produced in the Indian Subcontinent with a population of  a billion people which produced in the 1980's some 75 million goat and kidskins plus 34 million sheep- and lambskins were processed in Europe. Oceania, and South America with a small population but with a large meat processing industry did not have a domestic tanning industry that could convert all the raw materials into finished leathers, hence also their unprocessed materials went to Europe for tanning.
    This huge trade of hides and skins from one continent to another required the establishment of trade channels which led to the creation of important trading houses. Due to their colonies England and the Netherlands hosted the most important trading houses for hides and skins, whereas French traders concentrated mainly on the north African market. The trading houses operated both as brokers and  merchants and were extremely well organised with excellent communication channels, and a network of agents both at the countries of origin and the countries of destination of the merchandise. These brokers/traders provided also for some kind of guarantee, that ensured that the shipped material was also the contracted material, and that shipped material would be correctly paid. Most of these trading houses had their own offices at major export cities like Dhaka and Chennai, with personnel that checked the quality of outgoing material.
    Improved communications in the second half of the 20th century with telex becoming a common tool, IDD phone service replacing operators at switchboards, telefax, e-mail and now internet phoning, steadily replaced the traditional trading houses and developed direct negotiations between sellers and buyers even without the intermediary of sales agents. Few trading houses are left and those that have remained needed to adapt to the new market requirements and have become merchants who buy for their own account and resell to the highest bidder.


    When air travel was less popular and less accessible the leather trade convened once per year in Paris at the Semaine International du Cuir. For a whole week operators from all over the world met, discussed and traded. The fair was exactly that, a fair, and the most important meeting place in the trade. People arrived from all over the world with large lists of stocks of hides and skins they wished to sell or buy and during the SIC large quantities of hides and skins changed hands. The Semaine du Cuir was THE major event in the business and set the trend and the prices of the trade. It was what we call today a benchmark. The need to meet, show new products and discuss business, fashion, strategies and policies remain and in substitution of the Semaine du Cuir a large number of fairs have emerged in practically all continents. The most important international fairs are Léon (Mexico), Bologna (Italy) and Hong Kong. A host of other more regional fairs are organised in all continents creating the possibility to both local and overseas producers and international visitors to develop their business, gain visibility in the trade environment and update themselves on what's going on in the trade all over the world. Some fairs are specialised, others have a more open approach.
    The international fair calendar can be found at: http://www.intracen.org/dbms/Leather/Events.asp


    In 2000 with the big boom of on-line business  a group of investors spent several tens of millions of dollars and developed a business to business platform for the direct and on-line trading of hides and skins, chemicals, leather, leather goods, accessories etc etc. Unfortunately but predictably the attempt failed. The leather trade and hides and skin business in particular appear not suitable for on-line trading. The leather trade is a commodity trade of a natural product that needs a hands-on approach since each and every single lot that is traded, is more or less unique with its own characteristics. Once the stage of the fully finished product, shoes, portfolio's, garments, etc. is reached, the B2B  becomes a possible alternative to traditional trading. In fact today you can buy leather goods on line from a wide variety of virtual shops, but you can't buy a lot of hides via e-Bay or its competitors.

    HS.T.1.2. - Marketing

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:44:25 AM


    Established buyers and sellers of raw hides and skins have created their own marketing channels and have a range of business partners. Producers in developing countries often have good business to offer, but are not aware how they can enter the market and sell (or buy) their products. Too many times honest operators fall victim to dishonest  operators and lose money and the motivation to continue. The internet is maybe not the best or safest first approach, unless one is capable to institute a dialogue with the to-be partner and separate the wheat from the caf. It is important to try and find out what kind of a reputation the intended business partner has. Embassies and Chambers of Commerce should be able to give a helping hand, although a good agent is better.
    A large number of sales or purchase agents is involved in the raw hide and skin trade. Many of longstanding existence and excellent reputation, who are capable of assisting an emerging business with expertise and marketing experience. Good agents know to which customer they can direct a new producer in order to develop a safe first approach into profitable business for all involved. A good agent is worth his commission!

    HS.T.1.3. - Payment

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:44:47 AM


    The sellers ship goods and issue their invoice to the buyers, who are required to pay depending on the agreement negotiated between the parties. This option has no guarantees to the sellers. The buyers enter in possession of the goods and become thus the legal owners after clearing customs with only a moral obligation of payment.


    This form of payment provides the seller with a document in which either the buyer accepts his debt and promises payment on an established date (D/A), or the bank accepts the to pay the buyer's debt by countersigning the draft (D/P). In the first case payment is not guaranteed as the buyer can refuse to honour his acceptance of the draft, whereas in the latter case the buyer's bank has made an engagement which in fact guarantees payment as the buyer cannot withdraw his consensus for the draft acceptance, provided the bank itself is of course reliable. Payment can be cash or after a predetermined delay, which is usually 30, 60 or 90 days, but can reach 120 or even 180 days from the delivery date, or the date of the bill of lading. The draft, whether D/A or D/P is a legal instrument which gives the sellers the possibility to obtain satisfaction in court in case of non-payment. The D/A draft does not protect the sellers from insolvent buyers, or buyers who file for Chapter 11 or bankruptcy.


    Instead of sending documents directly from seller to buyer, sellers can present the shipping documents through banking channels, a practice required by law in certain countries. This means that the shipper presents to his own bank a set of documents, which contains also the document of ownership (bill of lading), as required by the buyers with the disposition to present the said documents to the bank of the buyers for release of the documents in question against payment of the included invoice according to the clauses of the contract between buyers and sellers. It is to be noted that buyers can refuse to pay the shipper's documents for any legitimate or illegitimate reason and the bank has no obligation towards the shippers for payment in case of refusal of the documents. In case of refusal the bank must hold the documents at the disposal of the sellers, but the sellers will be asked to pay for the service charges of the bank before the bank returns the documents to the sellers or their bank. In case the buyers and shippers agree on a delayed payment, the options are like in the preceeding paragraph "Payment by draft) with the same form of guarantee. According to the legal system in certain countries, companies that file for bankruptcy and who have goods in arrival, even if not paid or with documents still at the bank, become the legal owners of the goods in spite of the status of insolvency. The goods can become part of the assets of the bankruptcy and can be claimed by creditors. In such a case the shippers become one of the creditors.


    This form of payment involves and engages the banking system in a more detailed way. The buyer establishes through his bank an irrevocable means of payment in which the bank engages itself that payment will be effected according to a number of clauses, provided that the by the shipper presented documents are conform to the conditions expressed in the letter of credit. Once a letter of credit has been opened by the buyer's bank in favour of the shipper through the shipper's bank, it can't be revoked until its expiry date. If the shipper presents the by the letter of credit demanded documents in perfect, I repeat "perfect", condition, and within the outlined time limits, then the buyer's bank is obliged by international convention to effect payment of the shippers documents. However if there is even one smallest discrepancy in the presentation of the documents, automatically the buyer has the right of refusal of the documents and hence of payment. In one way a letter of credit is a safe means of payment but it can boomerang on the shipper if the documents are not in order. Documents are studied by banking experts and if there is a discrepancy, they'll find it! In order to safeguard oneself against unreliable banks, one can demand a confirmed letter of credit, which adds the guarantee of the foreign banks correspondent, making the letter of credit more or less failsafe, but it does not protect against discrepancies in documents. The letter of credit protects against a bankruptcy because it is the buyer's bank who guarantees payment, and it's the buyer's bank who become creditors towards their client.  


    As far as shippers are concerned prepayment of a contracted lot of hides and skins is the safest method of delivery, but it does not safeguard the buyer in any way in case the shipper does not deliver or delivers bad quality. The banking system provides for what is called a "red-clause" letter of credit which has all the characteristics of a letter of credit, but grants a cash pre-payment to the shippers, who are obliged either to ship the counter value of the payment or re-pay the pre-paid amount. This method is not failsafe, because in case of bankruptcy of the shippers the bank does not cover the pre-paid amount to the buyers.

    HS.T.1.4. - Incoterms

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:47:54 AM

    "Incoterms" is an abbreviation of International Commercial Terms, which were first published in 1936 by the International Chamber of Commerce (ICC). Since that time there have been six different revisions and updates to the Incoterms. The Incoterms provide a common set of rules for the most often used international terms of trade.
    The goal of the Incoterms is to alleviate or reduce confusion over interpretations of shipping terms, by outlining exactly who is obligated to take control of and/or insure goods at a particular point in the shipping process. Further, the terms will outline the obligations for the clearance of the goods for export or import, and requirements on the packing of items. The Incoterms are used quite frequently in international contracts, and a specific version of the Incoterms should be referenced in the text of the contract.
    Although the Incoterms are widely used and exceedingly handy, they are not meant for every type of contract. Specifically, the terms used in a contract state exactly when the shipper unloads and relinquishes obligation, and when the buyer takes over for carriage and insurance. The Incoterms are not meant to replace statements in a contract of sale that outline transfers of ownership or title to goods. Therefore, the Incoterms may not be of use when looking to resolve disputes that may arise regarding payment or ownership of goods.
    What are some examples of Incoterms? The 13 Incoterms fall into four different groups. These four groups are:

    • Departure (E)
    • Main Carriage Unpaid (F)
    • Main Carriage Paid (C), and
    • Arrival (D)

    Each group's letter makes up the first letter of Incoterm. For example, if your agreement with a buyer calls for the release of goods by the seller to occur at the seller's location, the Ex Works (EXW) Incoterm would be used. This term states among other things that the buyer is to take over carriage and insurance responsibilities at the sellers dock. Alternatively, if the seller were to deliver goods to the buyers dock, including all carriage and insurance, a term from the Arrival group such as DDP would be appropriate. The DDP term stands for Delivered Duty Paid and includes in its definition that the seller will deliver goods to the buyers dock with all carriage, insurance, and duties paid. DDP represents the most obligations for the seller, whereas EXW represents the least.

    Caution must be exercised when using Incoterms because the Incoterms relate to particular modes of transportation. For example, some of the Incoterms deal solely with transport by sea. Terms such as FOB and CIF can be used only for ocean bound freight. FOB, meaning Free on Board, translates to the shipper (seller) having upheld his/her part of the agreement when the goods pass the ship's rails at the port of exit. The receiving party (buyer) assumes risk and costs associated with the goods once they pass the ship's rail in the seller's home port. Due to the specific mention of the ship's rails, an aircraft or other mode of transport could not be used with FOB. For a shipment scheduled for delivery by air, rail, or some other form of transport with the same agreement as FOB one would need to use the Incoterm FCA, or Free Carrier. FCA can include other modes of transportation such as road, rail, interland waterway, and air. Whereas transfer under FOB takes place when the cargo passes the ship's rails, transfer with FCA occurs when delivery of goods has been made at a destination previously outlined by the buying party. (Source: US Government.
    More information at: http://www.iccwbo.org/incoterms/id3045/index.html

    HS.T.1.5. - Pricing

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:48:35 AM

    Hides and skins are a commodity, hence their prices are fixed by "the market", or in better words by offer and demand. The sellers try to get the very highest possible price for their commodity whereas the buyers try to negotiate the lowest possible price. This is obviously a conflict of interest that is resolved by bilateral negotiations. In today's "instant" world a price has a shelf time calculated in minutes when in the past, with the means of communications that were at the disposal of operators, the shelf time lasted weeks, except during the Semaine du Cuir when negotiations between parties were conducted in person. The prices of hides and skins react in exactly the same way as any other commodity whether that is wood, oil, ore, rice, coffee, tea or whatever else. When the demand rises or production reduces, prices increase. If demand drops or production increases, prices decrease.
    There is a very large variety of prices for hides and skins, depending on a number of factors. The most important factor is geography. Each country and in many cases each region of a country has its own characteristics of the hides and skins it produces, resulting in a typical quality that is specific for that area, and the quality determines the price of the commodity compared to hides and skins that are available from other origins. Hides and skins from farmed animals command a different prices from hides and skins produced from roaming animals. The prices are also determined by the age of the animal that provides the hide or skin. A calfskin fetches a higher price per kilo than a bull or cow hide, a kidskin costs relatively more than a goat skin, etc. The flay is extremely important. Properly flayed hides and skins without cuts or holes have a higher value than hides and skins with flay damage. Another factor is the individual seller who applies his own grading and quality standard.
    All the above factors, plus those that are not mentioned, compose a price, and this myriad of prices create a well ordered and balanced overall widewide picture. This picture is totally interactive, because each change in one market causes also changes in other markets. To keep track of this enormous quantity of data there are a number of market reports. Some can be found in trade magazines, others can be obtained against a fee from suppliers.

    HS.T.1.6. - Documents

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:48:58 AM

    It is the seller's obligation to provide for the appropriate and correct documents, which are required by the country of destination. Each country, or group of countries like the EU have their own demands for the presentation of the correct official documents like the health certificate and the certificate of origin.


    The certificate of origin is normally issued by the Chamber of Commerce of the country of origin. This certificate must be signed and stamped by the competent authorities which may be only the Chamber of Commerce alone or with the addition of customs or other institutions like the National Bank. There are different certificates of origins for example for the EU for road transport (Eur1), or amongst Comesa countries, hence when preparing the certificate of origin the shippers must take into account the country of destination. Some countries consider an ocean bill of lading as an acceptable certification of the country of origin. In this case the port of embarkation determines the country of origin, unless of course other certification is at hand.


    Each country, or group of countries like the EU have their own veterinary regulations, that deal with the import of raw hides and skins. These regulations are part of a bilateral agriculture agreement between exporting and importing countries. It is the seller's obligation to provide the buyer with the correct certification that is required by the importing country. Veterinary or health certificates are available with the local veterinary authorities or can be downloaded from the Internet. Some countries do not require particular forms and accept any form as long as it properly states the required data.
    The EU demands its own certificate to be used, called the "Official Declaration". It is to be noted that contrary to the general belief that the Official Declaration can be presented in any of the official EU languages, you have to present the document in the language of the country in which the goods first land, as that is the point of entry into the Union. Even if the final destination of a container of hides is for example Germany, if it lands in Italy, the official declaration must contain the Italian language! In this case to avoid unnecessary bureaucratic hassle, one best presents the certificate in German, Italian and English.  

    The EU furthermore differentiates between hides and skins originating from slaughterhouses that are licensed to export their (meat)products to the EU (A category) and those that are not (B category). Many by-products that result from hide and skin processing are being used for human consumption in the food, cosmetic and pharmaceutical industries and therefore different veterinary certificates are to be used.


    Some countries importing countries demand special certification which may be confined to invoices and packing lists to be placed inside a container for which the shipper has to issue a certificate that they have absolved the demand, or in other cases that a full set of documents must be authenticated by the importing country's diplomatic mission in the country of origin. It is the buyer's obligation to notify the shippers beforehand of such particular demands. The authentication can cause complications when the importing country has no diplomatic representation in the exporting country. One can then either seek an exemption of the demand or revert to a by the importing country recognised diplomatic mission in the country of origin that can do the authentication.


    In the contract between Buyers and Shippers there is a clause that stipulates which party will insure the contracted goods during transport. Insurance is generally covered for 110% of the goods' value. If the shipper bears the obligation to cover insurance, he will have to submit together with all other documents also the insurance certificate. It is important for both buyer and shipper to evaluate in which country the insurance will be covered as this may become of importance in case of damage. For practical reasons one should consider that insurance cover in the country of destination is the most convenient for obvious reasons. Or if the insurance cover is stipulated in another country than that of destination, that the insurance company has their own surveyors at destination. An insurance cover is of vital importance in case of direct damage suffered by the goods, but also for damage suffered by the shipping line or transport company. Many shippers and buyers don't take into consideration, that if a ship suffers damage, the owners of the ship can declare "General Average", which automatically attributes co-responsibility to the owners of the shipped goods pro-quota. In simple words this means that if a ship burns or runs aground, not only can one lose his cargo, but can be called to pay a percentage of the damage suffered by the ship/ship's owners. These cases are extremely rare, but it can happen and it has happened. Hence insurance cover is vital!           
    Covering insurance as early as possible is good practise and even if one is not in possession of important details, insurance can be covered "quovis", meaning that one covers the insurance for the value of the goods, but reserves himself the right to communicate details like the name of a steamer, the number of a container etc at a later stage, but of course before the goods land at the port of destination.

    HS.T.1.7. - Contracts

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Last updated: 24/05/2007 10:49:39 AM


    Purchasing raw hides and skins is a result of bilateral negotiations between a buyer and a seller, which are defined in a sales or purchase contract. Both parties involved exchange parameters of the goods that are being sold and bought. Nevertheless there are a large number of matters that form part of a sales or purchase operation that are not dealt with during negotiations, and which could generate misunderstandings between contracting partners, as they are normally not specifically mentioned. These matters have been attended to by the ruling international contracts, and form the basis of a solution in case of controversies. The international contracts establish certain rules and parameters. Hereunder the ICSHLTA and UNIC contracts are mentioned in alphabetical order. Both are copyrighted, hence their use is restricted. The ICSHLTA and UNIC contracts are different but very similar. Both deal with the same issues but in different ways and seen from a different point of view. There are other public and private contracts, but the aforementioned contracts are by far and large the most important.


    Click on the link provided at the end of this paragraph to download the complete text of the ICSHLTA International Hide & Skins contract in English version in pdf format. This is the 1999 version of the contract. Publication has been kindly permitted by courtesy of ICSHLTA, who are the copyright© owners of the contract. Reproduction is not permitted and publication on this website is only for informative reasons.
    Link: ICSHLTA Int Contract 6.pdf


    Click on the link provided at the end of this paragraph to download the complete text of the UNIC International Hide & Skins contract in English-Italian version in pdf format. This is the 2002 version of the contract. Publication has been kindly permitted by courtesy of UNIC, who are the copyright© owners of the contract. Reproduction is not permitted and publication on this website is only for informative reasons.
    Link: Unic International Hide & Skins Contract English-Italian version.pdf


    Both above mentioned international contracts mention an arbitration clause. It is important to know that a contract is valid for arbitration in case of a dispute only if the contract is signed by both parties, and if a place of arbitration is mentioned. Legally a contract is valid based on the negotiations that precede the contract, but the detailed clauses of the international contracts, which are never mentioned during negotiations do not apply if a signature is missing or the place of arbitration is missing, and arbitration in such a case is not possible. The disputing parties will have to revert in such a case to the normal courts. Arbitration awards are binding but if parties are not prepared to give execution to the verdict, there is no way to implement the arbitration award, other than by court order.


    Note: Please note that all costs and financial calculations are shown as guidelines and as such they will need to be confirmed with the local conditions.

    Many of the process stages have by-products, or waste materials, which are extremely significant as sources of potential extra income and environmental concern. This is an important and continued development as Clean Technology is increasing in all countries, to achieve a sustainable industry in both environmental and economic aspects. The first three stages - pre-tannage, tannage and retannage - are all processes in water solutions, so that the quality of the resultant effluent and its' treatment need to be considered for each operation. Solid waste (or by-product) is mainly from pre-tannage and tannage. Finishing may produce atmospheric pollution from spraying.

    LP.1.1. - Pre-tannage

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 10:50:11 AM

    The principal chemical component in leather is the protein collagen and the pre-tannage operations are aimed to remove other proteins as required and to prepare the collagen chains for subsequent cross-linkage by the various tannages.  
    The first stage in pre-tannage is to restore the original moisture to the skin, which will allow all the subsequent processing to be done correctly. The alkaline chemical treatments, normally as lime, then clean the hide structure by removing some types of proteins and giving a degree of swelling. There is a loosening, or destruction, of the epidermis including the hair. The fibre structure is opened up and fats are partially removed as soaps. After the hair is removed, the alkaline swelling is removed and there is a further opening-up of the fibre structure by enzymes. The hide, or skin, is often call 'pelt' in these pre-tannage stages.


    The variety of shapes and sizes of hides and skins reflect the history and health of the animals themselves. It is a good practice to select similar weight, condition and sizes of the raw material so that the chemical and physical processes can be more uniform and efficient. If this is not done, then some pieces will have too much treatment and others will have too little.


    The object is to restore the hide to its natural moisture content and degree of swelling. There is also the removal of dirt, soluble proteins and curing agents (mainly salt).
    It may be either be done in pits (for pre-soaking dried material), paddle (for careful soaking of delicate skins in long floats) or, more usually, in a drum. The drum speed is low and intermittent. Chemicals to aid re-hydration, such as biodegradable surfactants are often included and slight alkalinity helps to achieve a limited swelling. The salt concentration should not be allowed to fall below 2° Beaumé. Bactericide is needed to avoid any putrefaction damage. Ideal temperature is 26°C and pH 9-10.

    GREEN FLESH OPTION - with a by-product of green fleshings and residual fat

    The mechanical operation of fleshing is an option, for hides, to cut away flesh tissue so that the chemicals in the subsequent operations can penetrate easier. All chemicals penetrate faster from the flesh side of a hide or skin, compared with the grain side.

    UNHAIR (lime) - with a waste by product of hair or wool

    The object is to remove the hair and to open up the fibre structure. This is normally done by lime based, sulphide containing, liquors, in drums or paddles. The drums are slow moving at 2-4 rpm, with intermittent running. The method can also be done by surface application (painting); this is normally on the flesh side, by hand or machine, to leave the hair or wool without serious attack. The grain side is used to obtain a particularly smooth grain, when the hair is completely destroyed. In the main drum or paddle operation, the hair structured is destroyed. Fats are made into soaps and there is strong swelling, or plumping, due to the high alkalinity (about pH 12-13). Temperature of 26°C is ideal, but is not to be above 30°C. A thorough washing is needed when liming is completed, with the temperature 4°C above the liming temperature. This allows better fleshing and smoother necks.
    Liming for heavy leather to be vegetable tanned has an extra day in a weak lime solution. This will increase the opening-up of the structure to permit more filling by the larger vegetable tanning molecules.
    Some sheepskins are not put into liquors for unhairing. They are kept in rooms to produce a controlled bacterial attack. This 'sweating' is used to improve the quality of the wool but does not improve the leather quality.
    As this is the most polluting of all the tannery operations, a lot of efforts have been made to reduce the toxic effects. This includes hair-saving instead of hair destruction, reduced sulphide dosages, recycling and alternative chemicals. Enzyme unhairing is another option being developed to avoid sulphide but some alkaline treatment is still needed to open the fibre structure.

    FLESH - with a waste by-product of fleshing

    The limed pelts are in a swollen state and the cutting action of the fleshing machine is more effective here than in the earlier green fleshing operation. Handling is difficult because of the slippery nature of the limed hides and skins. If limed pelt is exposed to the atmosphere for several hours, there is the risk of damage to the surface by the formation of lime-blast. This describes the formation of calcium carbonate films, when the carbon dioxide in the air reacts with the calcium hydroxide of the lime solution. In practice, it can be minimised.

    TRIM - with a waste by-product of the trimmings

    The cutting action of the fleshing machine blades on hides can cause strings of material, which need to be trimmed to give a clear shape. Skins are cleaner.

    SPLIT OPTION (pre-tanned state) with by-products of splits for further processing or for Gelatine and glue stock

    The final leather has to be as even as possible in thickness although this is not the case in the original hide or skin. The object in splitting is to obtain a more even thickness for processing and a more uniform final leather. Hides are much thicker than skins and need to be split either now, or later, in the tanned state. The grain (top) is levelled by passing the hide across an endless band-knife to an accuracy of a few millimetres; the bottom layer, known as the 'flesh split', is of irregular shape and thickness. Splitting is a skilled operation and needs experienced operators and a well-maintained reliable machine. Although, splitting at this stage is more difficult, and less accurate, than splitting in the tanned state, the advantage is that the tanning chemicals penetrate easier and are absorbed more efficiently.
    Splits are processed separately and should be an important contributor to profitability. Several layers can be produced from an exceptionally thick hide, such as buffalo. However, in such cases, the middle layers are weaker in structure than the outer layers.

    TRIM - with a waste by-product of trimming

    The object is to produce an economic shape for sale or processing further. The grain layer (top split) needs to have any ragged edge cut away to facilitate other machine work, whilst the lower flesh split has to be trimmed to such a regular shape that can have a uniform thickness. Trimming should be to retain, or improve, value. The quantity of trim should be controlled to see that it is not excessive, because it loses potential leather to sell and represents profit. Hides can be kept as whole hides until after tannage, but there can be an advantage if the hide is segmented for some specialised productions; the best quality butt can be processed for one product and the shoulder and/ or belly pieces for other products. In this way, more value is added to the one hide.


    The object of deliming is to remove the strong alkalinity of the pelts by the use of weaker alkalis, and weak acids, so that swelling is reduced. Bates are enzymes and the object of bating is to produce a smooth clean grain and remove non-structured collagen and other proteins. It is done at specific conditions of temperature and pH and continues the deliming. The enzyme action improves the softness, grain elasticity and colour levelness of the leather. The work is normally done in a drum at a temperature of 28-30°C and pH to come below 8.5. The drum speed is faster at 10-12 rpm. Maximum temperature is 35°C for deliming.   

    OPTION OF DEGREASE (sheepskins)

    The object is to remove excess grease from the skins to allow proper processing. The percentage content of natural fat depends on the type and origin of the rawhide or skin. Based on dry material, hides have 2-10%, goats 5-10%, hair sheep 8-15%, wool sheep 20-30% and pigs 30-40%. Processing does remove some of the lower levels and leathers need to have some fat for softness, which is also added later. Gloving and nappa skins can tolerate 5% but the excess in wool sheepskins (and pigskins) needs to be degreased. Surfactants to emulsify the fat have been used in combination with fat solvents, which produce satisfactory leathers but are environmentally damaging. Kerosene has been used with solvent recovery, but is also not acceptable in modern practice. Enzymes are being increasingly used for degreasing together with biodegradable surfactants. Temperature is 35-38°C. 

    Scheme of the phases involved in leather production
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 10:51:28 AM

    1. Beamhouse Operations

    The tanning process begins with beamhouse. Operations of the beamhouse are soaking, liming, fleshing, eventual splitting, deliming, bating and degreasing.

    The first phase, the soaking, consists in washing and rehydrating completely the raw hides. 
    Then, they are unhaired and limed by alkaline substances in liming operation (lime and sulphide). The swelling opens up the fiber structure.
    After fleshing, that removes the unwanted flesh, connective tissue and fat fron flesh side of the hide, follow deliming and bating.
    Splitting can be carried out on limed stock after fleshing, or in wet blue after tannage.
    Deliming has the aim to remove lime contained in the hide whilst bating helps to remove partially non-collagenous proteins and clean the fibrous network of the hide from residuals of substances degraded in liming opertaion. The unwanted hair roots and scud can be removed.
    Bating also improves grain of leather and the subsequent run and stretch of leather. 
    Degreasing removes the excess of grease from fatty skins (sheep, pig) to prevent the formation of insoluble chrome soaps or prevent the formation of fat spews at a later stage.

    Substantially, the purpose of these operations is to increase the amount of water in the hide, remove foreign bodies and loosen the structure. The loosening makes it easier for the tanning agents, fats, dyestuffs and other substances to penetrate into the hide.  In the beamhouse operation the non collagenous proteins are removed from the hide, so is epidermis, hair (liming), globular protein (soaking and liming) and the products of protein degradation (bating). 

    2. Tanning

    In the tanning process the collagen fibre is stabilized such that the hide is no longer susceptible to putrefaction. Tanning more diffusely employed is done whith basic chrome sulphate. It starts by pickling the hide or skin in a salt solution with sulphuric acid to lower the pH of the pelts. Pickling has the aim to allow the penetration of chrome tanning agent in all the section of hide. The pH of pickling bath should be near 3. Then, the treatment with trivalent chromium salts is carried out. The fixation of chromium is improved by the basification done with the addition of milder alkaline substance solution. Vegetable tanning is done with natural tannins, that are water extracted from determinated plants, barks, etc. Before tannage, are excuted pickling and pretannage one after the other. Pickling is made with less acid conditions. Vegetable tannage should start at pH near 3,8.  Pretannage is carried out with syntans in order to reduce the astrincency of vegetable tannins. In this way, the penetration of natural tanning agents proceeds in all the section of the hide.  
    It is applied overall for sole leather production, strap,belt  or for ligth leather destinated to leather goods, upholstery.

    Alternative tannages now receive more attention because of environmental concerns. There have been syntetic tannages, that cover a wide range of organic chemicals, such as syntans, glutaraldhehyde and various polymers. The current interest is to replace chrome tannage. There are " metal free" tannages, that avoid the chromium and other heavy metals but do not produce the same identical character to full chrome leather at present. Chrome tannage remains the prime tannage due to its practical management, competitive cost, the quality of articles produced, high shrinkage temperature given to collagen, and its extreme versatility in manufacturing garments, footwear, upholstery and leather goods. Nevertheless, the use of chrome-free and other heavy metal-free articles is spreading rapidly in some specific areas, and in particular within the automotive sector.

    3. Wet-end Operations

    After tanning, sammying out, splitting and shaving operations are carried out. The object of sammying is to remove the unbound water so that the hide can be split and shaved. When exported, the wet blue is not split, so that the full hide thickness is available for the buyer. Quality is sorted on an agreed basis. Exports may specify particular grades.

    The splitting has the aim to reach a more even thickness for processing. The shaving gives the final thickness adjustment. Then, the tanned leather undergoes four chemical treatments, neutralization retanning, dyeing and fatliquoring,  one after the other.

    The objective of neutralization is to remove strong free acids from the leather by using milder alkaline agents. This weakens the strong positive charge of the chrome leather so that the anionic tanning materials, dyestuff and fat-liquors agents can penetrate inside the section. The degree of neutralizations depends on the type of article to be produced.

    The retannage, depending on the article required, has many objectives. It should guarantee the  filling of the looser structure and good tightness of tanned leather. For corrected grain leather, the retannage should confer to leather buffing, and embossing properties. The full grain must retain the natural elegance., full colour shades from dyeing and an attractive feel from a full handle of the leather.  The choice of the suitable retanning agents and adequated retanning systems depends on the types of articles to be produced and the quality of tanned leather at disposal . It is the main use for the synthetic organic tanning materials, but vegetable tannins, polymeric, resin and mineral tanning agents (chrome included) are also used. The environmental concern for trivalent chrome has affected how this material is used.

    The object of dyeing is to colour the leather as required by the customer. This should be an even colour. The anilin full grain leather should be dyed in full colour shades. The colour should be light fast. The leather is generally dyed with anionic dyestuffs. Health concerns have banned the use of dyes containing carcinogenic aromatic amines.

    The object of fat-liquor is to soften the leather, as required in the product, by lubricating the fibers so that do not stick together on drying. The fat-liquor improves also the resistance to mechanical action. The penetration of the fatliquoring emulsions depends on many factors, such as the type of retannage, the degree of neutralization and the nature od the fatliquoring product. The deeper the penetration,  the softer the leather.  After the final wet-end operations, the leather is stacked on platforms overnight and then undergoes the setting out.

    The setting out  is a mechanical operation that has the object to reduce the water content and to spread the leather out by streching in all directions. After setting out, the leather is ready for subsequent drying.

    The drying has the object to reduce the moisture level to about 8-12%. The principal drying systems are suspension or hang drying, paste drying, vacuum drying, wet-toggle drying.

    4. Pre-finishing

    Pre-finishing operations include  conditioning, staking, eventual dry milling, dry toggling. The conditioning has the object to give the leather a moisture content od 15-18% so that allows uniform mechanical softening.  The moistened leather are piled flat for 12-15 hours to allow the moisture to reach the deepest parts of leather.
    Staking soften mechanically the leather, separating the fibers, which have become attached to each other during drying.  It is important that the moisture content is correct. If the leather has too much moisture, the resultant leather in not soft enough after drying out;  if the leather is too dry, the fibers are damaged by mechanical action.
    Dry-milling is a fast revolving dry drum  and is applied when very soft leather must be produced. It could be for upholstery, garments or very soft nappa for shoes. Dry toggling has the aim to dry out flat the softened leather, from the conditioned levels of 15-18% to 12%. 
    The dried softened leather at this stage, known as crust  is sorted for final finishing or for export.

    5. Finishing

    The object of  the final step in the process is to improve the leather servicability  by protecting it from damage of water, soil and mechanical action. At the same time, it is also improving the cutting area. The finishing should improve the surface appearance and the elegance of leather.  All the individual operations are options according to the finished article and the quality of the crust to be finished. Generally, there are several layers of finish applied and the composition varies between the different cases (base coats, pigmented coats and top coats). Adhesion to the leather and inter-coats adhesion is essential in wet and dry conditions. The flexibility of films has to match the flexibility of leather. The lower films in a finish are more flexible with good adhesion to the base, compared with the upper films. The top coat needs to be the most resistant to mechanical action. The films properties are built up progressively in the finish with different formulations for base, intermediate and top coats.

    There is a large variety of finish formulations, which are mainly water based. There are different  materials, including inorganic and organic pigments, dyestuffs, waxes, feel modifiers, matting agents, fillers, polymers of all types, plasticisers, diluents. They are applied to the leather in several coats; starting with higher rates and ending lighter. These coats is applied  on the leather by spraying machines or roller and curtain coaters in all medium and large production. By using roll-coating machines, toxic emissions and waste reduced. So it is possible to prevent atmospheric pollution. The pressing and ironing are intermediate and final mechanical operations . These operations, carried out a high temperature (80-100°C) confer  a gloss effect to the leather. The straight through heated rollers are preferable for productivity and mantaining leather softness. The hydraulic ram presse use heavier pressure to compress the fiber structure and are essential for obtaining an effective embossing. The final sort has the object to check the quality of finished leathers. They are sorted into different grades. The area of the sorted leathers is mesured, usually electronically.finally, the leather is packed and despatched to customer.


    The environmental impact of leather production
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:26:29 AM

    1. Components of Raw Hides

    During the course of the process, roughly 75% of the original raw hide is eliminated as solid residue (fleshing, buffing, dusting, trimming), solubilized substances (proteins, fat, salts), and water.

    Components of Raw Bovine Hides

    1 ton of raw green salted hide25% collagens (leather)
    10%leather waste
    8% hair
    40% water
    17% sludge polluants

    The elimination of 35% of raw material generates an important quantity of solid and liquid waste, to which we must add the contribution of chemicals employed in the various phases, which remain in excess in the final baths or in the leather not chemically linked.

    2. Input/Output for a conventional process

    Schematically, the figure gives a schematic input/output for a conventional process (chrome tanning) for bovine salted hides per tonne of raw hide worked.

    3. Most common polluting parameters

    How it is possible to see in the figure, the most commonly monitored parameters for setting the requirements for waste water effluent are Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), Suspended Solids (SS), total nitrogen (TKN),, Sulphide (S2-), Chloride (Cl-), Chrome (III), Sulphate (SO42-), Grease and Fat content, pH and Temperature. Total Dissolved Salts (TDS), Absorbable Organic Halogenated Compounds (AOX), Surfactants, Biocides are not as common. The composition of waste water effluents varies greatly between tanneries.

    4. Sources of pollution

    The main sources of waste water pollution are the the beamhouse, then follow the tanning and wet-end operations. The main releases to air are due to the finishing operation, although gaseous emissions may also arise also in deliming and pickling. The solid wastes come principally from hair, fleshing, shaving and trimming. A further source of solid wastes is the sludges coming from the effluent treatment plant also although it is not on-site activity in all tanneries. Fortunately, many of these wasres can be classified as by-products as they may be sold as raw materials to other industrial sectors.

    5. Discharge of salt in the environment

    About 70-80% of total tannery chloride stems from salt used for curing and released in the soaking effluents. The rest stems from the pickling-tanning and to some extent from dyeing process. The discharge of electrolyte in the environment might have a significant effect on both aquatic and plant life, with the most fresh species unable to tollerate even relatively low concentration of electrolyte in the water.

    6. BOD5, COD, TKN, SS Loading

    About 75% of BOD5 and COD load is produced in beamhouse, with the main load coming from unhairing that does not use a hair saving system. A significant proportion of COD (about 45%) and BOD5 (about 50%) load comes from liming/unhairing. In total the beamhouse emissions rise about 90% of total SS. Depending on the techniques applied, hair is either separeted or released together with the effluents of the beamhouse, thus contributing to the COD, BOD5, TKN loadings of the effluent and the subsequent amount of sludge generated in the waste water treatment. If the hair is separeted it can be used in various ways. The majority of tanneries employ a hair-burn system whereby the hair is completely dissolved and released in the effluent.

    7. Sulphide Load

    Sulphide, used in the unhairing process, is hazardous for the mankind and environment. Sulphide solution is toxic. The biggest problem is due to release of hydrogen sulphide gas to atmosphere. Sulphide can be transformed to highly toxic hydrogen sulphide gas during deliming and pickling processes. At concentration above 100 ppm can be lethal.

    8. Sulphate Load

    70-75% of sulphate load is produced in beamhouse and tanning operations. Precisely, about 50-55% of toal sulphate in effluent stems from pickling-tanning and associated washing and samming after tanning. The rest steams from deliming (25-30%), when ammonium sulphate is employed as sole deliming agent and post-tannage operations (dyeing). Likewise to chloride, sulphate is toxic for aquatic and plant life.

    9. TKN load

    The main part of total nitrogen (TKN) comes from the liming process. Deliming, when ammonium sulphate is used as sole deliming agent, generates a significant incresing of TKN load. Beamhouse operations contributes for about 85% as a whole account of the tannery TKN load. Nitrogen has a high oxygen demand and provokates eutrophication. Ammonia nitrogen is toxic to aquatic life.

    10. Chrome Load

    About 80-90% of the chrome in effluents stem from tanning. The remainder comes from the wet-end operations, from stock drainage and wringing. Basic chromium sulphate is the salt normally used in tanning. Chrome oxide and hydroxide are generally found in tannery effluents. They are not toxic in any environmental medium because of their insolubility. In fact, chromium hydroxide has a solubility product of 2,9x10-29. For this reason it remains insoluble in the normal environmental pH range and is not bio-available. Unlike chrome hydroxide, the soluble salts have significant acute toxicity to aquatic species. Once they are absorbed by the hides, the Cr(III) is deeply fixed in the leather and has little or not significant toxicity. As before underlined, in the normal environmental pH range, Cr (III), that remains in the bath at the end of tannage, precipitates as chrome oxide and hydroxide.

    Moreover, the sludges from waste water treatment contain chrome hydroxide . For this reason, in Europe there is an increasing pressure to restrict the application of sludges in agriculture. The reasons for this concern are contamination of soils with chromium, pesticides, etc. Landfill of sludge will become increasingly difficult. The availability of landfills is diminishing and new more restrictive environmental laws have been promulgated. The option is the thermal treatment of sludge, that involves a high consumption of energy.

    11. Influence on environment by usage of vegetable and synthetic tans

    Vegetable tanning increases COD and possibly the phenol concentration. The natural tannins present limited biodegradability. Syntans, used in vegetable tanning and chrome tanned leather retanning, are sulphonated condensation product of hydroxil-substituted aromatic compounds with formaldheyde. Many syntans are hardly biodegradable, whereas other are biodegradable to a great extent. Syntans cause a high COD demand and the degradation products of sulphonated polyphenols are strong pollutants. Residual amounts of formaldheyde and phenol are detected in many products.

    12. Influence on environment by usage of Glutaraldehyde

    Glutharaldheyde, used in wet-white leather production as pretanning agent and in chrome tanned leather retannage, reacts completely with the proteins found both in the hide and in the effluents. For this reason it does not create environmental problems. Glutaraldheyde, probably, influences biological treatment negatively.

    13. Influence on environment by usage of Biocides

    Biocides may be used in the curing, soaking, pickling, tanning and post-tanning processes. Many biocides are toxic for mankind and acquatic life and present limited biodegradability. Halogenated organic compounds have been used for a long time in tanneries and halogenated biocides are still sold. Use of quaternary ammonium compouds is allowed for short time preservation of raw hides. Sodium or Potassium-di-methyl-di-thiocarbamate, used in soaking, is considered to be a less environmentally significant bactericide, due to its lower persistency and toxicity levels. TCMTB can be used in tanning as anti-mould agent. Halogenated organic compounds can be substituted in almost every case, but there are exceptions. One of the exceptions addressed is the dry-degreasing of Merino sheepskins.

    14. VOC emissions (Volatile Organic Compounds)

    VOC emissions comes from finishing operation. A number of organic compounds are directly harmfull to human health or to the environment. Moreover many organic solvents undergo chemical reactions in the atmosphere with formation of photochemical oxidants. Certain halogenated organic compounds are ozone depleting substances. In order to reduce VOC emissions in the finishing process, water-based systems are increasingly favoured over systems based on organic solvents.

    Another option to reduce VOC emissions is the use of low-organic solvent finishing systems. Base coats are generally water-based. If very high topcoat standards of wet-rubbing, wet-flexing and perspiration are required, then solvent based systems cannot always be substituted by water-based systems. In some situations, upholstery leathers for automotive and furniture use are examples of such applications. In order to achieve equal characteristics with low-organic solvent and water-based systems, cross-linking agents for the finishing polymers often have to be used.

    The use of cadmium and lead in pigments is not common in European tanneries; it should be stressed, however, that any use should be discouraged. Certain chlorinated organic compounds are released in soaking, degreasing, fatliquoring.

    15. Surfactants

    Surfactants are used in many different processes throughout the tannery, e.g., soaking, liming, degreasing, tanning and dyeing. The most commonly used surfactant is NPE (nonyl-phenol-ethossylates), because of its excellent emulsifying property and cost-effectiveness. NPEs are degraded only partially in aerobic conditions. They form phenolyc compounds which are highly toxic to aquatic environment. The degradation products are accumulated in the waste water treatment sludge. The International Union of Pure and Applied Chemistry cite numerous references for their conclusion that the toxic metabolites of NPEs including nonylphenol, produce an estrogenic response in a variety of aquatic organisms, resulting in a change in their sexual nature. The main alternatives in the leather industry are alkyl alcohol ethoxylates. The alkaly groups can be branched, but more commonly are straight-chained leading to linear alcohol ethoxylatesor (LAEs) . The LAEs are less toxic compared to NPEs and the biodegradability of LAEs is significantly greater than that exibited by the more common NPEs. The LAEs show excellent detergency, wetting, cleaning and grease removal characteristics but they create moderately stable emulsions. At present, when very fatty sheepskins have to be degreased only NPE can achieve the desired result.

    16. Dyestuffs

    Many dyestuffs are hard to biodegrade. They increase COD, BOD5, SS. The main part of dyestuffs used in tanneries is constituded by azodyes. The use of some of them has been forbidden because they can split, under reduction conditions, into any of twenty-two carinogenic aromatic amines.

    17. Cleaner technologies

    Cleaner technologies are applied for reducing the polluting impact originating from leather manufacture, during the cycle of transformation from soaking to finishing. Then, the cleaner waste water are treated more easily in the effluent treatment plant. The application of cleaner technologies has the aim to reduce the environmental impact, obtain harmful substances-free leather articles and save the consumption of water, through the following actions:

    a) Application of techniques with improved fixation of chemicals to leather
    b) Employ of non toxic and eco friendly chemical or chemicals that can form them by secondary reactions in the leather
    c) Recovering and recycling of pollutants baths

    Cleaner technologies can contribute to reduce the sludges volume coming from effluent treatment plant. Moreover, determinated techniques increase the value of solid wastes, that can be sold in other industrial sectors.

    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:27:10 AM

    1. Desalting by drumming

    Before the beginning of the beamhouse operations, green salted raw hides are desalted. If the desalting is well carried out, it is possibile to remove from hides about 20 % of salt. Consequently, the salinity of waste water is reduced.

    Picture of a desalting Drum:

    To remove excess of salt from raw material mechanically, wooden cage drums are made 4-5 meters in diameter and some 7 meters long, fitted internally with about 30 cm long wooden pegs and driven from the circumference at low speed. When mounted at a slightly inclined horizontal axis, the goods can be loaded at the higher end and will drop out at the lower end. The excess salt will have dropped out through the drum apertures on the way through. Trimming is not always effected. After the weighing, beamhose operations are carried out.

    2. The objectives of soaking

    The first process consist of soaking the hides or skins in water. They re-absorb the water lost after faying , in the curing process or during transport. There is also the removal of, salt, dirt, soluble proteins. The absorbed water re-hydrates any dried inter-fibrillary protein, loosening its cementing action on the fibres. The collagen fibres and keratin cells of the hair and epidermis also take up water amd become more flaccid and flexible. The original condition of natural softness is to be restored. Satisfactory soaking is judged by fell, cleanliness and the absence of salt.

    3. Practice of soaking

    Soaking may be done in paddle (for carefull soaking for delicate raw material in long float) and more frequently in a drum.

    Picture of paddles:

    3.1. Dried hides soaking

    The soaking of dried hides is very difficult and requires more time than wet salted hides. That is due to the sticking of collagen fibres, that is provokated by sun-drying and coagulations of interfibrillary proteins. Generally, the dried hides are pre-soaked in pit. Being hard and horny, they cannot be undergone to rotations in the drum. After this reatment (18-24 hours), the hides are soaked in drum.

    3.2. Fresh hides soaking

    Contrary to all expectation, the soaking of fresh hides is more difficult compared with that one of wet salted hides. During the storage of salted hides, sodium chloride attacks the interfibrillary proteins (albumins, globulynes, etc.). This action makes easier their solubilization and removal from interfibrillar network of hides during soaking. Therefore employ of salt needs during the soaking of fresh hides (about 3% on the raw hides weight).

    3.3. Wet salted hides soaking

    Pre-soaking. Before the main soaking, salted hides require at least two washings with fresh water under mechanical action foe eliminating salt, blood and dirt. The wash float should be changed twice after 30 minutes of drumming. The effect of washing can be followed by observing the color of the wash float. The first wash is brown and appears to have a high content of solubles and solids. The colour comes from blood and from manure. With each change in float it becomes clearer and more colorless. Bactericides is needed to avoid any putrefaction damage. Ideal tenperature is 22-23°C and pH 9-10.

    3.4 Main soaking

    After pre-soaking, the main soaking is carried out. The soaking of wet salted bovine hides (28-30 kg) may be effected according to the following guide-lines (% of product calculated on raw material weight) :

    - Length of float : 200%
    - Temperature : 25°C
    - Non ionic surfactant (80% of active matter) : 0,15 - 0,2%
    - Biocide (Potassium-di-methyl-di-thiocarbamate) : 0,1%
    - Enzymathic product ( proteolytic) : 0,5%
    - Alkaline compounds : 0,7 - 0,9% of products constituded by MgO, 0,2% Na2S, 0,3% Na2CO3
    - pH of float : 10 - 10,5
    - Time of process : 22-24 h
    - Drum rotation : 8 h at the beginning of process, then 10 minutes every hour
    - Drum speed : 2-3 rpm
    - Drum dimension : 4,0 x 4,5 m
    - Load : 13 tons

    The length of process and the conditions required depend on the size and thickness of raw material, the curing method. For example, calf skins require shorter time of soaking than cattle hides.

    4. Activity of bacteria during soaking

    Putrefying bacteria can thrive as soon there is as surplus of water or the curing agent is washed out. Thus, before the hide is suitably flaccid it may become putrid and the soak liquor stink offensively. It also indicates that the bacteria are dissolving the hide away and the resultant leather may show tender or damaged grain, looseness, and lack of mechanical resistance. One of earliest signs of this damage is that the hair slips. For this reason use of eco-fiendly biocides in soaking needs (Sodium- or Potassium-di-methyl-di-thiocarbamate). Speeding up the water penetration in the hides reduces the possibility of putrefaction .

    5. Aids to soaking

    The adjustment of temperature, the use of chemical additives or mechanical actions may increase the speed of water uptake of hide.

    5.1. Temperature

    A rise in temperature speeds up the water penetration in the hides. By increasing the temperature, the interfibrillary proteins dissolve more easily; moreover a decreasing of water surface tension against the hide is obtained. At the same time, by rising of temperature, the rate of bacterial action increases. If the temperature is higher than 30°C, the bacterial growth becomes dangerous, giving loose, empty leather, damaged grain or even holes. In the industrial practise, the soaking is carried out at 24-25°C. When soaking is done at this value of temperature, the bacterial growth may be controlled to safety level by acting on three factors: at least two washings with fresh water before the main soaking, process with a shorter length of time (employ of chemical additives or mechanical actions) and use of efficient eco-friendly biocides. If the temperature value of soaking is too low, an insufficient soaked hides may be obtained. Consequently, the resultant finished leather will be hard, cracky, lacks stretch and will present dirty grain.

    5.2. Chemical addition

    WETTING AGENTS: Detergents are recommended (0,2,0,5% on raw hide weight), particularly if the hides or skins are very greasy. Non-ionic ecofriendly surfactants are preferred. The surface tension at the hide/water interface depending on the fat content of the raw hide and on the presence of surfactant in the solution. Water uptake by hide/skin during soaking is inversely proportional to their fat content.

    ALKALI additions are common, as they tend to loosen the hair and epidermis. They also rise pH value of the soaking bath at the suitable range for improving the activity of enzymatic products. Akali used commonly in soaking are products based on magnesium oxide (0,7,-0,8%), sodium carbonate (0,3%) and sodium sulphide (0,2%) that speeds up the loosening of hair and epiodermis.

    ENZYMATIC products employed in soaking have specific proteolytic action on the interfibrillary proteins. Wet salted hides can be treated with 0,5-1% of such product in a soak bath at pH 9-10. They improve the opening-up of hides and reduce the wrinkless on the neck of hide. When the raw stock show some defects due to bad curing as hair slips, their employ is dangerous.

    SALT: The soaking of dried or fresh hides, that do not contain salt, needs its adding (3% on raw hides weight) in order to promote the dissolving of interfibrillary proteins and speed up the water uptake of the hides.

    6. Fleshing after soaking

    In some countries, the mechanical operation of fleshing is carried out after soaking. This operation cuts away fresh tissue so that the chemicals in the subsequent operations can penetrate easier and the quantities of chemicals (sulphide, lime and auxiliaries) are consequently reduced. All chemicals penetrate faster from the flesh side of a hide compared with the grain side. These fleshings are lime and sulphide free and they may be easier processed in the production of by-products as oil and fertlizers.

    Unhairing - Liming
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:28:28 AM

    1. Objectives of unhairing-liming

    The process has in the same time two principal objectives : the removing of the hair, epidermis and the opening up of the hide structure. The increasing of the reactivity between collagen and chromium salt and many other chemicals costitutes the third objective of this process. Unhairing and liming have a synergic action, in the sense that the first helps also the opening up of the hide structure whilst the second contributes to remove the hair and the keratins degrated by unhairing agents.

    2. Action of unhairing agents

    Unhairing is caused by the breaking of the disulphide bridge of cystine that is a component of keratin. It can be provokated by chemicals, enzymathic products or proteolytic bacteria. By using chemicals, the keratin structure may be partially break down forming a pulp or dissolve completely leading to a clean pelt surface with the assistance of mechanical action on the hides that can suspend the hair sludge and empty the hair follicles completely.

    The Breaking of disulphide bridge of Cystine:

    3. Opening-up of hide and shifting of Isoelectric Point

    The opening up of the fiber network is determinated by swelling of collagen and removing of interfibrillary proteins. In this way the tanning agents, dyestuffs and fatliquoring agents can easily penetrate inside the hides. The increasing of the reactivity between collagen and determinated chemicals is due to the changement of the electric state of the protein. During the process, the hydrolysis of glutaminyl and asparaginyl residues causes the increasing of carboxyl groups number. Consequently, the isoelecric point goes down to lower values.

    4. Chemicals used in unhairing-liming

    The substances commonly used in the industrial practice, as unhairing agents, are SODIUM SULPHIDE and SODIUM HYDROSULPHIDE. LIME is employed for the opening of fiber network. MERCAPTANS that can be considered organic sulphides, are always more frequently used with sulphide and sodium hydrosulphide in ecofriendly systems. They allow the reduction of sulphide and hydrosulphide quantities. In this way, the usage of hazardous chemicals can be limited. AMINES, especially dimethylamine, were used for a long time ago in the American leather industry. It has been some years now that is was removed from the market due to the formation of carcinogenic nitrosamines in the air of beamhouses. Dimethylamine was used in combination with smaller amounts of sodium sulphide. The hides were only slightly swollen and the pelts had a very smooth grain.Unfortunately, today, it is not possible to carry out sulphide free liming-unhairing process. The alternative systems do not guarantee the same quality of leather or the same practical management.

    5. Oxidative unhairing

    Oxidative agents for unhairing have been proposed to overcome the problems with the toxicity and the smell of the sulphide and the sulfur compounds. Unhairing by oxidation with H2O2 in combination with sodium hydroxide presents many limits. It destroys the wood in drums and can be used only in plastic drums. Moreover hydrogen peroxide is not easy to handle because of the heat generated when it is dissolved in water. For this reson the drums must be equiped with efficient refrigerating systems. Hydrogen peroxide is available as 30% or 50% solutions but they are strongly stabilized with hydroquinone or another compound. The grain becomes very clean and uniform in shade and the leather becomes softer due to the oxidative attack of the collagen fiber network.Unhairing, by using SODIUM CHLORITE is not applied, because of the developmentt of ClO2, that is blistering agent.

    6. Enzymatic unhairing

    Enzymatic unhairing is a very attractive option in order to eliminate sulphide in tannery effluent. The proteolytic attack of the hair root and the epidermis is effective only after a preatreatment of the hide with alkali. Alkali swell and slightly decomposes the epidermis, the barrier on the grain and that enables the enzymes to penetrate into follicles and into the papillary layer. Unfortunately, very specific enzymes able to disintegrate only the epidermis, hair roots or root sheets proteins do not exist. The extensive degradation of the root sheet and epidermal proteins is not possible without hydrolysis of the surrounding molecular sheets of the collageneous corium. The small amount of collagenases in preparations of enzyme has time to negatively affect the grain surface. In practise, the hydrolysis amounts to a superficial decomposition of the corium resulting in a mat grain on leather. The opening up of hides is secured by a second liming with lime and soda caustic.

    7. Sweating

    The earliest method of unhairing was "sweating". It is still very occanionally practised on sheep, where the wool is of much greater value than the skins. The soaked skins are hung up in dark, humid rooms in a warm condition of 21-27°C until the wool is loose. Under these conditions bacteria thrive and attack the soft keratin cells of hair and epidermis, resulting hair slip. The skins are held in these sweating stores untill the wool is loose (20-40 hours). If the skins are left too long, wholesale putrefaction will occur and they will be seriously weakened on the grain and in overall strenght and may fall in holes. For this reason sweating is not recommended when the skin itself is of prime value. It is only preferred for Merino type woolskins, where the wool may be fine or very much more valuable than the skin. After the sweating, the skins are usually rinsed in cold water and thrown into lime liquor to stop further bacterial attack and open up the skin structure.

    8. Conventional system of unhairing-liming process

    As it was pointed out before, the most widely unhairing agents used in the leather industry today are sodium sulphide and sodium hydrogen sulphide. In addition, mercaptans are used because they are free from the danger of evolution of sulphydric acid, that is a toxic gas. By using mercaptans it is possible to reduce the amount in liming of sodium sulphide and sodium hydrogen sulphide. The unhairing-liming process is generally done in a rotating vessel such as a drum or mixer in a float containing 3-4% lime hydrate and 1,5 to 3,5% sodium sulphide, depending on the types of hides or skins processed. The unhairing effect depends on the concentration of sodium sulphide in the float. In a short 50 percent float with 0,7% sodium sulphide the hair is completely destroyed. If the float is increased to 100% the destruction is incomplete. Only the hair roots are affected.Removal of the intact hair is facilitaded and the process is referred to as a hair saving process. Hair destruction in a 100% float requires at least 1,0- 1,2% of sodium sulphide. Technical unhairing in a drum requires a longer float , at least 150%. In this condition, in practise 1,5% sodium sulphide or more and 1,0-1,2%of sodium sulphidrate can be generally generally sufficient for a complete unhairing. According the type of hides or skins, the process requires from 14 to 24 hours, at 23°- 25°C. The mechanical movement of the hide during the process rubs off the pulped hairs and helps to free the hair roots from deep within the hair follicle. At the same time, the structure undergoes swelling and opening up. Mechanical action should be gentle to avoid pebbling, e.g. 2 rpm for a 4,5 m diameter drum, running intermittently for 5-10 minutes every hour. The course of liming is influenced by the chemical nature of chemicals as well as temperature, length of float, mechanical action and duration of process.

    8.1. Influence of temperature

    With the increasing of temperature, the swelling decreases and the opening up of hide becomes more intense. At the same time, the loss of hide substance raises. Some solubilisation of collagen happens at 30°C. About 5% of protein is solubilised after 2 days of liming carried out at 30°C. Consequently, a significant reduction of mechanical resistances takes place. Therefore, the temperature of liming bath must not higher than 25°C.

    8.2. Influence of the float length

    At the beginning of process, the length of float strongly influences the quality of finished leather. With the decreasing of the length of float, the swelling decreases. At the same time, the penetration of alkaline substances through the hide is easier and the complete hair destroying happens quickly due to high concentration of unhairing agents. In this way the same pH value is achieved in short time in all the section of hide. When the chemicals are deeply penetrated inside the hide, water is added. The consequent swelling is homogeneous in all the section of hide and it is possible to obtain a spready leather without accentuated wrinkles. Therefore, it is useful to begin liming in short float and after the complete penetration of alkaline substances, the float must be lenghten.

    8.3. Influence of mechanical action

    Mechanical action of drum makes easier the penetration of chemicals inside the hide and therefore quickens the achievement of uniform pH value in all its parts. Consequently, as pointed out before, swelling is more homogeneous and unhairing happens quickly. Mechanical action should be gentle, e.g. 2 rpm for a 4,5 m diameter drum, running intermittently for 5-10 minutes every hour. Continuous rubbing of grain on the drum walls should be avoided. In this phase, the plump and swollen grain is particularly weak; therefore it could be heavily damaged (blind grain). Furthermore, due to friction, the continuous running could cause too high temperature.
    Sometimes, when particularly delicate hides are processed, liming is carried out in paddle.

    8.4. Extension of process duration

    The extension of liming duration promotes the opening up of hide structure. Moreover, the elasticity of finished leather is improved while the mechanical resistances are made worse. In addition, the hydrolysis of glutaminyl and asparaginyl residues is intensified. Therefore the fixation of chromium to hide during the tannage is augmented.

    9. Environmental impact due to unhairing-liming process

    Beamhouse operations, particularly the liming process, make up the most consistent part of total pollution produced, due to its considerable contribution in the chemical and biological oxygen demand (COD, BOD5), total nitrogen (TKN) and sedimentable solids (SS). Moreover, the effluents coming from the liming bath at the end of operation have a high content of sulphide. Approximately, liming-unhairing process constitutes 50% of total pollution caused by all the cicle of leather manufacture.

    Pollution produced by the entire processing cycle

    10. Strategies to be applied to reduce the Liming Pollution

    The hair saving process, final bath recycling, employment of reduced quantities of sulphide and sulphydrate represent clean technologies in order to reduce the pollution due to conventional unhairing-liming operation.These strategies, that is, the use of specific reducing substances, the application hair saving process and the recycling-reuse of liming bath, can be combined together. Thus, it is possible realize processes which enable both a reduction in sulphide, to the benefit of workers' health, and simultaneously reduce environmental pollution.

    11. Toxicity of Sodium Sulphide and Sulphidrate

    Sodium sulphide and sulphydrate, both fundamental chemicals in the liming process, are unfortunately toxic for the environment and for mankind. Special regulations must be respected for these products, in stocking and safety measures above all during the deliming phase, where there is a real risk of developing sulphydric acid due to the action of acidic substances. Sulphydric acid can be lethal if it exceeds certain concentration levels. Sulphide is also a problem for waste water: it poisons fish if reaches the environment directly.
    The problems due to the using of sulphide are the following:

    - Possible development of sulphydric acid (toxic gas)
    - Poisons fish
    - In certain concentrations inhibits the waste-water bio-degrading capacity of bacteria
    - Formation of large quantities of sludge in chemical-physical treatment

    On the other hand, the liming process using lime and sulphide presents a series of indisputable positive properties (as well). Through the use of lime, an adequate opening of the fibrous structure of the hide is easily achieved, resulting in suppleness and the desired character of the leather. Sulphide and sulphydrate guarantee a safe and complete unhairing action. The risk of residual hair is negligible.

    12. Possibilities to reduce the sulphide and sulphidrate offer

    It is not possible to completely replace sulphides at the present time, but it is possible to reduce strongly the quantities used by combining and employing auxiliary agents of various chemical nature. The employ of Mercaptoethanols and Thiourea dioxide (THDO) contributes to minimize the use of sulphide.

    12.1. Mercaptoethanols

    Mercaptoethanols, employed in present industrial systems, react with keratin by way of a mechanism that is similar to that of inorganic sulphides. These substances are oxidized very easily through the action of oxygen in the air. Their rapid oxidation is therefore advantageous for the quality of waste- water; their complete oxidation at the end of the unhairing process leads to the formation of non-toxic chemical compounds. Furthermore, mercaptoethanols cannot generate sulphuric hydrogen during beamhouse operations, specifically in deliming and/or pickling, phases during which hides come into contact with acids or substance with an acidic reaction. Due to their costs (+40%), and greater quantities required compared to sulphide (about 50% more to obtain the same unhairing effectiveness), these compounds cannot completely replace sulphide, but can be employed in combination with the aim of reducing quantities of traditional liming agents, proving advantageous in terms of the environment and safety standards for the health of tanning operators. Hides obtained from treatments using these products are flatter than those ones produced by employing of sulphide. As mentioned previously, they oxidize easily, and their reductive power can be partially inhibited already during the liming process, yet another reason for which they must be employed together with sulphide.

    12.2. Thiourea dioxide

    Thiouea dioxide (THDO), in an alkaline environment, provides excellent unhairing, to the point of completely replacing sulphide. The hair remains intact, and its recovery contributes to lowering COD in sludge water. The best characteristics of this compound are the cleanliness and uniformity of colour resulting on hides treated with it. Thiourea dioxide is capable of exercising a heavy bleaching effect. Unfortunately, its high cost inhibits the complete substitution of traditional unhairing agent, but it can be conveniently employed in parts of 0.5%, allowing for a significant reduction in quantities of sulphide.

    13. Continuous hair-saving liming processes

    These processes have been rediscovered during the past decade, for environmental reasons. It is applied on cow hides and skins where the hair is not of high value. The paint unhairing is a special type of hair-saving system that is used for sheep skins, where the wool is of great value. It is a discontinuosus system unlike the modern methods that are effected, outside the drum, through a continuous filtering of the hair from the liming bath, after its loosening. The liming bath is continuosely recirculated during the liming process untill the intact hair is completely separated.

    Continuous hair-recovery plant :

    The paint is usually a solution of sodium sulphide at concentration between 8 and 20% (8-15°Bé) thickened with an equal amount of hydrated lime. The paint may be hand applied using a brush resistant to the paint chemical. The skin is best laid out flat on a wire mesh table, hair or wool down. The painted skins are piled until such time as the wool loosens. Woolskins may be paired flesh to flesh, stacking the pairs 1 meter to 1,2 meters high. Too high piles may lead to overheating due to bacterial activity from dirt on the wool, the heat being retained by the exceptional insulating properties of the fleece. Temperature in the pile of over 30°C will cause grain damage and skin weakness. After piling, wool is pulled and graded, usually by hand. Hair is scraped off with a curved, blunt unhairing knife on the beam or by an unhairing machine.

    14. Advantages of continous hair-saving processes

    As we pointed out before, the essential advantages provided by a continous hair-saving processes are a drastic reduction in COD, BOD5, total nitrogen (TKN) values of effluents and a significant contraction of the sludge volume, coming from waste-water treatment. The hair, which contains high quantities of proteins and nitrogen, can be used as a biological fertilizer in agriculture and horticulture. Reducing these parameters renders achieving legislative limits less difficult, and allows for the cutting down of depuration costs. The COD value, referring to the final liming bath, with the destruction of hair (hair burn process) and hide washing water before fleshing, represents 55-60% of the COD figure for the entire beamhouse phase, including tanning and post-tanning operations.

    This is a very high value which can be cut down using hair saving techniques. At the same time, the heavy reduction in quantities of sludge, whose treatment or dumping is one of the tanning industry's greatest problems, allows for an easing of the situation while awaiting decisive technological developments.

    The other hair saving liming systems, aside from the method using unhairing painting, today not applied in Europe, are: the Darmstadt method and the Sirolime process, that is the first system proposing a continual filtration of hair from the bath. These methods, differently from that one currently applied in the practise, are not based on the partial immunization of hair. Processes employing the partial immunization of hair are the safest, and are now commonly used in tannery.

    15. Complete hair immunization

    Complete hair immunization (including the root of the hair) can happen if the hides are treated with strong alkaline substances, for a time long enough, before the addition of unhairing agents. In this case, the cystine disulfide bridges, a structural element of the hair keratin, are transformed into thioethers. A compound is formed called lanthyonine. This substance is no longer hydrolyzed by the reducing action of sulphide, as shown in Figure, and the unhairing process is arrested.

    Formation of lanthyonine with alkaline treatment (immunization) :

    16. Selective Hair Immunization

    The immunization of hair must be selective. The immunization of stem must occur quickly, while the root must remain sensitive to the hydrolytic action of the sulphide, following the treatment using alkali, and thanks to a reaction that is slower in this area. The subsequent addition of sulphide or sodium sulphydrate provokes a reduction of keratin disulfide bridge at the root of the hair, causing unhairing. The hair stem just about unaffected by liming agents, and can be recovered for filtration continuously in the bath. The opening of the hide structure is obtained by the subsequent addition of more lime and small quantities of sulphide and/or sulphydrate. The latter compounds also serve to remove short hair and residual epidermis.

    However, this system, generally based on the initial adding of lime, can run into problems of incomplete elimination of hair and epidermis if pre-treatment times with alkali are excessive, or when the lime dosage is too high. Under non-optimal working conditions, there is thus a risk that the immunization process proceeds down to the root.

    If work conditions are properly respected, the process produces good quality hides and is therefore often applied in industrial practices.

    17. Controlled Hair Immunization

    The problem linked to the possible immunization of the hair root was resolved with the development of the system defined as "controlled immunization," described by Christner.
    The difference lies in the fact that at the start of the process, istead of adding lime, a mercaptoethanol is used which is sulphide free, generally at 20% active substance, and is well known with reducing and hydrolytic properties. Before the immunization phase, this agent penetrates down to the hair root, whose pre-keratin structure is thus partially attacked. Through the addition of lime, after a limited time, we obtain the immunization of the external part of the hair.
    Subsequently, using limited quantities of strong reducing agents such as sulphide or sulphydrate, we obtain a loosening of the hair within 30-40 minutes. The hair, just about intact, is thus separated from the bath by filtration. The bath is then lengthened, with lime and sulphide being added to obtain the structural opening of the hide and eliminate any residual hair. Perfectly limed hides are obtained using this technology, which is much safer compared to the methods described previously.
    Basically, the main points for this process, based on controlled immunization, can be described as follows:

    17.1. Dispersion of Mercaptoethanols

    The reducing agent (1.0-1.3% of mercaptoethanol on the weight of the hides) penetrates inside the hide until the root of the hair; the pH value of the bath is included between 9,5 and 10. At this pH value it is not capable of reducing the hair stem keratin, but begins to attack the pre-keratin at the root.

    17.2. Immunization and Activation of reducing activity of mercaptoethanols

    Lime is then added (1.0%-1.5% on the weight of the hides). The pH value rises to 12.0-12.5 and the reducing activity of the mercaptoethanol consequently increases, as it begins to decisively hydrolize the pre-keratins of the root. Under the influence of lime, the immunization of the hair stem is obtained in a time of 90 minutes.

    17.3. Removal of Hair

    At this point, sodium sulphydrate is added (0.9%), which further reduces and hydrolizes the pre-keratin. In this phase, the loosening of hair is achieved. Contrary to the previous method, even a prolonged treatment with lime, before the addition of sulphydrate, does not entail the risk that residual hair will remain. The well-preserved hair is thus separated by filtration.

    17.4. Structural opening of the hide and removal of residual hair

    The lime bath is lengthened, adding lime (2.0-2.5%) and sulphide (0.7-0.9%) to obtain swelling, the opening of the fibrous network, and the removal of residual hair.
    If the hair were removed from the bath at the end of the liming process rather than immediately after the loosening phase, the COD values for the waste water would be 8-10% higher. Using mercaptoethanol, we can simultaneously bring down the COD, TKN, purification sludge and sulphide concentration present in the lime waste water.

    Principle of controlled immunization :

    18. Recycking of Liming Bath

    Bath recycling further cuts down on pollution from liming, with a reduction in water and chemicals used during the process. What's more, hair recovery significantly cuts down on protein contents in lime baths destined for recovery.

    By combining bath recycling and hair recovery, drastic decreases are registered in values for COD, BOD5, sedimentable solids and concentrations of sulphide in waste water. At the end of the process, the waste bath is sent to the recovery plant which, in its most widespread version, generally comprises:

    - a filtering system (1) which catches large solid particles in suspension contained in the bath at the end of the liming process
    - a homogenization basin (2) into which the liquid is pumped after the primary filtration
    - a conical trunk container (3) in which the sedimentation of the bath coming from the homogenization basin takes place
    - a pumping system (4) capable of transporting the sludge, separated at the bottom of the decanter (3), to the sludge treatment process
    - a rotating filter (5), whose filtering material, is a compact bed made up of fossil meal, capable of withholding even small particles contained in the liquid coming from conical trunk sedimentation unit
    - an accumulation tank (6) from which the bath is sent to the drums

    Liming - Bath Re-cycling Plant :

    If the operations are carried out correctly, the re-cycling liquid maintains a constant composition. It must be analyzed before use, and is reintegrated wit fresh chemicals directly during the liming process. Generally, savings in sulphide, lime and sulphydrate amount to 20-25%. The accumulation tank (6) features a heating system for maintaining the recycled bath at a temperature of between 22 and 25°C, depending on the season of the year.

    The homogenization tank (2) is equipped with a mechanical agitator which inhibits the sedimentation of the sedimentable solids. The natural fat extracted from hides during the liming process surfaces at the top of this tank. It is eliminated by flotation and collected in a flotation chamber.During the liming process, it is important to add a certain quantity of white water into the re-cycling bath, in order to maintain a constant volume, since it is difficult to collect the bath completely; 20-30% of the bath remains in the drum. The volume of liquor collected must amount to a value slightly greater than 100% of that employed at the start. This slight excess serves to compensate for the loss in volume caused by the separation of suspended solids during sedimentation phase.

    19. Conclusions

    Tests on various batches of hides, produced at an industrial level using liming techniques with reduced offer of sodium sulphide, bath recycling and hair recovery, failed to show significant differences between hides produced in subsequent cycles, neither at a qualitative level nor in terms of mechanical-physical resistance. Tanners have long known of the positive effects on the quality of hides from the reusing of old lime baths; this is due to the fact that the solutions in these baths also contain aliphatic amines deriving from degradation reactions on proteins. These compounds allow for a less aggressive liming process and an improved opening of the fibrous structure. The result is a leather with a softer feel and a finer grain.
    The cost of the installation of plants to recovery the hair and recycle the liming bath is quickly paid off by saving money in the effluent treatment and for chemicals in liming process.

    Example of liming process with bath recycling and hair saving system on green salted bovine hides
    (Drum speed: 3rpm) - % referring to the weight of desalted raw hides:

    In a traditional liming process, carried out on wet salted cow hides, the quantities of sulphide and sodium sulphydrate employed are on average respectively 2,5% and 1.0% of the weight of the raw material. For processes making use of mercaptoethanol, hair saving system and re-cycling of exhausted liming bath, there is a drastic reduction of these two compounds (1.0 % for sulphide, and 0.8% for sulphydrate).

    20. Lime Blast

    Lime blast is due to precipitated calcium carbonate on the surfaces of hides or skins. It is formed by reaction between Ca(OH)2 in the skin and CO2 in the air, on leaving hides in piles exposed to the air before and after the fleshing operation or by reaction between Ca(OH)2 and the hydrogen carbonate ion coming from temporary hardness of water. Leaving limed skins stationary in drums with water containing hydrogen carbonate must be avoided. Lime blast is first visible as harsh white areas but later, after dyeing and drying, may develop it as coloured stains.

    21. Fleshing

    The mechanical operation of fleshing has the objective to cut away flesh tissue so that the chemicals in the subsequent operations can penetyrate easier. All chemicals penetrate faster from the flesh side of a hide or skin, compared with the grain side. This operation is carried out generally after liming process. The limed pelts are in a swollen state and the cutting action of the fleshing machine is more effective than in the earlier green fleshing operation. Handling is difficult because of the slippery nature of the limed hides and skins. The handling necessary for fleshing, executed after liming, interrupts a possible complete system of drum processing : soaking, unhairing, liming, washing, deliming, bating, pickling and tanning which could be automated using modern plant Only one loading and unloading would be necessary from raw hide to wet blue. Unfortunately, in the case of most hides, quantities of flesh, fat or connective tissues on the raw hide give rise to significant inequalities in depilation, swelling, etc., and it is considered essential to flesh before subsequent processing which would compound this fault. Consequently, attention is being given to green fleshing, i.e. before soaking but the major problem is that the variable length of hair on the grain side gives varying pressure between the feed roller and the cutting cylinder, resulting in clean fleshing down the butt and little fleshing on the bellies where rhe hair is less dense.
    The fats contained in fleshing can be separated for marketing and the protein degradate produced at about 30% water content. The latter has been used as a component of animal feed.

    The cutting action of the fleshing machine blades on hides can cause strings of material which need to be trimmed to give a clear shape. Skins are cleaner.The trimmings can be used for the production of glue.

    22. Splitting

    The object of splitting is to obtain a more even thickness for processing and a more uniform final leather. Hides are much thicker than skins and need to be split either now, or later, in the wet blue state. The grain is levelled by an endless band-knife to a few millimeters; the bottom layer, known as the "split", is of irregular shape and thickness. It is a skilled operation and needs experienced operators and a well maintained reliable machine. Although, splitting at this stage is more difficult and less accurate than splitting in the tanned state, the advantage is that the tanning chemicals penetrate easier and are absorbed more efficiently. Moreover splitting on limed hides gives a slightly higher surface yeld than in the wet blue state. Splits are processed separately and can become an important contributor to profitability.

    Deliming - Bating - Degreasing
    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:29:15 AM

    1. Objectives of deliming

    After liming, the hides are swollen, show pH values between 12,0 and 12,5 and contain inside its fiber network chemicals as lime and sulphide, that must be removed before the tanning. Moreover, substances coming from the degradation of proteins, during the liming process, are contained in the hides. Deliming and bating, carried out in the same bath, have the objectives to remove lime and sulphide, adjust pH value between 7,8 and 8,5 and purge the fiber network of collagen. In the same time the lowering of pH value causes the reduction of swelling. Consequently, an adequate separation of collagenic fibers is achieved. At last, the enzymatic action of bating agents contributes to remove partially elastin.

    2. Washing before deliming

    The washing removes the unsolved lime from the surface of hide e partially that one phisically absorbed between the fibers of collagen. The Ca++ ion, that is chemically bound to carboxylic groups of collagen, is not eliminated by a simple washing. However, washing causes some reduction of hide swelling.

    Prolonged washing are dangerous. If the water supply is hard and contains soluble calcium and magnesium bicarbonates or carbon dioxyde dissolved in it, these react with the lime. A fine deposition of calcium carbonate is formed, commonly known as lime blast. This affects the feel of the grain and also causes stains on the leather after dyeing. For this reason, soft or softened water is to be preferred. Warm water (30-35°C) reduces the plumping of the hide. Consequently, the access of water inside the fiber network occurs easier and the lime is removed in a more efficient way.

    3. Removing of Calcium Chemically bound

    Calcium that is chemically bound is removed only by using acidic compounds. Deliming agents are constituted by acidic compounds, that is weak organic acids or acidic salts The acid costant dissociation (Ka) of these compounds must be greater than that one of carboxilic group of collagen. Also some weak acids that possess a complex-former capability towards Ca++ ions, can suitably be employed. The elimination of calcium and alkalinity from the hide cause a reduction of osmotic swelling. The water, that has been produced swelling, goes out in the deliming bath. A suitable deliming agent must be able to form soluble calcium salts.

    4. Degree of deliming

    When soft articles must be produced, as upholsthery, garment or nappa shoe upper leather, a through-deliming should be carried out. The hides, destined for footwear classic articles (e.g. box-calf), that must show the characteristic springy-handle, do not require a through-deliming operation. In this case, one third of the section will contain lime at the end of the operation. It will be eliminated by following pickling. The desired degre of deliming depends on many parameters: the dosage of deliming agents, the lenght of process, the chemical nature of deliming agent, the thickness of hide, the intensity of washing carried out before the deliming. The penetration quickness of the deliming agent depends also on the lenght of the float: in short float, the diffusion of deliming agent inside the hide cross-section is quicker, but the solubilization of calcium salts formed during the process is more difficult. Generally, very short floats are adopted (30-40% of water on limed weight) when full thickness heavy hides are processed. The adding of small quantities of ammonium sulphate, because of its buffer capacity, makes easier the through- deliming. During the operation, the lenght of float increases: 60-70% of water, calculated on limed weight, because of the decreasing of swelling, leaves the hide and goes to the bath. The correct pH range of deliming process is included between 7,5 and 8,2, while the temperature of the bath must not be below 32°C.

    5. Deliming agents currently used

    At the current state of the art the following types of deliming agents are used:

    - Deliming agents containing ammonium salts
    - Deliming agents low in ammonium salts ( based on organic acids)
    - Deliming agents free from ammonium salts (based on organic acids and boric acid)
    - Deliming agents based on organic esters

    6. Performances of efficient Deliming Agents

    The deliming agents, that are used in the practise, should present the following characteristics:

    - An adequate deliming value
    - A satisfactory buffer capacity
    - A fast through-deliming time
    - A high lime solubility value
    - An eco-friendly behaviour
    - An acceptable price-performance ratio

    6.1. Deliming Value

    The deliming value informs about the quantity of deliming agent (expressed in grams) required to neutralise 1g of calcium hydroxide. The deliming value of strong inorganic acids are between 1,3 and 1,5, those of organic mono and dicarbonic acids between 1,5 and 1,8 and the widely used ammonium salts and organic esters have values around 1,8 and 2,2. As far as the price/performance ratio is concerned, everybody should in fact, use hydrochloric or sulphuric acid for deliming. Both are unexpensive and have a good deliming value. On the other hand, however, it is generally known that they cause more or less pronounced acid swelling during deliming and will not permit proper through deliming. While the deliming value, informs us about the quantity of deliming agent to be used, it tells nothing about the actual performance of this particular product.

    6.2. Buffer Capacity and Through-delimining

    The degree of through-deliming of different deliming agents as a function of time on unsplit thickned pelts (6-7 mm) depends on the chemical nature of such substances. Ammonium salts are fastest in through-deliming. Products free from ammonium salts need a rather time of almost 3 hours. Deliming agents low in ammonium salts and based on a balanced mixture of ammonia or ammonium amd organic acids are at least 30% faster.

    The fast deliming action of ammonium salts results from their acceptable and overall from their excellent buffer cacacity.

    Time requirement for through-deliming as a function of the buffer capacity:

    A surplus of ammonium ions combines with the developing ammonia to an optimum buffer system.
    The ammonia reduces the plumping effect.

    6.3. Buffer Capacity and Swelling

    If strongly inorganic acids are used all by themselves, e.g. hydrochloric acid, sulphuric acid., the buffer effect is nil, or rather much lower if organic acids, e.g. formic acid, lactic acid, etc., are used instead of ammonium salts. The consequence of a poor buffer effect are acid swelling and fixing of the scud. Therefore, the sole use of such systems cannot be recommended despite their good deliming value. Boric acid, which is normally used in combination with organic acids in products free from ammonium salts, also increases the buffer effect. If we check the course of the pH value in deliming with a short float, we note that if products from ammonium salts are used, the process occurs for a prolonged period of time in the critical range of pH 5 and below.

    From this pH range onward the scud can fix itself on the grain surface and there is the risk of acid swelling. An absolutely critical point is reached at pH 4,0, where pronounced acid swelling occurs. With products low in ammonium salts the pH value never drops below 5 and a gradual approach is made to the neutral range. In the case of ammonium salts and organic esters with their pronounced buffer effect, the minimum pH value is 8. The lower the pH value of the deliming liquor, the more toxic hydrogen sulphide is emitted.

    6.4. Lime Solubility Value

    The deliming process must not be associated only to the neutralisation of the pelt acidity. As the name of the process implies, it must also remove the lime or calcium that is deposited in the capillaries and that is ionically bound to collagen. Thus, a good deliming agent ought to transform calcium hydroxide of the pelt in an easily water-soluble salt. The precipitation od salts within the fibers must be prevented, as they form sulphuric acid, for example, ammonium sulphate, citric acid, bisulphites and borates.
    Therefore, in the case of unsplit material, when deliming is carried out with ammonium sulphate, the calcium content of the pickled pelts is higher compared with that one showed by hides delimed with deliming agents, that form water-soluble salts. Most of residual lime in the form of calcium sulphate is found in the centre of the cross-section of the hide. When wet-blue has been obtained by deliming the hides or skins with ammonium sulphate, the higher residual calcium content in the pelt centre result in an higher chrome content in the centre split that in the grain split. The irregular distribution of chrome might be one of the reasons for the loose grain of leather obtained from pelts delimed with ammonium sulphate. The situation is quite different for the split pelts. In this case, the pickle effects a kind of final deliming. Consequently the residual calcium is evenly distributed throughout the hide and the differences of chrome distribution in the cross-section of the hide is negligible.

    6.5. Ecological Behaviour of different Deliming Agents

    Ammonium NH4+ produces many difficulties in effluent treatment plants. Moreover, it is a strong poison for fish, has a substantial oxygen demand for the nitrification (NH4+ » N2) and causes an eutrophication of the waters by nitrogen fertilisation. By looking at the distribution of the ammonium load in the beamhouse operations, it is easy to understand that a reduction only makes sense in deliming and bating. Systems free from ammonium salts give a minimum value of nitrogen, due only to the protein load.

    7. Conclusions

    Then, deliming and bating agents low in ammonium salts cause a considerable reduction of the effluent load. Therefore, we can draw the following conclusions:

    - The sole use of the fast and gently deliming ammonium salts, marked by a favourable price/performance ratio, will become ever more difficult for ecological reasons
    - Moreover, ammomium salts have certain negative effects on the properties of the leather, such a causing a loose grain
    - Organic esters are an alternative to ammonium salts which comes close to the deliming effect of the pure ammonium salts and guarantees the right pH conditions
    - Deliming agents based on organic acids/boric acid have a little buffer capacity and are slow in through-deliming. Therefore, they should not be used alone but always in combination with strongly buffering compounds.

    8. Alternative Deliming System: Deliming with Carbon Dioxide

    The introduction of CO2, as deliming agent in the industrial practise, presents some difficulties. Particularly, when full thickness heavy hides are processed. Really, the through-deliming requires very long time. On the other hand, the good quality of leather obtained with this technique, the cheap cost of the product and overall the environmental advantages reached with this process are important factors that urge many researchs in order to solve this problem. CO2 dissolves quicly in water. Its solubility depends on temperature and pression. Naturally, low temperature and high pression help the solubilization of carbon dioxyde. It is introduced in the drum through the hollow axle in the gaseous state. Carbon dioxyde reacts with lime and forms calcium bicarbonate, that is soluble in water:

    Ca(OH)2 + 2 CO2 = Ca(HCO3)2

    If the pH of the deliming bath is higher than 8,2 can be formed calcium carbonate, that is insoluble in water and causes the formation of lime blast on grain side. Therefore, the pH control of the bath and all the hide cross- section is very important. Deliming must be carried out in a pH range included between 6,5 and 7,0 in order to avoid the formation of calcium carbonate. The lower pH, compared with that one reached in the conventional deliming system, does not affect significantly the activity of pancreatic enzyme in the course of bating. The activity drop is higher with regard to bacterial proteinases.

    Compared with the conventional system, this technique, that is carried out at lower pH, generates higher amounts of sulphidric acid. This problem happens overall at the beginning of the process. An oxidation of sulphide with H2O2 before the adding of CO2 is sufficient to avoid this heavy inconvenient.

    S2- + 4 H2O2 = SO42- + 4 H2O

    9. Objectives of bating

    Bating has the objective to cause an enzymatic hydrolysis of non-collagenous components, that are contained in the hide or skin after the unhairing- liming operations. Indeed, at the end of this operation, residues of epidermis and hair, that is entraped in the hair bulb, proteoglicans, a part of globular proteins and natural fat are still contained in the hide. The removal of these residues, provokated by enzymatic action, is necessary to clean the grain side of the hide. In addition, bating has the objective to remove partially the elastin, that is a protein, in order to obtain a satisfactory elasticity of grain. If the elimination of elastin is excessive an empty and loosed grain leather is obtained. The increasing of the grain elasticity improves the mechanical-physical properties of leather (tensile strength, grain resistance, etc.). The softness of leather is also emphasized.

    Enzynatic processes have to be controlled very carefully. Action of bating baths may be dangerous , as their prolonged action, overdosage of preparations may cause an excessive removal of proteins from the pelt; due to this it may become spongy or empty, and the layers may become separated (loose grain). Collagen is resistant to the proteolytic enzyme activity. If, however, the nonhelical parts of the molecule are removed, an irreversible loosening of the fibril structure may occur. During bating operation, the helical region of collagen must not be absolutely damaged to avoid heavy grain defects. Such problems can be emphasized, when slight putrefaction actions, due to an uncorrect curing, are already being carried out on the raw hides or because of an excessive opening up of hide stucture operated by liming operation.

    10. Origin and Properties of different Enzimes

    The bating agents are constituded by enzyme misture: they are on the market under concentradet form or mixed with sandwust and ammonium salts. Therefore, a commercial product may contain large or little amounts of inert material. For this reason, the enzyme activity is judged by the capacity to digest casein and expressed in Lohlein Volhard Units. It is possible to find on the market weak bating agent at 500-1000 units for shoe upper leather on calskin and strong bating agents at 1.500-2.000 units suitable for glove leathers or chevreaux. Generally, enzymes derive from vegetable, bacterial or animal sources. The animal enzymatic products are widely used in bating process. They are extracted from the bovine pancreas and for this reason they are named pancreatics enzymes. A classical pancreatic enzyme is principally constituted from trypsin, chimotrypsin, elastase, lipase, amylase, carboxipeptydase. Tripsyn and chimotrypsin hydrolyze the non-structured proteins, lipase and amylase decompose respectively fats and proteoglycans.

    The leather, obtained from hides treated with pancreatic bating agents shows excellent fullness, grain tightness, finer grain, colour-levelness while the softness is lower than that one obtained with different tipes of bating agents. In addition the usage of pancreatic enzymes guarantee a higher safety

    Infact the employ of bacterial enzymes may be dangerous because they, in certain conditions, can attack the collagenic structure. Consequently, blind grain can be originated. It has been demonstrated that the hides treated with bacterial enzymes release an amount of hydroxyproline , three times higher compared with that one released fom hides treated with pancreatic enzymes. Hydroxyproline may occur in other proteins but in uncomparably smaller quantity compared to the quantity present in the collagen.

    The pancreatic enzymes have also a higher lypolytic action, therefore they allow the homogeneous fat distribution in the cross section of hide.These evidences show that the pancreatic bating agents preserve collagen from dangerous hydrolysis reactions.

    11. Parameters influencing on Enzyme Performances

    During the bating operation, important parameters are temperature, pH value, the quantity of bating agent employed and the lenght of process.
    The right value of temperature to achieve an excellent enzyme activity is comprised between 34°C and 37°C. Below 32°C, the decreasing of the enzymatic activity is significant. Above 40°C, heavy damages of hide structure are procured.
    The highest enzymatic activity of pancreatic bates is showed in the pH range between 7 and 9. The bating operation is carried out at a restricted range of pH between 7,8 and 8,2. On the market there are also bating agents that show the maximum activity in acidic medium. They are used in the bating of the hides arriving to tannery in the pickled or wet blue state. In these cases, bating is carried out to eliminate the folds, that have been formed during the prolonged stockage or when the hides have been bated not enough in the original tanneries.
    The quantity of bating agent used and the length of operation depends on many factors such as liming intensity, compactness and weight class of raw hides, softness degree and grain tightness that we want to give to leather. Generally the hides, that have been undergone a strong liming, are treated with smaller quantities of bating agent. The concentration and the length of process must be arranged each other: the amount of bating agent employed in a 30 minutes process could be excessive in a 50 minutes bating. An exaggerated bating generates empty and loose grain leather. Usually, in the bating of heavy hides for sole leathers or other vegetable tannages, the quantity of bating enzymes necessary and the extent of the bating action is very little, for the hide has been well limed and most of the protein degradation products have been removed. The liming operation for side leather is not so extensive as that of sole leather, and a slightly stronger bating action is needed for it than for a sole leather. In the harder natured goatskins, higher concentrations of bating agent are used and the bating proceeds for a much longer time.
    The action of bating is stopped by producing conditions unsuitable for the enzyme activity, the easiest systems being to cool the hides down 18°C. It is achieved by adding cold water in the drum till to reach this temperature. It is desiserable to wash out the chemicals and the degradation products from the bating application and to lower the temperature to stop the action of the enzymes .

    12. Objectives of Degreasing

    Degreasing is the last step in the beamhouse operations. Incomplete removal of fat may be the reason for nonuniform tanning and dyeing and gives rise to grease stains. Degreasing is carried out in the same bath of the deliming and bating operations. In the production of calf skins and cow hides, the fat contained in raw material becomes saponified by liming ioperations and washed out by the simple use of surfactants.

    13. Degreasing Agents

    Before we pointed out that the more diffused degreasing agents today are based on NPE (nonyl-phenol-ethossylates), because of its excellent emulsifying property and cost-effectiveness. NPEs are degraded only partially in aerobic conditions. They form phenolyc compounds which are highly toxic to aquatic environment. The main alternatives in the leather industry are alkyl alcohol ethoxylates. The alkaly groups can be branched, but more commonly are straight-chained leading to linear alcohol ethoxylatesor (LAEs) . The LAEs are less toxic compared to NPEs and the biodegradability of LAEs is significantly greater than that exibited by the more common NPEs. The LAEs show excellent detergency, wetting, cleaning and grease removal characteristics but they create moderately stable emulsions.

    14. Degreasing of Greasy Skins

    Differently from calf skins and cow hides, pig and sheep skins contain after liming still over half of their fat content. Natural fat occurs in sheep or pig skins sometimes in large proportions spotwise until to 50% by weight of the hide mass and that fat is very uneven distributed in the skin area At present, when very fatty sheepskins have to be degreased only NPE, among all the emulsifires, can achieve the desired result. But it is indeed not possible to remove simple and sufficient complete greater amounts of natural fat with nonionic detergents. Nonylphenolethoxylates act better than fat-alcohol-ethoxylates and the amount to strip from the pelts is only about 50% of that amount being present in the pelt. It can be concluded that complete removal or distribution to an uniform level of the fat content in the pelt needs some repeats in new float with new addition of emulsifier and always followed by extended washings. In any case elevated temperatures are necessary to liquidify the solid fat. A slightly pretanning, e.g. with glutaraldehyde, is made to stabilize the fiber structure and this allows to degrease at 45°C.

    Pretanning with Glutaraldehyde to improve the degreasing efficiency of pickled sheep skins - % referred to picled weight:

    15. Degreasing with Organic Solvents

    The natural fat, present in the sheep and pig skins, can be removed most effectfully by dissolving it with organic solvents together emulsifiers. These compounds ( trichloroethylene, kerosine, etc.) are not use today because of their polluting effect. After their use, they must be recovered from the bath by distillation and from the skins by pressing. Howevver, this system is difficult and not economic.

    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:29:43 AM

    1. Objective of pickling

    Pickling has the objective to prepare hide or skin for tanning. Soaking, liming, deliming, bating have all been concerned with the removal of unwanted components. At the end of the pickling operation the hide or skin is theoretically a purified network of hide protein. On this hide fibre can now be built the chemical rections which will produce the desired character of the leather. The pickling operation is carried out by using organic (formic acid) and inorganic (sulphuric acid) acids in presence of salt.
    Chrome tannage fixes to the leather more rapidily and strongly the higher the pH of the skins. The acid provokates the blocking of aminic groups and the decreasing of carboxylic groups ionisation. Consequently, a decreasing of the reactivity of chromium towards the collagen is caused. Decreasing of reactivity promotes the even penetration of chrome inside the hide or skin, therefore a fine and resistant grain is obtained. Thus if the skin is pickled to a low pH of 3,2 one gets a mellow light chrome tannage and if to a pH of 4,5 one may get rapid surface fixation with little penetration and almost raw skin inside. In the practise, generally, pH of the skin in all the section, is included between 2,8 and 3,2.

    2. Pickle method

    The hides or skins are paddled in the salt and water until the salt has dissolved and diffused evenly. The sulphuric and formic acids are slowly poured into ten times its volume of cold water. The acid solution is added to the bath in the running drum. The hides are then runned 2-4 hours, depending on their thickness, to obtain through penetration. The acidity of the pickled hides may then checked and may be corrected by further additions od acid if required. Generally, pckling will give a pH included between 2,8 and 3,3, depending on the types of hide/skin or articles. The pH desired will depend also upon the tannage to be used. There is ample salt present not only to prevent acid swelling, but to cause some decrease in thickness of the skins, which are now white, soft and flaccid. Swelling may be avoided if the the density of the pickling bath is at least 6° Bé. It is necessary to check the salt concentration on the volume of water and the acid on the weight of skins, as the acid is adsorbed by, and chemically combines with, the skin. Non-swelling acids, based on naphtalin-sulphonic acid derivatives, can replace the conventional acids in pickling . These compounds in spite of a strong acidity do not cause the swelling of hides. When they are employed, the use of salt is not required. In this way, it is possible to reduce the amount of salt in the wastewater. Unfortunately, non-swelling acids are too expensive and give hard leather. Therefore, they are used only in restricted cases, when it is absolutely necessaty to reduce the quantity of salt in the effluents.

    3. Pickle parameters

    Mostly, when full thickned cattle hides are processed, pickling is carried out by using short floats (30-50% of water). Thus, the through penetration of the acidity is quicker and the quantity of salt to be usecd to reach 6°Bé is less than in longer floats. The amount of acid used in the pickling operation to reach a wanted pH value, depend on the depth of deliming, the thickness of hides or skins. The acids are added in the drum slowly to avoid too sharp changes of pH. So, weak acid, that is formic acid, is added in the drum before before sulphuric acid. At the end of the process, the temperature of the bath must not be higher than 25°C, to avoid unwanted hydrolytic actions generated by the reactions of acid against the hide protein. Therefore the hides or skins must be cooled at the end of bating. It is advisable a slow rotation of drum to avoid the formation of blind grain and the increasing of temperature.

    4. Check of pickling

    When heavy cattle hides are processed, the section of the backside and half back must be completely passed from acid. It means that the section of these parts appear yellow when they are checked with bromo-cresol green. In this situation, the basic chrome sulphate will pass also through the most thickned parts and the splits obtained by splitting operation will be tanned perfectly in all their section. In the past, hides or skins remained owernight in the pickling bath, today the major part of tanneries, also if they process heavy cattle hides, prefers to proceed with the tanning, as soon as the backside of hide is through-passed by acid.

    5. Pickling of hides destined to vegetable tannage

    Vegetable tannage may be done on pickled skins. Where strong pickling is undesiderable, the bated or delimed hides or skins may be further acidified down to pH 4,0-4,5 either by naturally occurring weak acids in old tan liquor; the addition of weak acids, e.g. 1% acetic acid; or by the use of slightly acid syntans in the absence of salt because such acid syntans may be classed as non-swelling acids, although they also have a slight tanning action.

    6. Pickling on cattle hides full thickness for upholstery

    % referred on fleshed weight
    (3-4 r.p.m.)

    LP.1.2. - Tannage

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:30:21 AM

    Tannage is the irreversible conversion of the natural fibre network of pelt into the material leather. The collagen structure is permanently cross-linked. This makes it resistant to bacteria, putrefaction and higher temperatures. When dry, it does not feel hard and can normally be rewetted.

    PICKLE - (can be option to export from this stage)

    The object is to prepare the pelt for tannage, or for export, by adjusting the level of acidity in salt solution. This controlled acidity is needed to allow penetration of tanning materials through all the thickness uniformly and to combine correctly. If this was not done, the tanning materials would react too strongly on the outer layers, not penetrate deeper and the appearance of the surface would be damaged. The leather would also not be tanned correctly.
    The pickle is varied according to the type of tannage to be made, with less acid conditions being used for vegetable tannage. However, salt concentrations are increased and essential to avoid any acid swelling. 6% salt on the total volume of water is a safety level for the most acid conditions. Temperature must not exceed 28°C.
    Vegetable tannage should start at pH 4, chrome at pH 3 and the export pickle needs to have a stronger pickle in terms of acid content (absorbed by the pelt) and a preservative to prevent mould. This pH is below 2. Storage is good if the pickled pelts are kept cool, below 32°C air temperature.


    The object is to convert the pelt into leather by creating a more stable structure, which will not putrefy and maintain an attractive appearance. The options are:  

    • Chrome tannage is the most widely used and most important tannage, in more than 80% of leathers. This is used in the production of shoe upper, furniture upholstery, clothing, leather goods and gloving leathers. Basic chromium sulphate is the main chemical, penetrating at pH 3 in controlled stages and being fixed at pH 3.8-4.0. Process starts at about 24°C to finish at 39°C for better chrome exhaustion. The higher end temperature is achieved by increasing the drum speed from 5 to10 rpm. The leather will have a shrinkage temperature of 95-100°C. The cross-linkage is identified as being made with the carboxyl groups of the collagen. The process is done in a drum and takes about 10 hours for hides; skins are tanned faster because they are thinner. The colour is blue and it is often exported semi-finished as 'wet blue' with the use of preservative. Environmental protection is limiting the amount of trivalent chrome salts in an effluent for discharge into a public waterway, because the heavy metal affects the treatments in the waterworks. This has resulted in many developments to reduce the levels of chrome in effluent by increasing chrome uptake in the drums, and by various recycling methods. There are also ecological concerns that the trivalent blue chromium salts in leather could be converted into the carcinogenic hexavalent state, with its danger to health.      
    • Vegetable tannage uses material obtained from parts of certain plants. These may be the bark, wood, fruit, root or leaf of the plant. The chemical compositions are complex and are mixtures of natural polyphenolic compounds. The shrinkage temperature is 70-85°C. The characteristic colour varies from pale yellow-brown to an intensive red-brown depending on the type of vegetable tanning material or mixture of tanning materials used and the application conditions. The nature of the materials limits the light fastness, and there is a considerable change in colour with time and exposure to sunlight. They have high molecular weights and probably form linkages due to a combination of hydrogen bonding and their size. The resultant leather is therefore, much fuller and heavier, than chrome-tanned leather. Vegetable is the original tanning method and used for heavier, more compact leathers from hides - sole, strap, belt, bag, harness, upholstery - but it can make soft light leathers such as linings and leather goods - particularly from skins. The process is slow, with limited mechanical action from pits or slower running drums. The time is about 4 days for lighter weight leathers and 12 days for sole leathers. The temperature normally starts at about 20°C for penetration, increasing later to 35°C. It has been largely replaced by chrome tannage, which is quicker and more economical.
    • Alternative tannages now receive more attention because of environmental concern. There have been synthetic tannages in use for many years, known as syntans. These cover a wide range of organic chemicals, such as phenols, naphthalene, glutaraldehyde and various polymers. This is a drum process and takes about 10 hours, similar to chrome tannage, but at temperatures of 25-30°C and pH 3.0-3.8.  The shrinkage temperature of the leather produced is 70-80°C. It was originally used to make speciality leathers, such as white, and to replace part of the established tannages. The current interest is to replace chrome tannage and 'wet blue'. There are 'wet white' tannages for export and for further processing in the same tannery. These avoid the chromium but do not produce an exactly identical leather character to full chrome leathers at present. However, the auto-upholstery buyers are demanding 'chrome-free' leathers and such supplies are expected to increase. The colour of the leathers is white, or yellowish, and they have very good light fastness.  These leathers are limited to drying temperatures of 40-50°C, compared with 70°C for chrome tanned wet blue. 
    • There are also many pre-tannages which are used to follow the pickle, but before the main tannage, so that there is an improved uptake or performance from the tannage itself. Such examples are formate before chrome tannage, phosphate before vegetable and syntans before 'chrome-free' tannage of wet white.  

    After tannage, leathers contain a lot of surplus tan liquor. Consequently, this excess is normally allowed to drain, with the leathers piled on a 'horse' or stacked on platforms, overnight. This allows further fixation of tanning material by the leathers whilst the drained liquid is collected, for recycling or for treatment in the effluent.


    The object is to remove the unbound water so that the hide can be packed, split or shaved, with consistent uniform moisture content and an exact thickness. The natural differences in the structure of the hide mean that the tanning material absorption and the liquid absorption also vary. Consequently, the leather is still not the same thickness all over after tannage, even if it was already levelled by splitting in the pelt. It is first sammed to reduce the water content from about 70% to about 60%. The hides are then squeezed between the moist felt rollers of a samming machine, which also flattens the shape. A setting out action, to further spread the hide, is often incorporated into the sequence on the machine, with extra rollers. The moist leather is then sorted for export or for further production in the tannery.


    This refers to cutting the hide into two halves and is done now, if it was not done before tanning. It may be done manually with the use of a cutting guide on a table, or by specialist equipment. It has to be accurately done down the backbone to produce the flatness in that area. Hides can also be cut into other shapes if required in the final leather.

    SORTING - (can be an option to export at this stage)

    The object is to grade the hides, and skins, according to their potential quality. Wet blue (or wet white) is normally exported without splitting, so that the full hide thickness is available to the buyer. Quality is sorted on an agreed basis. This will assess the degree of damage in the hide, or skin, and how it affects the cutting value. Each quality has a different value.
    Exports may specify particular grades. The wet leathers for export need to be carefully folded, and packed in plastic sheeting so that the packing is completely waterproof. This is to prevent permanent creasing of the leathers and any drying out in transit. The rewetting of such dried leathers is extremely difficult, and it is advantageous if a very small amount of a hydrophilic compound (fat-liquor type) can be added to the tannage, provided there is no effect on final quality.  
    If it is not for export, a similar sorting is done for the tannery's own operations. This has the same assessments, and produces a range of qualities. Sorting also decides whether it can be full grain leather, or whether the grain needs to be buffed away and corrected in some way to disguise faults. The sorting figures are then compared with outstanding customer orders. Their requirements will show thickness, quality and quantity. In this way, the actual customer orders start from here, and should have a reliable completion date for a delivery schedule.

    SPLIT OPTION - (tanned state) producing a split for further processing and tanned waste by-product

    The object is to obtain a more even thickness for processing and a more uniform final leather, if it were not done in the limed condition. At this stage, the leather has a more stable structure. The tanned hide is less swollen and so it is easier to handle. The actual levelling is more accurate. The thickness is determined by the final product to be made. It will allow for some final adjustment by shaving. The machine and operators are critical to a successful operation, from quality and profitability aspects. A good machine is a valuable investment for the tannery.

    TRIM - with by product of damp tanned leather waste

    The object is to produce an economic shape for sale or processing further. The grain layer (top split) needs to have any ragged edge cut away to facilitate other machine work, whilst the lower flesh split has to be trimmed to such a regular shape that can have a uniform thickness. Trimming should be to retain, or improve, value. The quantity of trim should be controlled to see that it is not excessive, because it loses profit. The actual flesh split is larger than a flesh limed split.

    SHAVE - with by product of tanned shavings

    The object is to make the final thickness adjustment and have an even cutting through leather with consistent moisture. The moisture content should be 30-45% Splitting leather can never be accurate enough and so a shaving machine is needed to refine the produced thickness and leave the flesh side smooth. The shaved thickness is determined by the customer requirements, allowing for the loss in processing between the semi-moist condition and the final despatch.

    PREPARING LOADS for retannage and dyeing

    The object is to plan the production of crust leather to meet the demands of the customers' and sales forecasts.  Customer orders define the quantity and quality of finished leather. The tannery identifies the type of retanned leather (the crust), which corresponds to the finished leather. If there is not sufficient quantity and quality available in crust stock, there has to be more produced from the wet blue. In this way, the work tickets from the wet blue are planned to supply the crust stock as required, from orders or sales forecasts. The loads will be in standard sizes for the retanning drums and correspond to established processes.   

    Contributed by: Mr. Sammarco, Umberto
    International Consultant,

    Last updated: 24/05/2007 11:33:12 AM


    Tanning is a process of converting unstable raw hides into leather, with adeguate strength properties and resistance to various biological and physical agents. From a chemical point of wiew, tanning is the introduction of additional crosslinks into collagen, which bind the the active groups of the tanning agents to functional groups of the protein. According to the various types of tanning processes, the tanned leather will achieve a series of properties:
    - Higher hydrothermal stability
    - Higher resistance to the action of chemical agents
    - Higher resistance to the action of bacteria and proteolytic enzymes
    The tanning leads also to a changement of the appearance and of the handle or feel of hide or skin. It becomes rougher, it looses the trasparency on drying. In comparison to the wet state it shows in dried state a certain reduction in flexibility bur instead of that a certain porosity.


    According to the kind of crosslinking, that they form with the protein, the tanning agents can be classified in three different principal groups:

    - Mineral tanning agents (chrome, alluminiun, titanium, iron salts), that form co-ordination bonds with the collagen. Their fixation is mainly on the acid groups of the protein

    - Synthetic and vegetable tans. They form with the collagen electrovalent, hydrogen bonds and dipole forces. Syntans and vegetable combine with the basic groups of the proteins, and with the peptidic groups of the collagen. 

    - Aldehydic tanning agents (formaldehyde, glutaraldehyde, oxazolidines, phosphonium salts ecc.) they form covalent crosslinks with the protein. At higher pH's the aldehydes combine with unionized amminic groups of the collagen.


    Every tanning process is based on two fundamental phases:
    - Penetration of the tanning agent inside the fibre weawe of the collage
    - Fixation of the tanning agent and formation of crosslinkages

    A rapid tan fixation give a poor rate of tan penetration and vice versa. The homogeneous distribution of tanning agent inside the hide is achieved if, at the beginning of tannage, its reactivity is slow towards the collagen. When, the complete penetration is achieved, the parameters values (pH, temperature, ecc.) are arranged to increase the reactivity and allow the fixation of tanning agent to the protein. The conditions to be adopted are different, in according to the chemical nature of tanning agent.

    In the mineral tannages low pH's (2,8-3,2) will give penetration and rapid fixation is caused by higher pH's (3,8-4,0), whilst rapid fixation of vegetable tans is favoured by acid conditions. The behaviour of aldehydes is similar to mineral agents. In the last case, a satisfactory fixation is obtained at pH near 7,0.The vegetable tannage, begins at pH 4,0-4,2 in presence of syntans(pretanning agent).  At the end of the process, pH value is lowered  and the fixation is improved.


    Vegetable tannage could be considered as dehydration of hides, replacing the water molecules  by a sheath of natural tannins molecules. After drying, the vegetable tanned leather absorbs water easily enough. The amount of tan employed can varies fron 20 to 50% depending on the type of raw hide and article. The vegetable tanned leather shows a relatively firmer grain and light brown colour of various nuances depending on the type of natural tan used.  Usually, the colour of leather darkens under the action of light. In opposition to the current opinion, this tannage gives some environmental problems. There is the conviction that the vegetable tannins are not polluting compounds only because they are extracted from natural sources. In reality, their biological degradation is very difficult and the effluent treatment is expensive.
    Sole leather, determinated types of upholstery leather, leather goods, lining, mechanical leather, bookbinding leather are produced with this tannage.


    5.1. Chrome tannage

    Chrome tannage is the prime tannage due to its practical management, competitive cost, the quality of articles produced, high shrinkage temperature given to collagen, and its extreme versatility in manufacturing garments, footwear, upholstery and leather goods. The dehydration effect of this tannage and the quantity fixed is less than with vegetable tannages  and therefore the hardening on drying is more pronounced. After drying, the chrome tanned leather absorbs water less easily than the vegetable tanned leather. Invariably, some type of fatliquoring agent is applied to the wet fibres before drying. Chrome tannage gives a soft green-blue leather, with an excellent dyeability and higher mechanical-physical properties compared with other types of tannages. Generally, 6-10% of basic chrome sulphate (25% Cr2O3, basicity: 33,33%, refered to the lime hides weight)) is employed as tanning agent.  The chrome tanned leather shows a good lightfastness.
    Nevertheless, chrome tannage presents environmental and toxicological problems. For this reason, metal-free leathers have been attracting increasing interest in the last few years.Over the last 30 years leather technology literature has been dominated by ways to reduce the environmental impact of leather production and techniques to reduce the discharge of chromium reagents have been a significant element in these endeavours.

    5.2. Aluminium tannage

    Aluminium tannage gives harder and more compact leather compared with that one obtained by chrome tannage. The aluminium salts are less fast to precipitation with alkali. The aluminium-tanned leather shows a low hydrothermal fastness and it is easily detanned by a simple washing with water. The aluminium tanning agents more commolly used are Kal (SO4)2.12 H2O, alumimium sulphate and basic aluminium chloride.
    Generally, the amount of tanning agent used is included between 1,5 and 2,5% expressed as Al2O3.  White lightfast leather is obtained by aluminium tannage. Today, aluminium tannage, with certain exceptions (glacé gloving leather, furskin) is not applied in the industrial practice. The effluents containing aluminium salts are toxic for fish.

    5.3. Zirconium Tannage

    Zirconium tannage gives white lightfast leather. The feel of zirconium-tanned leather is too hard. When it contain high amount of zirconium, it shows a good hydrothermal stability. To this purpose, it needs to offer to the hide an elevated amount of zirconium salts equivalent to 10% of ZrO2, referred to the fleshed weight. Zirconium tannage is expensive. The tanning process must begin at very low pH values (1,8-2,0) because of the aptitude of zirconium salts to hydrolise easily. Zirconium does not give particular environmental problem. Zirconium compound are employed in tannery mostly in the retannage of chrome-tanned leather when suede has to be produced or for nubuck article.

    5.4. Titanium Tannage

    Titanium tannage has been introduced on 1920. Howewer, the leather obtained by this tannage is white, light fast but too hard compared with the chrome-tanned leather.  The titanium-tanned leather takes over an orange colour when it is retanned with natural tannins.

    5.5. Other Tannages

    There are many chemicals that will react with hide collagen. They are not use extensively in practice for reasons of cost, danger in handling, difficulty of application or control required to obtain a suitable hand on the resultant leather and for other problems. Mineral salts have been considered (e.g. iron, silica), quinones, synthetic polymers, di-isocyanates, sulphonyl chlorides. 


    Today, the term wet white indicates a leather that has been pre-tanned only with organic substances and can be easily shaved. After shaving, this product is tanned with vegetable and synthetic tannins, and usually includes synthetic polymers and various auxiliaries of a different chemical nature. The finished leathers are chrome- and heavy metal-free, and their shrinkage temperature is approximately 80°C. The resulting leather is defined as metal-free (MF).
    However, it should be clarified that this technology cannot replace the traditional chrome tanning process for the production of most of leather articles.
    This aim is not conceivable in the near future due to quality limits of chrome-free articles when compared with chrome-tanned products. The chrome tanning processes based on partial replacement of chromium, are more realistic. Consequently, in addition to the metal-free tanning, that complies with the request of a limited range of leather utilization, the research must be direct towards the improvement of the chromium fixation, by its using only in the retannage phase on the precedently metal-free pretanned hides. Nevertheless, the use of chrome-free and other heavy metal-free articles is spreading rapidly in some specific areas, and in particular within the automotive sector, for a series of reasons.

    6.1. Advantages of Metal-free Leather

    By the end of 2015 the European Union will introduce regulations requiring 95% of components from disused vehicles to be recycled. Leathers that are metal-free degrade more easily than chrome-containing ones, and it is known that under the action of light and/or heat the chrome in leathers can be oxidised to chromium (VI). In normal use, natural tannins can stop this transformation thanks to their chemical nature and this has been confirmed by studies carried out by influential researchers. Consequently, both the mechanisms of chrome tannage and ways to avoid this reaction are now better understood. But the problem has not been completely solved yet.
    Moreover, the disposal of processing wastes such as shaving, buffing and trimming wastes and sludges, is another inconvenience deriving from chrome tanning. Common incineration causes environmental problems, so these wastes must be disposed of in carefully controlled ways. In the near future pre-tanning with chrome-free substances will reduce the quantity of chrome-containing wastes, and the use of basic chrome sulphate will only be allowed in retanning.
    Other advantages are offered from leathers tanned with organic substances. When subjected to accelerated ageing tests under high temperature and low relative humidity, higher shrinking resistance and dimensional stability are found compared with chrome leathers. These properties are fundamental for automotive upholstery leathers, and particularly where leathers are used for trim, and especially for covering automobile dashboards. But we must consider that metal-free leather when subjected to ageing tests carried out under conditions of simultaneous high relative humidity and temperature will be completely destroyed. 
    The most widespread form of accelerated ageing test consists of exposing leathers to high temperatures and high humidity values in turn. Each cycle lasts 11 hours for a total of 30 cycles. In these exaggerated conditions, the superficial shrinking of the sample must not exceed 10% of the original area. The different dimensional stability of chrome- and metal-free leather samples subjected to temperature of 120°C and relative humidity 100% are shown in Figure.

    Contraction of differently tanned leathers under high heat and relative humidity

    6.2. Disadvantages of metal-free leather

    Compared with chrome leather, wet white leathers are less stable to storing, are more complicated to shave and present a bigger difference between shaving thickness and finished thickness. However, the most critical aspect of wet white is its easy biological degradation. The transportation and storage of leathers in this intermediate state in hot weather conditions is very difficult and could be compared with the relative trouble free properties of chrome-tanned leathers. The biological stabilisation of wet white is, therefore, the most important aspect of metal-free leather production. For the time being, the production of metal-free leather should be considered as limited to fully processing - from soaking to crusts - as a single-site operation. This problem can only be by-passed by the development of an intermediate dry white product. In this case leathers would be easily transportable and storable even in hot weather conditions, ready for wetting back.


    Glutaraldehyde has become the major pre-tanning agent within metal-free leather production. When compared with alternative pre-tanning systems, glutaraldehyde avoids many toxicological problems, and produces good leathers with excellent light-fastness, and good resistance to heat. Among other aldehydes, glyoxal has many limitations, and formaldehyde, although giving fairly good results, cannot be used due to toxicological reasons. Isocyanates and epoxy resins that produce covalent bonds. Similarly aldehydes are used seldomly.
    However, oxazolidine A or I (4,4- dimethyl-1,3-oxazolidine), oxazolidine E or II, and THPS are possible. Oxazolidine A is very reactive and provides a shrinking temperature of approx. 85°C, dependent upon the pH at the end of pre-tanning. Oxazolidine E is less reactive, and gives a shrinkage temperature of approx. 83°C at pH 7.5-8.0.
    Leathers treated with oxazolidine E in combination with vegetable tannins, differ from those pre-tanned with oxazolidine A, being softer and lighter-coloured. THPS provides a shrinkage temperature of approx. 75°C at pH 4.5-5.0. But both oxazolidine and THPS hydrolyses at pH > 7.0 and form formaldehyde.

    7.1. Preliminary Beamhouse Operations

    Experience shows that the essential points for the production of good quality wet white-and fulfilling the numerous requirements of car manufacturers-can be met by attention to the following details: Soaking and liming are carried out as in the production of wet blue.Deliming must be complete so that the glutaraldehyde can penetrate easily through the whole skin section. The use of totally ammonium-free deliming agents involves serious difficulties in deliming in depth, but agents based on ammonium salts cause a yellowing of leathers pre-tanned with glutaraldehyde. Their use, therefore, must be limited when producing pastel shades. It must also be taken into account that bating agents often contain a certain quantity of ammonium salts in their blends. Skins should therefore be thoroughly washed at the end of deliming and bating to remove all traces of ammonium salts.

    7.2. Pickle

    The pickling process has a great influence on the penetration of glutaraldehyde through the leather section. The pH value must be lower than 3.0 throughout the whole section to enable an even distribution.

    7.3. Pretanning with Glutaraldehyde

    The pre-tanning stage plays a fundamental role in the production of metal-free leather. The parameters influencing the process include: 

    The Concentration of the Pre-tanning Agent

    An offer of 0.5% glutaraldehyde at 100% active ingredient produces a leather with a shrinkage temperature of approximately 720C. This is suitable to guarantee correct shaving. A higher offer of glutaraldehyde would provide a certain increase of Ts, but then the tensile strength and tear strength would decrease as shown in Panel.

    In addition, there would be an increase in leather yellowing, causing problems when processing leathers for dyeing in light shades.

    The pH  at the end of Pre-tanning 

    The reactivity of glutaraldehyde with the pelt increases with rising pH. Accordingly, the shrinkage temperature of the leather produced increases until the maximum level of pH 4.2 is reached. In practice, the pre-tanning begins at a pH lower than 3 to allow the aldehyde to penetrate through the section. The pH is then gradually raised up to a maximum level of pH 4.0 - 4.2. Higher pH values only intensify any leather yellowing without further increasing the hydrothermal stability.

    The Use Of  Modified Glutaraldehyde

    Glutaraldehyde can be modified by reaction with alcohols. The result is a masked product that is less reactive than non-modified glutaraldehyde. In addition, the modified glutaraldehyde can be blended with a polymer containing carboxyl groups. These groups block the amino groups of collagen, so that the modified aldehyde becomes even less reactive1. This reduced astringency guarantees a more homogeneous penetration though the section, resulting in a finer smoother grain and lighter-coloured wet white. 

    The Length of Pre-tanning

    The time required depends upon the leather thickness. Complete penetration of the pre-tanning agent will be longer for full thickness leathers than for split pelts. In general, for perfect penetration and an optimal tanning effect, leathers must stay in the pre-tanning bath overnight after basification, with the drums set on automatic turn. If the length of the process is shortened, the leathers are of inferior quality.

    Controlling the Basification Process

    In general, basification starts 90 minutes after the addition of glutaraldehyde. The pH is then gradually raised (it is essential to avoid sudden changes) so that the aldehyde can react with the leather slowly and without overloading the grain. If the pH is raised too rapidly this would affect the ease of penetration, would cause coarse grain, and in some cases would even make the leather weak.

    Often the float is first basified using salts that are mildly alkaline, such as sodium formate then followed with very slow additions of sodium bicarbonate. A neutralising auxiliary syntan with a milder action than these traditional basifying agents can be an alternative.

    The Influence of Syntans in the Pre-tanning Process

    Syntans improve wet white sammying and shaving. Their effect is to prevent leathers sticking to the shaving machine cylinder, so that they can be shaved more easily.
    The use of dihydroxydiphenilsulfone-based, light-fast syntans is particularly recommended. In the past small amounts of syntan in pre-tanning were used, which were just enough to guarantee easier pressing and shaving, but now it is normal to use larger amounts.
    The best results are obtained by using 3-5% of syntan. At this level of offer the changes in leather thickness between shaving and the finished leather become more predictable, and there is a lower variation between the thickness of the wet white shaving and the finished leather.

    This means that: 

    · The shaving operation does not compromise the papillary layer
    · The leather doesn't swell in the main tanning phase
    · The wet white leather is firmer, especially in the belly partsthe main tanning phase can be lighter.

    7.4. Pretannage formulation for the production of wet white

    A guideline formulation that takes these parameters into account for the production of a wet white pre-tannage is given as Panel :

    Raw material: green-salted bovine hides
    Splitting thickness : 2,4-2,5 mm
    Percentages referred to split weight

    Rest 12 hours, samm, shave 1.0 - 1.1mm.
    · Ts is approx. 72°C.
    The treatment with bisulfite is useful to eliminate excess glutaraldehyde from the grain, which could reduce elasticity.


    This stage represents the real tanning process, where the shrinkage temperature of the leather is increased from approximately 70°C to 80-82°C. In general, various types of tanning substances are used at the same time including vegetable tannins, syntans, and polymers of different chemical nature. The formulation depends on the kind of article desired. The use of glutaraldehyde in this phase can also bring a number of advantages such as:

    · It allows a reduction in the amount of chemicals that are normally used
    · It improves the penetration of retanning products and fatliquors applied

    As a result leathers will be softer and more constant in production. And, leathers dry better on wet toggling: this is important, as sometimes this stage is not carried out under the best conditions of temperature and humidity.

    8.1. Practical aspects

    The parallel use of vegetable tannins suggests that the process should begin using a short float, low temperature, and with dispersing syntans to assist the penetration. At the completion of this stage-carried out at a slow speed and for sufficient time to guarantee perfect penetration-the float is diluted at a temperature of 40°C, and the vegetable-tanning agents fixed by mild acidification. A stronger acidification is required before the main fatliquor. It is noted that leathers treated as described have a very low isoelectric point. The anionic charge must therefore be reduced to achieve a good fixation of dyestuffs (if necessary for top dying) and of fatliquors.

    8.2. Influence of natural Tannins on the Quality and Mechanical Properties of Leather

    The type of natural vegetable tannin agent used has a great influence in terms of the quality, and on the mechanical/physical properties of the leathers produced. These important differences are given in Panel where, under similar processing conditions, different tanning products have been used.

    Leathers processed with tara showed the best results for softness, surface touch and depth of colour at equal offers of dyestuff. Compared with the other tannins, tara also offers superior values for tensile strength, tear propagation and grain resistance to bursting, elongation at break.  The use of exaggerated quantities of natural tannins causes, in general, a marked reduction of the mechanical-physical properties. This is illustrated in Panel :

    It is important to remember that the use of tara or other natural tannins contributes towards the reduction of any presence of formaldehyde in leathers. The parallel use of retanning and fatliquoring acrylic polymers, with their high capacity to fix to leathers, in combination with sulfited fish oils, enables good fogging performances.

    8.3. Main Tannage: a Guideline Formulation

    A guideline formulation is given as Panel :

    Main Tannage Formulation for Metal-free Bovine Hides:
    Automotive Leather, Shaving thickness: 1.0-1.1 mm


    The term "combination tannage" refers to execution of two or more types of tannages, to give the resultant leather some or all of the characteristics of the individual tannages. Many types of these tannages are applied in the practise. The principal systems are the retannage of vegetable crust leather, semi-chrome leather, semi-alum leather, chrome retan leather. Among them, is particularly interesting the Mimosa-Alluminium tannage.

    9.1. Mimosa-Al Tannages

    The process consists of a low mimosa pretannage , followed by a basic alluminium sulfate retannage, giving a boil-proof leather with a good dyeing, buffing and printing properties. Alluminium ions form complex with the already bound mimosa tannins and so give stable crosslinking. The optimum levels of mimosa extract and alluminium are offers of 15 percent mimosa and 7 percent alluminium sulfate on the limed weight. Systems of vegetable drum tannages have been developed wich give complete penetration of hides with low amounts of mimosa extract (13% on limed weight) in a short period. Retanning this low vegetable pretanned hide with cheap alluminium sulfate gives a boil-proof upper leather , that can be used for determinated types of articles.

    LP.1.3. - Retannage

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:33:56 AM

    The object is: to produce different types of leather from the one semi-finished leather, which is usually 'wet-blue'. The retannage optimises the serviceability of the leather, adapting it to meet fashion requirements and the demands of customers.
    It also creates a dried (crust) leather to allow satisfactory finishing of the dried leather surface.  

    The neutralization, retannage, dyeing and fat-liquoring wet operations are almost always carried out in that order in one operation, with a total time of 3-7 hours. They are done in a drum, or sectioned dyeing vessel, at a range of temperatures between 35-60° C. Drum speed is about 12 rpm. Re-tannage is often understood to include all the four stages.  
    The individual stages of the operation influence each other, so there are adjustments needed to obtain optimum effects for high-quality finished leather. The properties, which can be influenced by the re-tannage include fullness, grain tightness, softness, fat distribution, leather colour, levelness of the dyeing, light-fastness, grain fineness, smoothness, buffing, dry-drumming, embossing, buffing, water repellence and chemical and physical analytical results. It is obviously of great importance in determining the final quality.
    Special treatments, such as water repellency, are an integral part of all leather process design but there will be a part of the retannage, which involves special chemicals. It has to be realised that such leathers have to be designed from the initial wet work to minimise all hydrophilic chemicals.


    The object is to remove strong free acids from the leather by using milder chemicals. This weakens the strong positive surface charge of the chrome leather so that anionic tanning materials, dyestuffs and fat-liquors agents can penetrate and are not restricted to the surface. The leather is said to be 'de-acidified' because it does not usually reach the neutral point of pH 7.  Surface pH is below 5.0 externally and 4.5 internally. If a deep neutralisation is needed to allow other chemicals to penetrate deeper, the external and internal values are about 5.5. It controls the reactivity of wet blue leather and has to produce the same level in all the pieces of leather in one retanning load. It is, therefore, important for treating a selection of wet blue from different suppliers.


    The object is to control and adjust the properties of the resultant crust leather. It is the main use for the synthetic organic tanning materials, but vegetable tannins, polymeric, resin and mineral tanning agents (chrome included) are also used. The environmental concern for trivalent chrome has affected how this material is used. The character of leather is determined by the first tanning operation, but the retannages are an adjustment to that. There are 3 main types of result, depending on the crust required:  

    • Filling of the looser structure of wet blue by vegetable tannins, replacement syntans and resin tanning materials with a selective filling effect. This leather is   also designed to have good tightness, buffing, embossing and finishing properties. This is for corrected grain leather, which is the lowest quality of the wet blue selection. 
    • The full grain selection has a good grain and cutting value. The retannage is designed to have less filling to retain that natural elegance with a good break, full colour shades from dyeing and an attractive feel from a full handle over all the hide or skin. Softness and an attractive look are often more important than the tightness of the lower grades. The eye appeal is the main sales factor in top quality leather. 
    • A compromise of the others, so that there can be further sorting in the crust to optimise quality, value and profit for the tannery. It is a valuable option to have a versatile retannage, suitable for finishing as either full grain or corrected grain.


    The object is to colour the leather as required by the customer, or sales forecasts. This should be an even colour and should cover any grain defects. If the leather will not have a covering finish, the colour should be light fast, and wash fast. It is usually done in drums, or sectioned dyeing vessels, with different levels of float and temperatures. Not all leathers are drum dyed. This may be done to leave more choice in deciding the product to make from the crust and to save the cost. Dry crust leather can be dyed by through feed continuous methods. At present, this does not produce the same qualities as the batch dyeing due to the limitations of time, temperature and dyestuff type. There are many controls to affect the results and there is a wide choice of dyestuffs, which are high cost materials. These are often in liquid form for easier, and healthier, handling. Health concerns have also banned the use of dyes containing known carcinogenic chemicals, and these are not produced by any reputable company.
    Dyeing can be with anionic and cationic types but the whole retannage process needs to be designed according to the dyeing conditions. Colour matching is an old established human art, being replaced by instrumental colour measurement in larger tanneries.
    Wet white leathers are often required to be dyed with dyes free of heavy metals, to meet the ecological requirements.


    The object is to soften the leather, as required in the product, by lubricating the wet fibres, with a fatty emulsion, so that they do not stick together on drying. Without fat-liquors, the leather would dry hard and any mechanical action would damage the fibre and limit the quality potential. It controls the feel of the dry leather. It is normally the last operation in retannage and can be combined into that float. These emulsions of materials have different stabilities and care has to be taken that there is the required degree of penetration and fixation. Complete penetration produces leather with a cloth-like feel, suitable for garments, compared with a surface effect, which would feel greasy and be difficult to apply a top finish. Care and experience are needed to select the correct balance of materials. The method of drying also needs to be considered when deciding on the fat-liquors.
    Fat-liquors, with suitable stability, are also applied during tannage to obtain a deeper coating of the fibres.  

    After the final wet operations (retannage etc.), the leather is generally horsed up or stacked on platforms overnight. The water content is about 70-75%, on the leather weight.


    The object is to reduce the water content and to spread the leather out by stretching it in all directions. The helical blades spread the hide, or skin, into a flat shape and squeeze out the surplus water. Animal skin is three dimensional to cover the animal shape, so this operation now starts to change that into two dimensions. The shapes need to be positioned on the rollers to avoid any creases forming in the surface; this can be difficult for the shanks. After setting out, the leather should be easier to handle for subsequent drying.


    The object is to eventually take the moisture level down to about 8-14 % for mechanical softening. Water evaporates from the surface in two stages:  

    • The first stage is at constant rate with the surface completely wet so that the water can migrate to the surface from the centre of the hide at the same speed that it evaporates. This is unbound water and the heat of the drying does not affect the leather temperature because of the evaporation effect.
    • The second stage, the falling rate stage, is when the surface is only partially wet and the temperature of the leather itself will start to rise. This is a critical stage and can damage the leather if moisture is trapped in the centre.

    Uncontrolled drying is not advisable. Shrinkage of the leather also occurs during drying and is a factor in costing. Higher temperatures create higher shrinkage. However, this shrinkage should not be physically restricted because the leather would become hard and unacceptable, with the fibres unable to reposition themselves at different moisture levels. Slow drying, at a low temperature, produces the softest leather with the lowest shrinkage, but this is not normally economical.
    It is not normally possible to dry the leather to its required physical condition in a single operation. First there is an initial drying and there are 4 main methods used:  

    • Suspension, or hang, drying where the leather is simply hung up in the drying room or tunnel, with controlled conditions of temperature, relative humidity and air circulation. The resultant dry leather feels full and round with good softness, but has the serious disadvantage that area and smoothness is lost. All such leathers must be toggled after staking to recover sales value and profit.
    • Paste drying has the set out leathers pasted onto cool glass, or non-corrosive metal, plates with an aqueous adhesive solution and then passed through a tunnel drier for 5-8 hours. These machines generally have a total of 100 to 200 of these vertical plates and up to 50 metres long. The leather passes through a number of sections, each of which have well controlled drying conditions enabling the drying rates to be progressively matched to the different stages described above. This resultant leather needs some softening, but it is flat and has a better area yield than suspension drying. The residual paste film means that full grain finishing is not normally possible, but it is ideal for such buffed leathers as corrected grain or splits. There also exists the possibility of special pastes, which can be removed easily for full grain.
    • Vacuum drying is the best method for most full grain leathers, whilst it is also perfectly satisfactory for corrected types. The set out leathers are laid flat, grain down, onto a stainless steel table, where they are also stretched out further by hand slickers as their shape dictates. The table top and flattened leathers are then enveloped by a sealing hood. Reduced air pressure then allows drying to take place at a lower temperature, with the hide, or skin, being kept flat in position by applied pressure, reducing shrinkage. The temperature is about 75°C, and even less. After a few minutes, the leather is removed with the grain side dry and the flesh side slightly damp. It must not be dried out completely to the lower limit, but hung, without tension, in the ambient temperature to lose the final moisture freely. These driers have been developed into multi-table machines and the most sophisticated systems have a conveyor delivery from the setting out through vacuum driers, to staking and toggling operations. These have great potential for large productions. Process time and labour content is significantly reduced.
    • Toggle drying stretches the leather manually onto perforated metal sheets, so that the shape is retained and flattened by the toggle clips, which have pincer grips. These hold the edge of the leather and are fixed into the perforations of the sheets by a small positioning foot, or lug. The drying conditions and control are as for hang drying. The frames are sometimes assembled as a type of bookcase or, much better, as a form of conveyor, which has greatly improved this whole operation and reduced the handling. Toggling is used for upholstery, side clothing, splits and lining leathers. It has 10% more area than hang drying but at the expense of quality, because of the tension produced from the toggles. Stretching prevents some shrinkage. It is better for vegetable tanned light leathers, which shrink less, and for re-toggling damp leathers after mechanical softening and dry milling. Here it keeps the leather soft and flatter.  

    These initial drying methods produce leathers, which are too hard and have an uneven moisture content, but below the normal 14%. They could not be finished in this state.

    LP.1.4. - Crust

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:34:24 AM

    The dried leathers have a series of mechanical operations for softness and general presentation so that they can be sorted for final top finishing, or for export.


    The object is to give the leather a moisture content of 18-22% to allow mechanical softening. The dried leathers have different levels of moisture from drying at 8-14% because of the different thickness and conditions. In practice, leathers are dried to the lowest level at the first drying, so that subsequent conditioning can produce uniform moisture content and allow a uniform softening. Conditioning adds a controlled amount of water to the leather, usually on the flesh side. This is normally a simple spray application combined into a string conveyor, and a great improvement over the use of damp sawdust. The moistened leathers are piled flat and stand for 24 hours to allow the moisture to reach equilibrium. They should be covered with plastic sheets during this time to maintain the required microclimate.


    The object is to mechanically stretch the leather, separating the fibres, which have become attached to each other during drying. It is important that the moisture content is correct, in the 18-22% range. This is often recognised by touch and handle better than a moisture meter. If the leather has too much moisture, there is insufficient movement of the fibres and the resultant leather is not soft enough after drying out; if the leather is too dry, less than 18-22%, the fibres are damaged by the mechanical action. The actual extent of the fibres self-attachment varies with the wet processing, particularly fat-liquoring, and the drying conditions. The conveyor driven vibrating staking machine is excellent for most leathers, and causes less damage than earlier types. It also has an advantage that the operators need less training. The older jaw-type staking, Slocomb, machine is still suitable for special softness provided there are skilled operators; it has a poor safety record because the manual operations do not allow adequate guards to be fitted on all the moving parts.


    This option of a fast revolving (20 rpm) dry drum is increasingly used to produce very soft leathers with a relaxed surface appearance. It could be for upholstery, garments, or casual shoes. There are degrees of development, with dust extraction needed to clean any fibres from the atmosphere. It can be done on crust leather without finish, split, suede or on finished leather, provided the finish film will withstand the mechanical action. Several hours running are needed; the internal surface of the drum must be smooth to avoid any damage to the leather surface. The leather needs to have the toggling afterwards to restore the flat surface and the area.


    The object is to dry out the softened leather in a flat state, from the conditioned levels of 18-22% to the normal dry leather, which contains 14%. This level of 14% is the norm for all natural fibres and the leather should not feel damp at all. It can be stored in this condition, which is not the case for the conditioned leathers, which become harder and can develop mould. Toggle drying, or paste drying, is used and the times are short for this mild drying. The temperature used can be critical to prevent area loss. Yield is always better at as low a temperature as possible, for example 18°C is better than 30°C. It is feasible with a low amount of moisture to remove and reasonable air circulation.

    TRIM - with by product of dry tanned leather waste

    After the second drying, the leather will be flat but there may be folds, pleats or ragged edges in some areas, which either disfigure the appearance or will prevent further operations being done correctly and without damage. For example, the leather would not be able to pass between some revolving cylinders in an even manner. As always, it is important to control and supervise carefully trimming operations, because it is all too easy to trim away too much leather, lose the sales value for the piece and profit for the tannery.

    CRUST SORT - (with an option to export)

    This is the second quality control point, after the wet blue sorting control. It is an important stage and sorters need to have good experience and judgement, because so much of the grading is subjective. The standards have to be consistent.
    The surface is assessed for potential cutting area and the extent to which defects and damages reduce that area and quality value. The break of the leather is also checked together with the actual thickness (in tenths of millimetres) and how the leather feels on handling. There will often be different dyeings, which have to be checked for shade correctness in finishing.
    A finishing load, or batch, starts here and is now going to be specifically for a certain type and colour of finished leather, and usually for a specific customer. The best qualities are for full grain and have different degrees of covering finish to improve their cutting value. The worst grades need to have a corrected finish, where the grain is removed by buffing.
    The crust stock is an important logistic asset because it can be the means of making quick deliveries to customers, provided that there is the suitable crust leather available. This means the suitable grades, thickness, base dye colour and character to meet the requirements. Finishing can be the means to adjust the surface appearance.
    The export option also involves having leathers with the required properties ('the quality') and quantity required by the buyer. Selling in this way is only possible in established trade based on full confidence of sorting standards.

    LP.1.5. - Finishing

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:34:58 AM

    The object of finishing leather is to improve its serviceability by protecting it from damage by water, soil and mechanical action. At the same time, it is also improving the cutting area. Finishing adds value by improving the surface appearance so much that the leather becomes attractive to look at and attractive to touch and feel; any of the surface defects below the finish cannot be seen or considered by the buyer, or the ultimate user of the leather product. Experience and an appreciation of colour effects are needed to achieve the desired results. The technician often has to be able to develop a finished look to match a competitive sample in a short time.  
    Finishing can modify the shade, gloss and handle of the leather, improve its physical properties (such as its light and rub fastness), and hide any defects or irregular appearance. It is heavily applied to corrected grain leathers and to splits in order to imitate full grain leathers and often used to obtain fashion effects on all leathers.
    The lowest grades of leather need the most finishing work, compared with the minimum amount of finishing for the best grades. At the same time, the best grades sell at the highest price and the lowest grades at the lowest price. With such a difference in the finishing costs for these extremes of sales prices, it can be seen that the top quality traditionally has a much higher profit margin than the bottom quality. It is naturally essential that all grades and qualities are eventually sold, although it will be to different buyers.
    Aniline leather is considered the top quality because the transparent finish does not cover any of the surface full grain. Originally, it referred to leather without any finish, which had been drum dyed with aniline dyestuffs and this was the only colouring it received. It should now mean that there are no covering pigments used in the finishing films; therefore, the leather has to be almost without defects. Most finishes for a classic appearance on leather do have some covering property, but try to produce the aniline effect by incorporating dyestuffs at some stage.
    The shortage of high quality raw material means that a lot of progress has been made to upgrade the lower grades, by improving the cutting value and surface appearance. The section on upgrading shows some possibilities.   

    All the individual operations are options according to the finished article and the quality of the crust to be finished. Normally, there are several layers of finish applied and the constitution varies between the different coats - base coats, top coats and pigmented coats. Adhesion to the leather and inter-coat adhesion is essential in wet and dry conditions. The flexibility of films has to match the flexibility of the leather. For example, there is difference in leather for garment, glove, shoe or upholstery. The lower films in a finish are more flexible with good adhesion to the base, compared with the upper films, which provide the protective surface by being harder. The top coat needs to be the most resistant to damage. The film properties are built up progressively in the finish, with different formulations for base, intermediate and top coats.  

    The table gives a general scheme for better full grain grades with more pigment being used to cover problem areas, assisted by some printing (embossing) with hair-cell to give an even grain appearance. Corrected leathers have more finish coats and need attention to impregnate and seal the buffed surface.





















    Aniline Effect







    Spray to cover

    Aniline Effect



    There is a large variety of finish formulations, which are mainly water based. There are different colouring materials, including inorganic and organic pigments, dyestuffs and waxes, feel modifiers, matting agents, fillers, polymers of all types, casein, dispersing agents, plasticizers, diluents. These are applied to the leather in several coats; starting with higher rates such as 20 grams per square foot, and ending lighter as 5 grams.  

    Care has to be taken in handling the leather so that the surface is kept as flat as possible during all the finish operations. Creases and folds reduce the finish effect and certainly lose value in the finished leather.

    APPLICATION always involves waste finishes as liquid or spray

    Hand padding and spraying have been almost replaced by roller and curtain coaters and spraying machines in all medium and large productions. There are exceptions for special leathers, developments and samples. The costs of finishing small batches are high if the large amount of finish needed to prime the machines has to be eventually discarded. Controls on spraying machines reduce waste and are important to reduce and control toxic emissions from spray exhausts. This prevents atmospheric pollution from Volatile Organic compounds (VOC). Conveyor drying and stacking machines are linked into the finishing lines.


    The object is to improve the value of the lower quality raw material, including splits. It includes the following possibilities:  

    • A complete film, with embossing or grain pattern, transferred from a previously coated release papers. Ideal for splits and gives high abrasion resistance with a good appearance. They can be used from shoes to leather goods and smaller parts of car upholstery.
    • Laminated film, glued to splits. Used for sport shoes and a wide range of fashion effects. A major use is for leather goods and belts. 
    • High coverage finishes. A thin film with reduced transparency gives a natural appearance and can be used on full grain without the risk of overloading a sensitive grain.
    • Stucco fillers. These are a type of plaster and are applied by hand, or roller coater after impregnation and re-buffing. The surface becomes more even as the small scars and scratches are physically filled. After application, leather is re-buffed and finished conventionally. Needs care to avoid poor lasting and low flex resistance.
    • Cationic products can give good base sealing because they are the opposite charge to the subsequent normal anionic finishes. It prevents absorption and seals defects.
    • Foam finishing. The foam is produced in a finishing mixture by a special pump and applied from roller coaters. As the foam does not penetrate deeply, it maintains the softness of the leather. The trapped air results in a thicker film, compared with a film of equivalent solids content from a roller coater. Consequently, it covers well and has a natural appearance. It also embosses well with good print retention and flexibility. The most common use is on splits and heavily buffed leathers.
    • Fine buffing, polishing, the use of sandblast and hair cell grain embossing plates below the finish, all are disguising the basic problem areas.
    • Roller coaters are an important finishing machine, with an increasing variety of uses as both the mechanical performance and the finish formulations are developed in different directions. The leather has to be flat, and firm enough to pass through the rollers without damage. Concentrated finishes can be applied cleanly to low quality leathers. Like curtain coaters, the viscosity needs to be regulated and polymer emulsions need to be mechanically stable.
    • Reverse roller coating is especially good for white leathers because fewer coats are needed and it is easier to keep the leather clean. Finishing white leather otherwise is a difficult operation.
    • Synchro-roller coating, also known as direct forward coating, is for soft full grain side or on sheep nappa. It applies a thick soft film, which does not firm the leather but does cover defects and seal damaged grain.
    • Gravure printing by engraved rollers and the surface tipping of embossed or milled leather produces unique surface designs and disguises defects.
    • Fashion effects such as rub off, oily pull up, semi-aniline (transparent coloured films on a covering base film) and other optical effects are all used to distract the eye from the defective area.
    • Dry milling breaks up the surface appearance and hides the defects underneath.
    • Finishes with special properties command a special price, and needs a specific approach. The special property becomes more critical than some natural defects. Such leathers would include scuff resistant, water repellent, washable and dry cleanable finishes.

    BUFFING and the production of waste as dry tanned dust

    The object is to obtain a more even surface for finishing on low quality leather, where the grain has defects, which cannot be covered uniformly. The grain surface is buffed off by a fast revolving cylinder, covered with abrasive paper. This reveals an even surface with a suitable base for heavier finishing coats. Buffing papers are graded by the size of the grit, so that 80-100 are very rough, and would only be used for the start of producing a suede nap appearance. 150-220 grits are finer and suitable to start buffing a corrected grain leather. Finer papers are 280,320 and 360. A buffing sequence is normally at least 2 different grades on the grain- say 220 and 320. Buffing too deep gives too much absorbency and penetration of the finish, which makes the grain open and the surface unable to be filled by the finish. The final buffed surface has to have even absorption, so it is often necessary to buff the thinner belly areas with a separate cut, with a small width machine or feeding in a different direction towards it. Normal buffing is done from butt to shoulder, but it is also done in both directions. The flesh side of full and corrected grain is often buffed as required.
    Buffing cylinders revolve at about 1000 rpm and the machines have to be connected to efficient dust extraction systems.
    The type of retannage affects the buffing properties, in that there has to be surface filling of the grain to allow the degree of buffing. Vegetable or replacement syntans are preferred.

    DUST REMOVAL - with the collection of the dust for disposal

    After each buffing operation, the leather passes on the conveyor of an air-blast de-dusting machine underneath a thin jet of compressed air, which clears the dust by blowing it into the attached extraction system. It is important that the surface is absolutely clean, and free of dust, for proper finishing and appearance.


    This operation is an option and has the object to reduce the looseness of the leather structure by making it tighter and firmer, and to improve the selection. It is used on leather, which will not be suitable as full grain, and has been buffed. This buffing needs to be done so that the whole surface has an even absorption. If leather is given a relatively heavy finish coat, the appearance is often unsatisfactory because it does not look natural and has a poor break. To avoid this, corrected grain leathers are sometimes impregnated with penetrating dispersions. These must penetrate deeply and stick the looser layers of the structure together. About 20-30 grams of mixture are applied per square foot, which has to be done by curtain coater, roller machine or airless spray. After standing overnight to allow maximum penetration, the leather is dried flat, preferably on a lower temperature vacuum machine. The surface is then either polished, if it is full grain, or rebuffed, if corrected, with a fine 400-grit paper and de-dusted. The result is a smooth sealed surface ready for further finishing.


    Spray staining with liquid dye solutions is done to colour the surface of un-dyed leather and to level drum dyed shades. It is used for all grades of leather.


    This is done with a fast revolving cylinder made of stone, felt or resin roller and used on all types of hides and skins. It flattens the grain and softens the leather, with applications before, and between finishing coats.


    This is the first and the most important coat of finish because it has to provide the adhesion of the whole film to the actual leather. The composition is formulated to meet this priority. The polymers used are soft and flexible. The formulation will usually include some covering pigments and fillers, to hide as many defects as possible.


    This is considered to be a main covering coat due to its pigment proportion at 100-150 grams per litre. It can be applied by pad, roller or spray. Later coats have reduced pigment levels to improve the natural appearance. Organic pigments are more natural than inorganic and can be used at 25 grams per litre, without affecting the transparent look. It should always look as natural as possible.


    This transparent coloured coat contains dyestuffs, which is slightly darker than, and contrasts with the colour of, the covering base coat. The effect of this colour contrast is to appear as an aniline finish, with the clear dyed film disguising the pigmented look below it.


    The final coat has to protect the coloured film below and is important for the fastness properties of the film. It determines the final look and handle of the finish. Traditionally, it may be in solvent or low-solvent solution. Special cross-linking systems to cross-link acrylics and urethane films are now used to achieve the same properties without solvent emission being a problem.


    Pressing and ironing are intermediate and final operations in building up the finish film. The straight through heated rollers are preferable for productivity and maintaining leather softness. The hydraulic ram presses use heavier pressure to compress the fibre structure, and are essential for obtaining an effective embossing print.


    Classic glazed kid is made by the original design machine with a glazing jack, usually of glass, which rubs the leather surface with a reciprocating action. The heat and pressure produced give a deep glaze effect, due to the protein binders and dyes, and gives a true aniline appearance. The machine principle is unchanged for many years and needs skilled operators. Although, there are safety concerns in the handling of the leathers, it does produce a unique appearance. The wet fastness is a problem. A rotary ironing machine gives the nearest alternative effect, and does not need the same amount of skill for operation. It is also used for hides.

    DRY DRUM (MILL) AND TOGGLE - some dust produced from drum

    This option of a fast revolving (20 rpm) dry drum is increasingly used to produce very soft leather with a relaxed surface appearance. It could be for upholstery, garments, or casual shoes. There are degrees of development, with dust extraction needed to clean any fibres from the atmosphere, and a moisturising spray injection. It can be done on crust leather without finish, split, suede or on finished leather, provided the finish film will withstand the mechanical action. Several hours running of the drum is often needed. The leather has to be toggled afterwards to restore the flat surface and the area.

    FINAL SORT , and often trimming with production of dried waste finished leather pieces and trimming

    Here is the final quality check and assessment of the leather value, sorting into different grades. There is a limited amount of light trimming, where this improves the selection and allows an upgrade. This is another skilled operation and determines the financial balance of each production lot and the impression it makes on the customer. Any leather, which does not meet the standard required, has to be dealt with separately; in a different grade, reworked or rejected.


    The area of the sorted leathers is measured, usually electronically on a horizontal conveyor. The accuracy of the machine needs to be checked on a daily basis with a template. The individual area of each piece can be stamped on it, together with a suitable code to identify the production lot and permit it to be traced.


    It is important to maintain the finished appearance in packing so that the leather can arrive in the customer's warehouse looking as attractive as it did when it was sorted in the tannery. It can be difficult to achieve this when there is a lot of handling in shipment. This normally means that some finished leather, sensitive to damage, is rolled with the grain surface on outside of the roll; others are placed grain to grain. Smaller skins are folded. The outermost piece is covered with a protective wrapper, which is then fixed tightly with a non-damaging tape or chord. It is important that the leathers are held tight to prevent any possible movement in travel. If feasible, small leathers are packed flat onto small pallets. It is important that any packing for individual rolls is permeable to avoid moisture being trapped during the time of shipment. Cartons provide the best protection against the handling in transit, with several rolls or bundles in each carton. A container shipment with cartons of leather packed by the tannery is ideal. It is essential that there should be no risk of damage from the weather. Wet, cold and heat all affect finishes and leathers.


    The documents for shipment need to show all information to conform to the original order and the production schedule of the tannery, to allow tracing and form the basis of future orders. These details also allow the tannery to check the financial contribution made by this production lot.

    LP.1.6. - Production chain

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:35:24 AM

    The industry process chain may be split into 6 main production stages and the product at each stage has the potential to be traded internationally. The relative increase in added value and potential commercial profit can be seen as the raw material passes through the various stages of the chain.

    1.  Raw material: The raw material comes from cattle hides, and from the skins of other animals.   It is biodegradable and loses structure and value if it is not preserved correctly and promptly after slaughter. This is normally by salting or drying. The hides and skins need to be without decay, cuts or damage, and of good shape.
    In contrast to the well-developed quality and market standards in developed countries, this is critical factor in developing countries, which persist in primitive systems encouraging informal trade and preventing the full potential value being obtained.
    A proposed African scheme is well designed but not implemented yet. ESALIA/CFC sorting standards classify ground, ball and smoked dried hides and skins as rejects; the lowest of 4 acceptable skin selections has defects up to 40% of skin area; above this 40% means that the skins are total rejects, together with untrimmed or poorly trimmed skins.  Hides also have 4 grades, with the lowest grade having defects up to 50% of the hide area; above this 50% is a total rejects.  'Fallen' hides and skins originate from animals dying naturally and are considered as reject material, unsuitable for processing. After soaking and hair removal in alkaline liming, they are pickled.            

    2.  Pickle: The pickled state is a wet, acidic condition and a preparation for tanning the leather. 'Pickled' leather is a traditional product, a commodity for export shipment of skins, which allows the importing tanner the widest choice in tanning materials. All other semi-processed materials have already been tanned and offer less flexibility regarding their potential final product.            

    3.  Wet blue: Wet blue, and Wet White, comes from the tanned state. Tanning gives permanence to the protein and stops further decay. The 'blue' refers to the more general chromium tannage, compared with the newer chrome-free white tannage. (Vegetable tannage is an older process, and still used for some upholstery, belts and sole leather. The natural colour of vegetable tannage is brown. It is not traded in the wet condition.)
    'Wet blue' leather is well-established as a commodity for international trading, because of the widespread use of chrome tanning.  As such it is price sensitive, provided quality and reliability is established.  As stated above, this form of export is increasingly preferred by importers, because it arrives without risk of transmittable diseases, a factor of concern with unprocessed hides and skins.  It also has the advantage that all processes, which cause the most damage to the environment, have already been carried out in the exporting country. A further advantage is that importers can specify the range of the quality selection they need to buy - which conversely means that the exporter has to consider the sale of the other grades.
    'Wet white' leather is of increasing interest where chromium is to be avoided - for example, for automotive upholstery. These FOC ('free of chrome') leathers are expected to experience increasing demand in the future, as environmental concern and legislation grows.
    After tanning, the wet hides and skins are usually dyed and further treated with softening chemicals. After drying, their condition is known as the 'crust'.  This is the first point in the process at which they are actually dry.        

    4. Crust: Crust leather is dry and is easier to ship. It is also easier to see the quality of the surface appearance for grading and value judgements. It is ready for further processing, either for more wet  work (retanning and dyeing), or for direct dry finishing.
    It may be pure vegetable tanned crust, or a combination of chrome, synthetic and vegetable tannage. It is an advantage to develop such a product for a specific customer, who provides the guidance; otherwise it is much more difficult.
    Properties such as tightness, softness and the response to finishing operations are critical in making a good product and demand greater technical ability.
    Although some countries propose that exports should only be allowed as crust, or at an even later stage (in order to add value), the results have often been negative. The hides and skins from individual animals are different, and unique in their appearance, reflecting the animal's history. The classification of relative quality is the key operation in a tannery, and is carried out at several stages in the process.
    The profitability of the whole business depends on using the grades for the appropriate products, and making an overall profit from all the raw material used. There should be no inventory without a potential sale ('dead stock').
    After sorting for quality - surface appearance, feel, thickness - finishing coats of colour are applied, to improve the appearance and serviceability of the hides. These qualities are all customer-specific.           

    5.  Finished leather: Finished leather has the potential to add even more value and to provide much better earnings, but it also is much more difficult to achieve successfully. Compared with wet blue leather, which can be made into a number of final products, finished leather has to be made in a specific type, colour and thickness for each specific product (and usually for each specific customer). There is no room for error to achieve a profit, and it is essential to develop finished leathers for each grade of crust material.  The necessary semi-processed hides and skins (stages 2 to 4) are taken from the normal production line, according to the demands of the market.  Specialist processing equipment is involved through all the stages.           

    6. Finished leather products: Finished leather products are made from the different leathers into a wide range of products. The major use of cattle hides is for the uppers of heavier leather shoes, but there are increasing demands for furniture and automotive upholstery. Skins are used for lighter shoes, leather clothing and gloves. Large and small leather goods, from suitcases and golf bags, to wallets and briefcases, are made from both hides and skins. Each finished leather product has its own specific leather requirements.


    Note:Please note that all costs and financial calculations are shown as guidelines and as such they will need to be confirmed with the local conditions.

    LT.1.1. - Marketing

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:36:04 AM


    Originally, overseas sales started as business expanded from an established and successful domestic business. For example, established shoe shops selling locally made shoes would be a good base. The products could be assessed for competitiveness on the export market, and developed accordingly.  

    In the modern economy, a local shoe production is often impossible; it cannot survive financially due to the intense competition and changes in the buyer-driven production chain of the current global market. A country has to have a comparative advantage over others for a secure position in that chain and   potential exporters need to know if they also have a comparative advantage to allow them to be internationally competitive and successful. An example is China, which has the advantage of a huge population of potential workers and low labour costs. They also have the advantage of an extraordinarily open economy, with an international trade in goods and services being 75% of GDP. This compares with 25-30% for other economies such as EU15, US, Japan, India and Brazil. However, it does not have a large enough livestock resource to make sufficient leather for its production of leather products. It has only a limited area of land available for agriculture to feed the huge population, and there are serious concerns of environmental protection for the future. Also, in the future, wage costs will rise because the work force will become smaller as the 'one child family' matures.  

    Many developing countries would share some of the characteristics, from the low cost workers to the environmental concerns. They may have a relatively more abundant national resource of livestock, which has potential for more added value and trade, and they may have a more abundant work force.  

    In considering strategy, there are three main factors, which influence the potential for developing a local leather sector:  

    • The local meat industry. It is important to realise that the potential value of the by-product of hides and skins depends on the actual state of development of the national meat industry. The animal husbandry, which is good for meat production, gives healthier animals and better quality hides. Careful slaughter and preservation reflect better-managed facilities and give better value hides.
    • The availability of the local water resource. It is estimated that by 2025 two out of every three people in the world will live in water-stressed areas - where water consumption exceeds 10% of renewable water resources. Leather production needs considerable quantities of water and should not conflict with the national priorities of human and agricultural demands.
    • The need to protect the environment from the effects of industrial pollution. Developing countries are aware of the concerns and the need for all industries to be sustainable and non-damaging. This is becoming established globally, together with the legislation to enforce treatment of polluting waste. For tanneries, the waste water (effluent) from pre-tannage and the waste chrome tanning liquids contain the most polluting chemicals and have an increased biological oxygen demand. Ecological concerns affect almost every chemical used in leather production. Such properties need treatment before the waters are discharged into the local environment, which is often important farm land. The costs of effluent treatment are estimated at 5-10 % of production costs. The overall costs have to be kept within acceptable economic parameters.          

    Market analysis shows the extent of trade and of the different product types involved. The exporter has to decide which stage it is possible to trade in, and which product in the buyer-driven value chain can be produced, within the current available production facilities and capacity. There needs to be a viable profit margin. The available raw material is a major factor in the type of potential product. It is essential that a personal assessment is made of the competition and the opportunities in a market. After product selection, a target market (of customers) is selected, so that there is a limited start in the global market, with one step at a time. The strategy should allow for expanding the business by increasing present production or by extending further along the chain. This may mean that collaboration is made with larger, and better equipped, tanneries or shoe factories. There are economies of scale in large units, which should be considered. This production strategy may mean out-sourcing, a joint venture or direct sale to customers. Co-operation between neighbouring countries can be envisaged for joint processing. Comparative advantage is the key to being competitive.  

    Raw hides, and wet blue, can be stored for long periods provided the storage conditions are good for preservation. A cool temperature and a good covering are needed to avoid any drying out of the semi-processed wet hides and skins.  

    As the final sale price is quite volatile, it is advisable not to hold large quantities in the higher processed value, and to avoid the risk of unexpected market changes. Ideally, there should not be large stock levels, which are a handicap in negotiating prices.


    All customers need to have confidence in the supplier that the product quality will be consistent and uniform. They need to be confident that the supplier is in control of all aspects and is reliable for quality and for delivery. It is always important, but especially so for exports from an industry in a developing country, where a good reputation has to be earned and maintained.  

    As explained in the overview, the natural resource of lower grade hides is having an increased demand as the market looks for the lower price raw materials. The trend is also towards a semi-processed state (usually as 'wet blue'), which adds value but it also needs more experience and expertise to produce.  

    The facts to be checked are:  

    1. What are the needs of current and potential customers?
    2. What type of leather is being traded internationally, based on a similar raw material to the local supply? 
    3. Does the local tannery produce this type of leather?
    4. If so, how does the local standard relate to the international products?
    5. If it is inferior, does the tannery have the technical capacity to improve?
    6. Is the raw material quality good enough? If it is sub-standard, there may be limits to extending the trading.
    7. Is the quality grading to the international standards?
    8. Do the production facilities have all the facilities (personnel, equipment and technology) to process the available raw material to the export standard? The quality and quantity need to be built up progressively.
    9. Will the supply be able to meet the market demands of quality, quantity and delivery time? All are needed to become a reputable supplier. A good reputation takes time to establish, and is soon lost by poor performance.
    10. Logistics are most important for international customers, who have a wide choice of possible suppliers and delivery routes.


    The leather sector process chain adds value at each stage, and there are possibilities to trade at the different stages described above (provided there is a customer demand). The priority is to supply what the customer demands at a competitive price that allows a viable profit margin. The sector overview has described trading developments, with the chain becoming buyer-driven and productions transferred internationally to countries with the greatest comparative advantage to reduce costs.  

    Costs and quality are the important factors. The focus on costs requires all potential exporters to have accurate costings and cost control to ensure their trading is profitable. Quality control is associated with technical competence, which is also essential for the product development needed for successful marketing. The whole profitability depends on using all the grades for the appropriate products, and making an overall profit from all of the raw material used.  

    Semi-processed leather (wet blue, crust) should be without the 'reject' qualities, described for raw material. It will have grades closer to the final cutting values. As all the grades have to be sold, the prices have to be in proportion to that value of the grade.              

    Marketing a processed natural product means that there will be a variety of qualities corresponding to the natural variety of the raw material. An original purchased quantity of hides, or skins, cannot all be converted into one particular type of leather, because the quality range is too wide. The collaboration between sales staff, with their marketing analysis, and the technical production staff, has to result in leather which maximises the profit, and sales appeal, for all those original grades. Basically, this could cover a range of products from full grain leather to a corrected grain, or embossed appearance. Sorting pieces of leather into quality grades (selections) is the basis for sales value because they correspond to the comparative cutting values for the final products. That value is a measure of the leather area suitable for the respective leather product. It could vary between 60% and 95%, for example, between the lowest and the highest grades.  

    A production batch of leather will always have a variety of grades and it is necessary to sell all of them. This is the reason for the different prices for each grade. It would be unusual for one particular customer to take the whole range of original raw material qualities and so an alternative product has to be produced for sale, from these other qualities. They can be the means of bargaining and pressure to reduce the overall prices; consequently consistent and transparent sorting grades have to be established. The marketing operation is not complete until all the variety of the original grades has been sold; some grades are always more difficult to sell than others, and so are often sold below cost. (See costing and pricing.)  

    It is an advantage if a producer can have an individual brand name, so that customers associate the name with good performance and good value and it becomes a preferred brand. It may allow for an increased profit margin on the sale. This is particularly the case for special leathers, such as a water resistant type. This is the value of a 'niche' product.  

    Customer service is an essential part of the sales co-ordination role between the tannery production team and the end user. This after-sale activity ensures that the product delivered is acceptable and provides the base for a repeat order, which is the formula for a successful business.  

    Finished leather quality needs close liaison between supplier and customer. The Quality Control system is an integral part of service, checking the standards of production for physical and chemical specification, as well as ensuring that a particular colour in each delivery of finished leather is identical to previous deliveries of the same colour.  

    The distribution system for leather is now world wide with the raw material from one country processed into leather in a second country, and then made into the leather product in a third country. The logistics are usually trans-continental. Coordination may be done by individual companies, who are not themselves involved in any stage of production. They out-source the manufacture to reduce costs (and to optimise their own profit) and to meet the demand of the final retailers. Ultimately, the retailer is the deciding factor if the whole chain is successful. Their requirements are known to the chain of producers, who have to meet the sample patterns provided in all respects at the different stages.

    LT.1.2. - Quality

    Managing quality
    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:37:42 AM

    The dictionary definition of quality in any product is that it is the characteristic property of that product, and a measure of its standard of excellence of the product.            

    Quality in a finished leather, or leather product, means an attractive appearance, a long lasting material and a high standard of workmanship. It is related to price and a good quality relates to a higher price compared with a lower standard of quality. The assessment of value, for a certain quality at a certain price, depends on the customer. However, often they are not aware of differences in leather quality.  

    Leather production starts with a material, which is already below the top quality standard in surface appearance, in different degrees. All of the variables should be related to the raw material price. Processing aims to improve the appearance, and so add value. This will involve more costs for the lower grades, compared with the lower costs for the top quality raw material, because much more work is needed to produce an acceptable appearance. For example, the top quality aniline leather has the thin, transparent coloured finish film. Lower qualities need to have covering pigment films, which cover and disguise defects, before they can have an approximately similar aniline appearance. The focus on upgrading the lower priced material has been most successful in the supply of lower priced footwear and leather goods. Of course, it still does not really look like the top quality, but the lower price compensates for this and makes it attractive to the customer from the value aspect. The customer market has to be selected for the particular raw material and production potential available from the facilities. 


    Leather needs to have a consistent appearance, with a consistent chemical and physical composition. It also has to behave consistently in the manufacture of the product, for example in the lasting and shaping of a shoe. Customers need to have confidence that the tannery is in control and will be a reliable supplier for quality and delivery. It is always important, but especially for exports from an industry in a developing country, where a good reputation has to be earned and maintained.                        

    To manage quality, control of the relevant property is needed to make this reliable product from a variable raw material. Many of the characteristics of leather are subjective (appearance, feel and softness) but some are objective (thickness and colour). A quality standard does not truly refer to perfection but to an agreed balance between the customer's need and the supplier's capability, which may be described in the sales contract and may incorporate a sample pattern for colour, feel or type of appearance. It is also involves mutual understanding and agreement. For raw hides and skins, the standard may be the proportion of different grades of sound material, with grades based on the potential final value of the leather produced. The customer needs to have the consistency and reliability of a uniform supply, within an agreed tolerance.  

    Once the different standards are established, plans are made to control these at different process stages, by checks and inspections. It is known that process conditions need to be consistent to achieve reliability. Consequently, recording systems are needed, depending on the product required, to achieve the desired reproducibility. The whole manufacturing system can be developed to ensure that each employee plays a part in ensuring that each operation done is a correct step to produce the standard required. The controls need not be complicated but they should begin early in the processing and be maintained consistently.             

    Quality Control Guidelines
    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:37:18 AM


    An international approach to Quality Management has developed into various ISO specifications. The procedures are costly and time consuming, but can demonstrate an international standard of production, which is a valuable marketing aid. The system ensures that there is traceability of production process and materials, which helps to identify problem factors.  ISO 9001: 2000 is a Quality Management System and ISO 14000 refers to environmental aspects. The extensive degree of control procedures applies to all stages of product performance, inputs, suppliers etc. Companies wishing to use these systems have to be thoroughly inspected and approved before they can use the ISO marks to show their good production performance. It is expensive to do this in developing industries and a more basic, but thorough, system can still be an effective in-house control. Production should always have a disciplined approach, with individual standards, possibly specified by customers, related to chemical contents or physical properties, and international standards.  

    Quality Control is important for the After Sales service of marketing. It should ensure that the product delivered is acceptable and can be the base for a repeat order, which is essential for successful trading in any product.
    Finished leather needs to be checked for production standards for physical and chemical specification to fit the end use of the leather, as well as to ensure that each colour in a delivery of finished leather is identical to previous deliveries of the same colour. Accurate record keeping is essential and a production manual should cover all the details involved for each production type.


    The production manual is needed to record the standard machine settings and process values for particular products at each stage of production. Measuring equipment has to be accurate and checked regularly. Trained personnel, working within a clearly defined management structure, are essential in the Quality Control system.





    Dehydration. Moisture reduced from 60% to 45%, later to 30%. Ideally sort for size to give narrow process range and better process control and quality.


    To be done as soon as possible after killing, cooling and cleaning. Max. delay 2 h. at 30C. 30% salt on hide wt. Keep dry, in shade, and allow moisture to drain. Avoidseasalt. Recommended for use in damp climate: 5 pt Anhydrous Sodium Sulphate/ 1 pt pure Sodium Chloride (not sea). For longer term, dry after piling. Fold hair in.

    Problems/ Warning

    Red heat colour. Wet feel. Bad smell. Hair loose. Either use the recommended mix above or add bactericide to salt.

    2. SOAK


    Restore moisture to original condition. Critical to quality.


    Uniform temp. all year. 26C ideal, pH 9-10 good. Warmer needs bactericide. Salt conc. not to fall below 2Be (1.0138 SG) to prevent fast action, high swelling and loose leather. 6 hrs. in solution is needed for equilibrium. Do not drum too long. Check completion by folding.

    Problems/ Warning

    Oversoaking: loose hair, Bacteria give smell and slime feel. Loose grain. Undersoak: harsh edge, 'wire' centre.

    3. LIME & UNHAIR


    Remove the hair and open fibre structure for tannage. Important that conditions are constant through the year.


    Uniform temp. 26C ideal. Max. is 30C. Lime maintains pH 12-13. Add sulphide in stages, after some lime.
    Use iron-free sodium sulphide to prevent stains on vegetable.

    Problems/ Warning

    Too long will damage fibres and make leather loose. Too strong alkali causes swelling and draw. The grain can be brittle and crack. Ammonia smell shows degraded hide. Yield changes with process conditions. Main cause of pollution. Black stains show iron present.

    4. LIME WASH


    Clean for fleshing & start delime by thorough washing.


    Wash temp. to be 4C above main lime bath temp. to allow good fleshing and smooth necks. Add 0.5% lime if water is hard to prevent limeblast.

    Problems/ Warning

    Hard water, and delays giving more exposure to air, will cause limeblast, causing stains on the exposed grain. This reduces extensibility and cutting value of full grain leather.



    Remove fat and surplus flesh to give a cleaner surface, good penetration of chemicals.


    Machine adjustment and experienced operators. Trim carefully. Keep all cutting edges sharp.
    Sort low quality for vegetable tannage if feasible.

    Problems/ Warning

    Poor cleaning means poor chemical penetration. Too much loses flanks, so leave some flesh here. Damaged leather from cuts means loss of value. Bad trim means difficulties in splitting, and loss in area (yield).



    To produce a level leather thickness from the different sizes of hides.


    Machine adjustment, experienced operators. Correctly set and maintained machine. Thickness gauge used. Check small pieces before splitting.

    Problems/ Warning

    Unlevel and variable thickness - loss of value. Damaged hides. Limed harder to handle.
    This is the most difficult tannery machine operation.

    7. DELIME


    First stage to replace strong alkali by weak alkali. Swelling reduced, pH adjusted to be suitable for chrome tannage (or vegetable).


    Normally, needs complete penetration. pH to be below 8.5 and cut pelt colourless to phenolphthalein. 28-30C. Temp. limit35C

    Problems/ Warning

    Difficult with penetration on thicker hides (also necks, cheeks) leaves stronger alkali swelling in the centre of hide. Causes harder leather, less yield. (May be left for certain types of firmer leathers). Poisonous hydrogen sulphide may be produced (use 0.5% Sodium bisulphite).

    8. BATE


    Produce a smooth, clean grain by enzyme action, removing non-structured collagen and other proteins. Continues deliming.


    37Ccritical. pH 8.3. Tests for completion by Thumbmark retained in bated pelt and by Air can be squeezed through the grain layer.

    Problems/ Warning

    Under bating means harder leather, without stretch. Over-bating causes looseness, empty flanks, and even loss of actual hide and loss of strength. Grain becomes open and coarse, and can have pinholes, in the extreme.

    9. PICKLE


    Prepare pelt for tanning by changing it to an acid condition. (Salt essential to stop any acid swelling). pH ~ 3 for Chrome tan, pH 4-4.5 for vegetable tan.


    Temp. critical at low pH. 28Cmaximum. Salt concn. to be 6Be (6% salt solution) after 20' run, before acid is added. Indicator on pelt to show little, or a third at most, of less acid section. E.g. methyl orange-red 2.6, yellow 4 (centre pelt) or bromphenol blue-yellow 3, blue violet 4.6 (centre pelt). Formic acid helps penetration. End pH about 3.0-3.3 for Cr.or 3.8-4.0 for veg.

    Problems/ Warning

    Fibres damaged and destroyed by excess temp. and/ or swelling. Acid added in dilute form (10%) and after it has cooled. Time can also be contributory in hot climates.

    10a. VEGETABLE


    To produce an evenly tanned and clean pelt


    Avoid all contacts with Iron surfaces/ shavings etc. Use sequestering salts e.g. EDTA to remove stains.
    Check pretannage and use weaker tannins for the early colouring stages for penetration.
    Start pH 4 and end at pH 3.3.

    Problems/ Warning

    Leather has a greyish shade and Iron stains, which cannot be covered in the final leather.
    Poor tan penetration and overtannage of the grain, causing weak grain and poor quality tannage.

    10b. CHROME


    To produce an even tannage, making leather resistant to putrefaction and usually to boiling water.


    Increasing pH from 2-3 to 3.8-4.0 in controlled stages. Boil test for no shrinkage after 2 mins. May be used (not essential). Bromphenol blue (red at acid pH3 to violet at 4.6) will track pH changes on basification. Shrinkage temperature of leather to be 95-100C.

    Problems/ Warning

    Penetration problems prevent proper tannage. Too acid a tannage is not fully fixed, or boil resistant. Too much alkali makes grain draw and loses quality. Disinfectant is essential to prevent mould, which loses value and reduces trading possibilities.

    11. SAMMY


    To remove the unbound water so that the hide can be split or shaved, with an even and consistent moisture content.


    Experienced operators to avoid damage by keeping the leathers flat, avoiding creases. and achieving optimum moisture levels - by adjusting handling and pressure.

    Problems/ Warning

    Incorrect operations lose value by leather creases, which are damaged in other mechanical operations - splitting, shaving. Inconsistent moisture means that thickness varies from splitting and shaving. Too much pressure dries leather out; too little means leather too wet to handle later.

    12. SPLIT


    As for Operation 6, but this is in the wet blue and easier


    Measuring gauge and skilled operative. Correctly set and maintained machine.

    Problems/ Warning

    Easier than limed splitting but still critical. Need to give even thickness and avoid damage from cuts.

    13. SHAVE


    The final adjustment for thickness (related to orders). An even cutting through a leather with consistent moisture.


    Cutting of correctly set machine with experienced operators. Measuring gauge. Sharp cutting edges.

    Problems/ Warning

    Too thick or too thin. Can easily damage parts and lose value. A skilled operation and second only to splitting.



    To prepare tanned leather for retannage according to the final product required.


    pH gradually changed by weak acid salts. The cut of the leather is tested with bromcresol green (yellow at acid pH3.8 and blue at 5.4) to show the degree of neutralisation. Centre acid section to be up to max. one third only. Actual pH target depends on retannage. Surface neutralisation is >5.0 external, <4.5 internal. Deep neutralisation is 5.5-6.0 external & internal values.

    Problems/ Warning

    Uncontrolled neutralisation prevents correct retannage, making drawn or loose leather - and different fat liquor effects. Reliability means consistent conditions. Control pH, temperature and penetration. Poor condition drums and wrong speeds may cause drawn and pebbled grain, losing value and product appearance.

    15. RETAN


    To produce the type of leather required in the final product by suitable retanning chemicals.


    Penetration and quantities, needing temperature, times and chemicals to be accurately measured. Avoid all contacts with Iron surfaces/ shavings etc. when vegetable tannins are involved. Use sequestering salts e.g. EDTA to remove any of these stains. Chrome containing retannages should be at a minimum, to avoid pollution problems.

    Problems/ Warning

    The leather loses value to the customer as it becomes different to the original order (and sample). A wrong process makes a wrong leather.
    Vegetable retannages are discoloured by iron stains.

    16. DYE


    To colour the leather as required by the customer. This should be an even colour and should cover any grain defects. The colour should be light fast, and wash fast it the finish is not covering.


    All conditions (temp. dye quantity, times etc.). Choice of dyestuffs. Make trial dyeings on small scale and dry out test pieces of the bulk dyeings also. Visible checks on dye exhaustion.

    Problems/ Warning

    Wrong colours, uneven shades, not fast to light, water and drying. Unfixed dyestuffs. Poor penetration. Unstable



    To soften the leather as required by the customer, by lubricating the wet fibres so that they do not stick together on drying. It controls the feel of the dry leather. Usually, the majority of the fat should be the outer layers of the leathers.


    Choice of suitable oil emulsions applied under the correct conditions. Leather should be able to absorb the oil without becoming greasy. Folded wet leather should 'pearl' if processed correctly.

    Problems/ Warning

    Greasy surfaces, highlighted surfaces. Under-f/l gives a hard, dry, cracky leather. Over-f/l means greasy, collapsed leather, often with poor finish adhesion.

    18. SAMM and


    Remove as much as possible of the mechanically held water before drying.


    Experienced operatives. Moist sammying felts and good blades on setting out cylinders.

    Problems/ Warning

    Over-compressed leather means hardness. Creases and damaged shanks lose area and profit. Too little action leaves leather too wet and makes drying difficult.

    19. DRY


    Remove the water without damaging the leather value.


    Temperature, time and handling. Lowest feasible temp. is best for quality and area yield. Moisture meters are a guide but not altogether reliable.
    Vacuum dryers must not dry the leather out completely. Make sure that the damp steaming leathers can be ventilated by hanging.

    Problems/ Warning

    Careless conditions permanently affect the fibres and the leather value.
    Do not store damp leather.


    Quality losses in finishing are accumulative and it is not reasonable to hope that the final correct result can all be achieved by adjusting the last top spray coats.




    Controlled addition of moisture to the fibres, to prepare for mechanical softening.


    A moisture level 18-20%, relative to 'dry' leather having a natural level of 14%. It is important to achieve this by the process pattern being reliable and controlled. Leather is normally held for 24h. to achieve equilibrium, covered in plastic sheeting.

    Problems/ Warning

    Dry leather can easily become loose and damaged in staking. Wet leather (over 20%) is not effectively softened or damaged, and eventually dries out hard.

    2. STAKE/


    Soften by separating the fibres, which have become attached to each other during drying.


    Staking machine settings and operator experience. All to be in the process manual.

    Problems/ Warning

    Excessive action will damage and loosen the leather and under-action leaves the leather hard.

    3. TOGGLE


    Complete the drying, to 14%, and obtain the optimum area by stretching the skin with toggles (clips).


    Experienced operatives. Skin to be flat but not so tight as to damage the flanks. No folded areas.

    Problems/ Warning

    Excess stretching action leaves the leather too hard and the flanks empty, because of chrome leather shrinkage.



    Examine quality and select different grades.


    Experienced sorter and established consistent standards.

    Problems/ Warning

    Process damage is now seen and can be quantified. This % acts as control. Poor sorting standards result in the final product being too high, or too low, in quality.

    5. TRIM


    Remove obtruding leather pieces to minimise further process damage. Should be a positive step for quality


    Leather to be flat and minimum of trimmings; a weight control is useful. Experienced operators and sharp knives.

    Problems/ Warning

    Yield (profit) can be easily lost with over-trimming. Too little allows more machine damage: loss of profit.

    6. BUFF


    Abrade the grain surface of the lower grades.


    Experienced operatives and correct use of papers. Machine settings.

    Problems/ Warning

    Too coarse papers remove grain deeply and lose the surface quality; too fine does not correct the quality.

    7. FINISH (roller, pad, spray)


    Produce the colour and finish wanted by the customer. A very important area.


    Reproducible formulas. Accurate control of mixtures and colours, with pattern cards and samples. Machine settings.

    Problems/ Warning

    The leather will not be acceptable to the customer and loses most of its sales value, producing a loss

    8. PRESS


    Iron, or emboss the surface, with heat producing thermoplastic flow.


    Experienced operatives and controlled temperature/ pressures.

    Problems/ Warning

    Damaged surface and appearance from incorrect machine work.

    9. MILL


    Use of a dry drum to soften thin leathers, such as garment


    Drum rpm and internal condition; leather moisture.

    Problems/ Warning

    Mechanical damage to leather fibres and finish can cause serious loss at a late production stage.

    10. SORT


    Examine quality and allocate each finished piece to a grade. Important that all pieces have a sales outlet.


    Experience and past records, samples. The final quality check before the customer receives the leather.

    Problems/ Warning

    Poor sorting loses money and loses the customer's satisfaction/ future business.

    11. PACK/


    Ensure that the leather quality is maintained during delivery


    Experience and correct materials to prevent damage from creasing and handling.

    Problems/ Warning

    Delivered leather is not acceptable to customer.

    Note well: restrictions on certain process chemicals:   

    There are an increasing number of chemicals, which are now either banned completely, or restricted to certain limits, for leather production due to health or environmental considerations. These include hexavalent chromium, pentachlorophenol (PCP), certain azo colorants, which can lead to certain aromatic amines, formaldehyde and, in some cases, heavy metals such as mercury, cadmium, zirconium.
    It is recommended that chemicals are selected with care to avoid problems later. This is a strong reason for using chemicals from established and responsible chemical manufactures.


    Note well
    that any banned chemical automatically means that a specific control test may be required. All are International Official Methods, as designated.


    Quality requirements

    1. Flexing endurance                                          IUP 20
    Other types of leather
    Laminated splits (over 0.15mm)

    20000 flexes

    10000 flexes

    2. Adhesion of finish                                         IUF 470
    Cattle hide leather, full grain & slightly corrected
    Cattle hide leather, deeply buffed
    Fashionable leather (with thin finish coats e.g. box calf, glazed kid, lamb skin leather)

    3.0 Newtons/ cm

    2.0 Newtons/ cm.

    3. Rub fastness                                                  IUF 450
    Leather for street shoes
    Test fabric dry, leather dry
    Test fabric wet, leather dry
    Leather for shoes without lining
    Inside: test fabric dry
    Inside: test fabric wet
    Inside: test fabric wetted with pH9 perspiration solution
    Fashionable leather
    Test fabric dry, leather dry
    Test fabric wet, leather dry
    Test fabric wetted with solvent-free polish, leather dry

    Rub cycles




    Grey scale

    Minimum rating 3

    Minimum rating 4

    Minimum rating 3

    4. Fastness to hot plating                                 IUF 458
    Patent leather (hot air test with leather extended and lacquer coat perforated)

    Minimum 80C

    No cracks

    5.Distension of grain                                        IUP 9

    Minimum 7.0

    6. Split tear force IUP 8
    Leather for lined shoes
    Leather for unlined shoes

    Minimum 18 N
    Minimum 25 N

    7. Extractable with dichloromethane              IUC 4
    for one-component adhesive
    for two-component adhesive
    for special polyurethane adhesive
    for vulcanising
    for PVC mould-on

    Up to 9%
    Up to 14%
    Above 14%
    Up to 8%
    Up to 15%

    8. Water resistance test (as required)           IUP10
    Upper leather for winter boots
    Other shoe leathers
    Waterproof leather

    Water penetration
    Minimum 60 mins
    Minimum 30 mins
    Minimum 120 mins

    Water absorption
    Maximum 35%
    Maximum 35%
    Maximum 25%

    9. Light Fastness (as required)
    IUF 401 - daylight
    IUF 402 - xenotest

    Minimum rating 3
    Minimum rating 3

    10. Cold flexing endurance (as required)        IUP 20
    Special leathers at -20C

    30000 flexes


    Quality requirements

    aniline leather

    finished leather

    1. Rub fastness                                                          IUF 450

    rub cycles

    test fabric stains

    Leather dry/ test fabric dry


    > rating 4

    > rating 4

    Leather dry/ test fabric wet


    > rating 3

    > rating 4

    Leather wet/ test fabric dry


    > rating 3

    > rating 4

    Leather dry/ test fabric wetted with perspiration at pH 9


    > rating 3

    > rating 4

    Leather dry/ test fabric wetted with petrol (BP 80-110°C)


    No staining

    2. Elongation at break                                              IUP 6
    minimum leather thickness >0.4mm
    Skivers, unlaminated
    Skivers, laminated
    Other leathers

    Minimum 25%
    Minimum 30%
    Minimum 30%

    3. Soluble mineral salts                                           IUC 6

    Not over 1.5%

    4. Extractable with dichloromethane                   IUC 4 Lining leather
    Lamb woolskin leather

    Maximum 10%
    Maximum 8%

    5. pH value IUC 11

    Not below 3.5

    6. Split tear strength as required                         IUP 8

    Only Lining leather for reinforcement.
    Min. 15 N


    Quality requirements




    1. Rub fastness                                   IUF 450

    Rough leather

    50 rub cycles

    20 rub cycles

    20 rub cycles

    Grey scale contrast

    Maximum rating 3

    Smooth leather

    500 rub cycles

    80 rub cycles

    50 rub cycles

    Grey scale contrast

    Maximum rating 4

    2. Light Fastness

    Minimum rating 3

    3. Flexing endurance                         IUP 20

    20000 flexes

    4. Adhesion                                         IUF 470

    2.0 N/cm

    5. Split Tear force                               IUP 8

    20 N/mm thickness

    6. pH value                                            IUC 11

    Minimum 3.8

    Note: Car Upholstery will have different specifications for individual companies and will include fogging (volatiles at 75C or 100C) and abrasion tests.


    Quality requirements

    Aniline nappa, suede leather, nubuck

    Nappa leather, finished

    1. Light fastness
    daylight              -             IUF 401
    xenotest             -             IUF 402

    Rating 4
    Rating 3

    Rating 4Rating 3

    2. Rub Fastness             IUF 450

    Rub cycles

    Felt dry
    Felt wet
    Felt wetted with pH9 perspiration



    3. Flexing endurance      IUP 20


    > 50000

    4. Adhesion of finish     IUF 470

    > 2.5 N/cm

    5. Split tear strength     IUP 8

    20 N/mm

    30 N/mm

    6.Tensile strength          IUP 6


    12 N/mm²

    7. Wettability                   IUF 420

    10 minutes

    15 minutes

    8. pH value                       IUC 11

    Minimum 3.5

    Minimum 3.5

    LT.1.3. - Pricing

    Contributed by: Mr. Woodley, Michael
    International Consultant,

    Last updated: 24/05/2007 11:38:37 AM

    Leather production is a conversion process, starting with a raw material, which may be in different forms.  The production chain, converting raw material to product, needs money to be spent at every stage. These individual costs have to be known and controlled to obtain an accurate final cost price, ex factory, so that a profitable sales price can be decided. There is a viable minimum size for a tannery, related to the equipment being used for the full working day. This corresponds to about 350 hides, or 2000 skins, per day for a single shift of 8 hours. Partly used equipment is uneconomic because its costs, on unit allocation, are higher than equipment used longer.
    New equipment costs for a tannery, producing 12,000 square feet of finished leather per day, is estimated at about US$ 2.0 million; this compares with a wet blue operation, of the same input, costing about half this sum. Both sums include chrome recovery and effluent pre-treatment plants estimated at US$ 280,000 (for sulphide aeration, separation of solids by centrifuge, but not for any biological treatment). In addition, there should be an allowance of 15% to cover initial spares, shipping and installation costs.
    In comparison, new equipment for a skin tannery for finished leather, producing 10,000 square feet each day, is estimated at US$1.3 million; wet blue production is US$ 560,000. Effluent treatment is estimated at US$130,000. Again, there should be a similar 15% allowance.   

    Although the raw material price alters with market conditions, which are mainly outside the buyer's control, the conversion costs for the product are within the tanner's control and need to be carefully monitored.                       

    These conversion costs are allocated over the whole planned production, on a unit area basis (usually per square foot), according to the work done.  There are two classes:  

    • Variable costs, which alter in direct proportion to level of activity. These are chemicals, power, water, effluent treatment, maintenance of equipment and buildings, distribution, delivery and labour. They are calculated for each type of product, from the process details, and relate to all stages, wet blue, crust or finished.
    • Fixed costs, which remain unchanged despite changes in the level of activity, and are allocated over the whole estimated production volume for a set time. These have to cover the depreciation of investments in buildings and equipment, as well as loan repayments, and the costs of holding stocks and work in progress. The forecast volumes for production, in the budget, need to be realistic to ensure there is a complete recovery of all fixed costs.  

    The total conversion costs are then added to the raw material cost to give the estimated production cost of each type of product. If the total costs are only averaged over all products, the comparative actual costs for each product are not related to the sales value. This can lead to sales, which are actually a loss to the tannery, but are not recognised as such. If lower quality leather has to be sold below cost, it is important to ensure that there is sufficient compensation for the loss, by selling better grades at a higher margin. The aim is a net profit from all products and grades.
    The most important fact is to appreciate how tannery costs vary.


    Supply and demand affects market price levels. Because the supply of raw hides and skins is fixed as a by-product of the meat industry, there is no relation between the supply available and the actual leather demand. This can result in great variations with the raw prices reflecting the changes in demand from tanneries for an inelastic source. In the long term, leather prices rise and fall like all commodities. Fashion is a factor, for example, with such demands as kid leather, suede for shoes or clothes and the value of splits.
    Non-leather materials act as a cushion to rising leather prices by providing an alternative supply but they are really also a strong competitor to replace leather altogether. However, the non-leather materials are based on petrochemical and oil sources, and so they are not sustainable compared with natural by-products from livestock resource, in the longer term.   There are trade cycles and major problems, such as droughts, floods, disease (BSE, Foot and Mouth) have global effects.  

    Raw hides and skins are sold per piece, or by weight, but leather is sold by area. The relationship of the respective areas produced from different raw materials is important to allow any true costing, and should be a main cost control. Known as the 'Yield' it relates final sales area to the input weight.
    An example is that of a wet salted hide, which costs $2.50 per kilo with weight of 12 kgs. and corresponds to a purchase price of $30 per hide. If the final processed area is 24 sq.ft. the yield is 2.0 (24/12), which makes the raw material cost $1.25 per sq.ft. However, if processing produces only 23 sq.ft., the yield would be 1.92 (23/12) and the cost of the raw material becomes $1.30 per sq.ft. Profit would be reduced by this amount plus the fact that all other costs are increased when the size is that much smaller. This shows the importance of yield control and the dangers of losing the planned area and profit. An operator can easily lose some of the area on a hide, or skin, by damage or excessive trimming.
    The split, taken when the levelling is done, can have be given a relatively small value of hide as a cost allocation e.g. 15% of hide by weight becomes split, corresponding to 25% by area and takes 5% of the hide cost. This reduces the raw cost for the grain split by 5% and is significant. Alternatively, the split may be processed without any raw material cost allocation. This decision will depend on the state of the market for split leathers, which is always below the cost of the actual hide.
    More details of this critical yield control are shown below.            

    Each method of selling the raw has variables and it is important to have as uniform a selection of size, weight or moisture content, as possible. Each weight category of hide, or skin, has a different thickness and so a different yield calculation.  Each individual skin has different characteristics.
    Raw material prices have to be compared knowing the different yields, so that buying can be well informed. The different shapes all have to be finished as flat pieces and sold on the basis of area.
    Any change in the condition of the raw material or the processing affects the yield and, therefore, the profitability. This means the chemical and physical treatment given. The yield is, normally, the area produced from a unit weight. There are other yields, as suits the tannery for other productions. It always relates the output unit of leather related to the input unit.
    All calculations and costing need to have reliable yield information to give reliable costs before the sales price can be known to be profitable. The example above shows how the cost is affected.
    At least half the final cost of the leather is related to the purchase cost of the raw material, so a poor purchase of raw hide can eliminate all potential profit from the leather. It is important to have the expected yield figure relating to the type of material to know the expected raw cost per unit area, when buying raw.


    All initial costing and evaluation is based on experience as to the average quality and value of leather made from that type of raw material. In practice, no two hides or skins are the same because they reflect the physical condition of individual animals. Every '100 pieces' will contain a range of quality. The size and weight is an indication of animal age, but it is not feasible to know the different grades in the raw, apart from obvious cuts, holes and state of preservation. The purchase of raw material needs experience to assess approximately the proportion of quality grades that will result from processing.    
    After unhairing and tanning, the surface grain can be seen more clearly for any damage, which explains the value of wet blue sorting.
    However, the marketing of the raw material quality must be done by offering reliable grades, related to leather qualities.  

    The tannery sorts the '100 pieces' several times, in the production process, to decide how to obtain the most value and to meet the demands of the market. If the sale is in the wet blue, then there is only one sorting. However, if there is to be further processing, then there will be a second sorting in the crust and then later, for the finished leather. As grades are sorted, they are often processed differently to produce different types of leather. Ideally, the decision as to the type of leather to be made from a particular piece of hide, or skin, should be delayed as long as possible in the processing. It is more difficult to decide in the wet blue than in the dried crust.


    The control figure mentioned above can be made at different stages and on different conditions of material, as shown in the example below.

    Fleshed weight

    Final sales area



    2.5 kilos

    6 square feet






    Buffalo calf












    Moisture content is variable in many processes, but the fleshed weight should represent a fully re-hydrated hide or skin, consistent in moisture if weighed promptly and with comparable draining times. It often provides the first opportunity to judge the actual useful material from a particular purchase and the start of a yield control for production, to ensure that area is optimised.
    Different drying methods have a large effect, e.g. hanging compared with a vacuum drier, as do different levels of trimming. Vacuum gains up to 7% over hanging, and re-toggling a re-conditioned leather shows a gain of 1.3% compared with a leather with no extra conditioning at all. Area is always affected by atmospheric humidity. 
    Trimming of the overall shape, by a knife, may be to assist machine operations or to improve the sales appearance by removing low grade areas; in all cases the area lost means that there is loss of sales income, reducing profit. Odd shapes and pieces do not have any sales value because they have no cutting area; so they are a loss to the customer, who would prefer the leather to be all a useful shape.
    Final yield comes from the final sorting. This means that the hides and skins need to be traced to the original purchase markets, to relate accurate costs. In practice the leather may be finished several weeks after the raw was purchased.


    The process chemicals are calculated on the basis of the recipe, allowing for any possible loss or spillage. A very detailed approach allows a much tighter control over chemical costs and allows a more competitive sales price to be quoted with more confidence.
    Such calculations also allow the correct evaluation of any process trials to improve quality. The extra cost of an alternative process is calculated and compared to see if it is more than reimbursed by the extra sales value of the leather.

                a) Wet Blue tannage

    The following calculation is an example of the chemical cost for producing wet blue - including all pre-tanning operations in a basic recipe.
    The % offer of chemicals is based on the input weight of salted hide.



    Kgs. chemical
    per 100 kgs

    US$ per
    Kg. chemical

    $ Cost per
    100 kgs. hide


    Sodium carbonate










    Slaked lime





    Sodium sulphide (66%)





    Ammonium sulphate





    Pancreatic bate





    Sodium chloride





    Sulphuric acid





    Chrome powder 11/33





    Sodium formate










    Basifier as MO




    TOTAL - no spillage


    Spillage etc + 1%


    TOTAL - with spillage


    Each process stage has a specific yield related to the input weight. For the wet blue, we can use the yield from the raw of 2.0sq.ft.per kilo. This would mean that 100kgs. Input hide yields 200sq.ft and the tanning to wet blue costs 8.05 US cents per sq.ft.
    The relative costs of the chrome and the fungicide are highlighted here. Fungicide is important and critical in warm, humid countries for leather and leather products.  

    Note: If there were no spillage there would be a further contribution to profit of 0.08 cents per sq.ft. ($3.2 for a 40sq.ft. hide). 

            b) Retannage costs:

    These chemicals are for a simple low cost process, based on shaved weight, and calculated for processing 100 kg. shaved weight hides.



    Kgs. Chemical per 100 kgs.

    US$ per kg.

    $ Cost per 100 kgs. hide


    Sodium bicarbonate





    Basic syntan










    Formic acid





    Fat liquor




    TOTAL - no spill


    Spillage etc + 1%


    TOTAL - with spillage


    This will have a different yield. For example, 1kg of wet blue hide shaved to 2.0 mm, will yield 4.5sq.ft. Using this yield, a simple retannage cost will be 5.99 cents per sq.ft. Many retanning chemicals are more expensive.

                c) Finishing chemical costs.

    These operations are on the dry leather and need to be calculated from the application rate, the material used per square foot, not from the % basis of wet processing. Waste allowance is even more important because of the practical fact that liquids are used and there are always residues to be dealt with. (10% is calculated below.) Similarly, coating and spray machines have an extra quantity lost in the machine, or wasted in overspray. The quantities are significant (25% used below). There are economies possible for long colour runs and disadvantages from short runs and samples, where wastage is higher.
    Some examples of the costs for different operations, simple finish, are:


    Solution cost
    US$ per litre

    gms. /sq.ft.

    Cost in US cents
    per square foot

    Cost with
    10% waste






    Pigment - coat 1





    Pigment - coat 2





    Pigment spray 1





    Pigment spray 2





    Top coat







    Cost comparison of all above operations per sq.ft. finished leather
                d) Operation cost comparison


    Cost in US cents












    In practice, the retannage and finishing costs are usually more than tannage cost.


    Total costs of all personnel are spread over the whole production, unless there are certain sections producing more than others; for example, when wet blue is the main output and finishing the minor output.
    Low labour costs have promoted the concentration of most manufacturing, including the leather sector, to Asia and particularly China. The entry into the world economy of China, India and the former Soviet Union has doubled the global labour force. China is responsible for 50% of the extra personnel. This has promoted out-sourcing and will continue to do so.
    However, low labour costs do not mean low production costs if the productivity is low. Mass production tanners have a good productivity of 40-50 sq.ft. per man-hour, but a varied production generally has about 20 sq.ft. of leather produced per man-hour.
    The West European minimum wage level in 2006 is about US$9.6 per hour (Federation of European Employers). This means US$0.48 to US$0.20 labour cost per sq.ft. of leather for different productivities. This is not competitive for leather, which has to sell at $1.50 per sq.ft., particularly when the actual average wage is about double the minimum rate.
    Some minimum rates of pay are shown below with their comparative labour costs per sq.ft, calculated with a productivity of 20 sq.ft. per man-hour. It is unlikely that superior productivity can make production in Eastern Europe viable as a producer; Romania is exceptionally low for Europe and Shanghai is the most expensive city in China. High labour costs can only be justified by high added values, as in the top quality niche leathers.


    $ hourly rate

    $ cost per sq.ft

    % of leather cost,
    if $1.50

    East Europe








    Shanghai and Bulgaria




    At $1 per 8 hour day




    Economist June 2005, based on gross wages for 2003
    Source: IMF, China Daily

    The skill required varies with the machine. It is very important for quality because damage is easily caused and the value lost. Rates of pay should reflect the relative levels of skill - unskilled, semi-skilled and skilled - from drum hands to splitting master, considering the potential for damaging the material and the loss of value. Limited repairs are possible to most damaged leathers but there is always some loss incurred.
    The value of a finished hide is about $50 and a finished skin is about $8; this is more important than minimising the labour cost. There is a need for all workers to understand the worth of the material and not to treat it as waste.


    Fixed overheads will have to cover the depreciation of investments in buildings and equipment, as well as loan repayments, and the costs of holding stocks and work in progress.
    Variable overheads, related to a variation in production level are power, water, effluent treatment, maintenance of equipment and buildings, distribution and delivery.  

    Basic planning data is that 1 tonne (1,000kgs.) wet salted hide processed to finished leather needs -  

    • Area of 500m², with 350m² for production and 150m² for non-production (including stores, offices and maintenance workshop).
    • Process water of 40-60m³, reducing to about 20m³ with best practice. 70% is for processing up to the wet-blue stage. 70% of the total becomes effluent, after allowing for evaporation. 
    • Steam of 2,000 kg., which is mostly for production of retanned dry leather in colder countries.
    • Power of 700kWh electricity. One third is estimated for wet blue, crust and finishing respectively.


    When production is completed to a particular stage for selling, a variety of raw material grades have been manufactured into a variety of different products, or at least a variety of grades of the same product. Each grade carries its own intrinsic worth, to which the production costs have to be allocated. The sales prices have to be balanced to reflect the different cutting values of the grades and their costs, so that the overall sums show a profit for the original 100% input or raw material.
    A possible scheme for original sorting, best done in the crust, could be -

    • Grade 1: Only 10% of grain damaged - suitable for transparent (aniline) finish
    • Grade 2: 10-30% defects - suitable for semi-covering finish
    • Grade 3: 30-50% defects - full cover, pigment finish
    • Grade 4: Over 50% defects - corrected grain, embossed or special upgrading covering finish
    • Grade 5: Rejected due to putrefaction or extensive damage.  

    The grading is related to the good cutting area of finished leather, provided the leather has the right thickness, colour, feel and finish appearance. Quality is assessed by the clear cutting area available on the surface of the leather and the grades are evaluated in proportion. The target for good marketing, and product development, is to develop a profitable product from each grade, or mixture of grades. This demands good technical competence for such development.  Consequently, a large pattern for shoes or large bags is more demanding than smaller items like wallets. Pattern cutting dictates the profit potential for the finished leather buyer and so influences buyers for semi-processed leather also.
    As the tanner sorts the different pieces several times, the lower qualities are all priced below the average, whereas the higher are above the average. The difference in quality grades is related to the varying amounts of each grade in the 100 pieces (for example 10%, 40%, 40%, 10%). The overall result has to give the profit margin based on the total grades and prices. Lower grades often have higher tannery production costs and so are not sought after in normal business. Any loss due to substandard material has to be covered by the profit on other grades. If the lowest grades are unsold they become a continued loss on the stock values of the tannery and cannot be ignored. The upgrading of lower grades receives a lot of attention.
    The example in the table shows how the profit contribution varies with each grade and the value of quality at all stages.






    Mean for 100

    % cutting value






    % production in each selection






    Sales price scale






    % profit - on overall cost of 70




    - 4


    Profit contributed pro-rata for 100






    The lowest grades may not be wanted in the export market, but can have a useful outlet in the local small-scale productions of leather goods and leather footwear.
    The alternative is that they have to be sold below the processing cost. The higher profit margin on the better grades compensates for the lower prices (and profit) on the lower grades, as shown above.
    In this way, the struggle to raise quality can always be assessed as to whether extra production costs are more than covered by increases sales income.            

    The marketing target is to sell each product from a specific grade of raw material at a profit, or at least, to sell the total combined grades, originating from the raw, at a total net profit overall.


    Trading and working with such a natural material, which will rapidly deteriorate outside narrow process conditions until it is tanned, needs a lot of care and experience. Such risks ought to be accompanied by generous trading margins, but competition is so severe in the bulk market that margins are usually narrow. This shows the need for good control of costs.  

    Two classes of entrepreneur can start a business with some reduced risk:   

             a) A raw hide trader has a reduced risk if he enters the sector because he has knowledge of the raw market and respective values. He knows when to buy and when not to buy. 
             b)  A competent leather technologist with established customer contacts for his products has a reduced risk provided he can obtain a margin on the costs.  

    Although, raw hides and skins are a by-product of the meat industry, the raw price is affected by demand for leather related to the available supply. The supply volume is only dependent on the meat market. Price levels do change. This volatility is a serious risk when there are large stocks, including work in process.       
    Production processes can be measured in days; wet blue production is about 5 days and finished leathers about 3 weeks. Strong efforts are being made to reduce such process times and to reduce the time for stock turnover. Bank facilities are important to finance the stock.
    Long credit times are prevalent and tanneries are caught between the need to pay, often in advance, to secure the raw material whilst they are waiting to receive payment from their customers. The raw material purchase is critical to a profit and there are many successful tanneries which have been established from hide dealers. Credit may be based on the value of the raw material.
    The actual surface quality of a raw hide and skin (the 'grain') cannot be seen until the hair has been removed in process. Consequently, only experience can allow for this unseen factor, accepting that a variety of grades will result. Wet blue has the advantage that the surface can be clearly seen, although the effect of the processing is not known.
    Buying semi-processed material is a risk unless the actual condition is known, from experience. Incorrect processing could cause severe problems with looseness and general appearance. In practice, this risk is minimised by evaluating a sample on a trial basis.
    The main risk to producers is the inability to sell the lowest grades of material reasonably, such that the composite of all grades cannot reach a profit. The essential object of any successful marketing is to sell each grade of material at a profit and, certainly to have a net profit on the '100 pieces' of original material.    


    The purpose of this chapter of the Leatherline Guidebook is to make the reader aware of the machines that are needed and used in the tanning process. A logical sequence will be followed based on the actual tanning process itself. Some machines are used in more than one sector of the process, but distinguish themselves from sector to sector with characteristics that are specific for each sector, and hence will be mentioned separately. A liming drum is different from a tanning drum, although they are both drums, similar but not the same. For each machine in each sector, this chapter of the Leather Guidebook will give the general specifics and indicate the action exercised by the machine(s), and to what purpose. The field of tannery machines is extremely vast and some machines are so specific, that not all machines can nor will be represented in the Leather Guidebook as off the beginning. At this stage the Guidebook does not yet deal with machines that are used for the processing of leather with hair or wool.

    Since this is an open source, each reader can contribute with his knowledge items and paragraphs. Below the reader will find a summary of machines with essential drawings and pictures,. A technically more detailed overview for a number of tannery machines is published by Assomac, the Italian Tannery Machine Manufacturer's Association, who have generously permitted the publication of their drawings on this website.

    It is obvious that bigger, sturdier and larger machines are required for hides than for skins. Machines come therefore in a large number of construction variations and working widths depending on the type of raw materials for which the machine has been specifically designed. This machine guidebook neglects such differences in structure, in the working width and in the power needed to deal with hides or skins. The working principle of the machine is the same for both hides and skins. Apart from this, each manufacturer constructs its machines based on their know-how, their in-house research and technical development, which makes their machine different from machines produced by competing companies.

    Many machines have accessory machines which have more to do with automation, than with the tanning process. There are machines that come in two versions, reverse and feed-through, in which reverse means that the leather is being fed into the machine at one end and taken out of the machine at the same end, whereas a feed-through machine has the leather entering at one side and exiting at the opposite side. The feed-through or reverse feature is important for the productivity of a machine but from the leather technological point of view this makes no difference and will therefore not be treated as two different machines, which they are in reality.

    This chapter will (as yet) not deal with stacking machines, selecting machines etc, as they are not directly involved in the actual basic tanning or finishing process.

    The machine photographs on this website have been published with the permission of the manufacturers. Since this is a non-commercial website, all references which can lead to the manufacturers have been covered or deleted on purpose.

    MA. 1.1. - History

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Processing hides and skins is a combination of chemistry and of mechanical action. When there were neither composite chemicals as the industry uses in present times, nor machines to physically manipulate the leathers,  hides and skins were nevertheless transformed into leather. From the beginning of times mankind hunted animals to feed on and used the skins of the hunted animals for protection against the elements.

    Skins were also used to write on. Treatment of skins for parchment was simple. The skins were de-haired, cleaned of excessive flesh and then dried on frames. Hides were used for saddles and armoury. In the Middle Ages leather, not just raw hides and skins, becomes an important part of every day's life. It is used for belts, bags, hats and of course shoe ware. Instead of composite chemicals people used leaves and other extract of vegetable origin, faeces and urine, whereas the mechanical action of tanning was performed by poles that were poked into the hides and skins in  the afore mentioned "chemical" bath. Dante Alighieri mentions the leather "industry" in his verses. Florence had tanneries alongside the river Arno already in the 13th century. A town like Paris featured extremely smelly tanneries on its now legendary bridges ("The Perfume" by Patrick Suskind). Independently from the moment in history, the tanning process required always and still requires large quantities of water.

    The Moroccan town of Fez, (picture left provided by "Tourism Morocco Milan") a Unesco heritage site, has become a famous tourist attraction because it displays in present times the traditional way of tanning skins, complete with the characteristic smell. In many West African regions Moor women and men still produce in their traditional way vegetably tanned leather.

    The first real tanning chemicals were vegetable extracts generated from leaves and bark, which were only later partly replaced by, or used in combination with synthetic chemicals. With the industrial revolution also tanneries replaced step by step, where possible, pure manpower with machines. With the help of modern chemicals and sophisticated chemical processes, combined with technologically advanced machinery, the process of tanning has abandoned the artesian approach and displays now a very technological industrial concept.(picture Arcapelli)

    The tannery is divided in four main sections, being soaking and liming, then deliming, pickling and tanning, after which retanning and dyeing, and in the end finishing. All starts however with the raw material, the raw hides and skins, being the by-product of the meat industry. 

    The following pictures have been kindly put at the disposal of the International Trade Centre by several sources which are mentioned and who all claim copyright. This is to show old time tanneries and/or machines. This is an open source website and whoever has interesting photo's is kindly invited to send these to the Leatherline webmaster, who will publish them.

    Created by:LANCEY, Ms. Raphaelle 21/05/2007 10:39:49 AM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:45:29 PM

    MA. 1.2. - Raw material section

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    In the raw material section hides and skins are prepared by conservation for the leather process. Ample descriptions can be found in the RAW MATERIALS chapter of the Leather Guidebook.

    1.2.1. Fleshing machine

    When hides and skins are removed from the carcass in an abattoir, some meat and fat remains attached to them. Fat and meat are unnecessary ballast in the tanning process, so these are removed in order to obtain pure leather and save water and chemicals in the process.

    When removed before the conservation process is started, the salt-free fat and meat have an industrial value, and are usable in the cosmetic, pharmaceutical and the food industries. In places with a high productivity of hides and skins, like large (city) abattoirs, hides can be fleshed in green, e.i. in the fresh state immediately after being removed from the carcass.

    The operation requires a fleshing machine with specific blade and pressure rollers.The fleshing machine runs a very fast rotating cylinder on which a number of stainless steel blades are embedded. The hide, once introduced into the machine is being pressed by special rollers against the rotating blades which scrape the flesh and fat from the hide.

    1.2.2. Salting Drum

    In the Raw Materials chapter of the Guidebook in chapter HS.P.1.4 it was mentioned, that hides and skins need to be conserved to avoid putrefaction. One of the methods of conservation is salting. Salt can be applied to hides and skins in a variety of ways. One of them is to load the raw materials into a drum, add large quantities of salt, and run the drum for several hours in order to evenly apply the salt to the raw materials. Drum salting is a rather quick method of salting and is suitable mainly for large quantities of raw materials.

    Drum salting requires expertise from the operators, because the friction of the raw materials and salt inside the drum generate heat and heat is the arch enemy of good quality conservation. A normal wooden drum can be used. In most cases producers use old drums due to the extremely corrosive effect of the salt on any of the metal parts of the drum. Stainless steel drums are also used due to their better resistance against corrosion.

    1.2.3. Desalting Drum

    Salt is 100% soluble in water and is difficult to eliminate from water once dissolved.

    Salt is considered a polluting factor in effluent, hence the less salt is contained in the effluent of the re-hydration process, the less the effluent is polluted. Tanneries have therefore a need and an interest to eliminate as much salt as possible from their raw materials before they are brought into production.

    This can be done by hand, which is a very tiring and time consuming process, or by machine, e.i. by the de-salting drum.Hides and skins are loaded into the desalting drum which by rotating enacts, by using friction and the force of gravity, a separation of the salt from the raw materials. The salt falls to the ground through large open space in the drum, and can be reused if refreshed with new salt. Although he process is simple and the drum is relatively cheap, and the benefits in terms of pollution quite important, not too many tanners actually de-salt.

    Created by:LANCEY, Ms. Raphaelle 21/05/2007 12:56:55 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:46:03 PM

    MA. 1.3. - Soaking and Liming Department


    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    In the soaking department the raw material is being re-hydrated to bring hides and skins to an optimal level of moisture, opening up the fibres to allow at a later stage the best possible penetration of tanning chemicals. Liming provides for the first transformation from raw material to leather.

    1.3.1. Pits

    When tanneries did not have drums, the whole tanning process was done in pits. Pits were some form of  water proofed containers. In modern tanneries pits, normally made in cement or concrete, are still used but mainly for re-hydrating skins (goat and sheep) although many, even modern tanneries use pits also for liming. Pits can be static, hence a container for water to which the skins are added to absorb sufficient water that allows the fibres to open enabling the chemicals and enzymes in later processes to penetrate suitably. Pits can be dynamic and have a rotating wheel that moves both the water and the skins. It is obvious that pits with paddles  provide for a faster and more even distribution of the re-hydrating liquid (water) over the skins. The position of the wheel in a pit or paddle is of crucial importance for the proper flow of water. The axis of a wheel is at the position of one third of the depth (not to confuse with the height) of a pit.

    1.3.2 Paddles

    Paddles are an evolution of the tanning pit. Simplifying one can say, that a paddle is half a drum. The paddle is static but has a wheel positioned in such a way to guarantee a suitable flow of the water and movement of the skins inside. This favours an acceleration of the chemical process which was operated in the pits. Today paddles are less used as most tanneries soak in drums. However for furskins paddles are imperative in order to avoid the clotting of the wool. Drum soaking for this type of skin is too violent.

    1.3.3 Dehairing machine

    After skins are soaked either in a drum or a pit, and in case it is required to recover the wool or hair of the skins, the same are "painted" on the flesh side with a chemical solution that promotes the detachment of the hair or wool from the skin proper. The chemical solution can be either sprayed or hand painted on the skins. After a period of 6/8 hours the hair/wool can be removed from the skin either by hand or by machine. The de-hairing machine is very similar to the fleshing machine, with the difference that the blade roller acts on the side of the hair instead of the side of the flesh and with blades that are not sharpened. The blades actually "scrape" the wool or hair from the skins.

    1.3.4. Drums

    Drums in the liming department are generally the largest in a tannery. They can reach sizes like 4x4 metres and more. The size is of course established based on the production needs of each specific tannery. Liming drums can be larger than high. Two types of drums can be found, namely wooden drums and fibreglass mixers, which are very similar to concrete mixers. Liming drums are turning slowly (2-4 revolutions per minute) and are usually working connected to timers. Depending on the process and formula that is being executed, a liming drum may run for a couple of minutes per hour only, but for an extended period of time, generally more than 24 hours.

    Hence the need for a timer. Liming drums, like their equivalent in the tanning and dying sections have a number of accessories, which can be an automatic door or automatic draining valves. Since wool or hair can be chemically removed from hides and skins in the liming drum, one of the important accessories, that exercise and anti-pollution function is a device for hair recovery. Inside drums can have either pegs or shelves or a combination of the two, which are designed to move the hides upwards inside the drum and once they reach the top of the apex, they drop back into the tanning bath, which is practically the mechanical tanning action.

    1.3.5. Fleshing machine

    After liming and before de-liming hides and skins have to be fleshed in case they have not been fleshed in the raw (paragraph 2.1). Most tanning processes consider lime fleshing. Flesh and fat are removed by blades which are mounted on a fast rotating cylinder. Pressure rollers push the hide or skin against the blade roller. The sharpened blades cut the meat and fat from the hide, without of course damaging it. Today's modern fleshing machines are hydraulic and equipped with sophisticated mechanical and electronic aides. These ensure that hides and skins are properly cleaned of fat and meat independently of the thickness of the hide or skin in question. Not only from one piece to another piece, but also on one and the same hide, where normally the bellies are thinner than the backbone and the neck portion. A system of rollers push the hide with the flesh side against the fast rotating blades, which scrape off the fat and meat from the leather without damaging the leather.

    1.3.6. Splitting machine

    Depending on the final product tanners can opt to split their hides in the lime. Splitting is the operation that separates the top layer (grain) of a hide from the lower layer (split)  by passing a hide between rollers onto a fast rotating band knife that effects the separation in the section of the hide. Splitting machines are sophisticated high precision machines and are today all hydraulic and electronically controlled. The splitting operation, which acts on a tenth of a millimetre and better, is one of great delicacy as both the top layer, the grain, and the lower layer, the split, must be of uniform thickness and totally smooth without cutting marks from the knife. All splitting machines are of the through-feed type. The lime splitting machines features a specific type of rollers, which are different from those that are used for wetblue or dry splitting (4.3).

    Created by:LANCEY, Ms. Raphaelle 22/05/2007 2:32:45 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:46:34 PM

    MA. 1.4. - Tanning Department

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    In the tanning department raw hides and skins become for the first time leather through a mechanic-chemical process.

    1.4.1. Drums

    Tanning drums are similar to the drums in the liming section and in general of similar size with the same diameter and width. They rotate however faster (about 8 revolutions per minute), and contrarily to the liming drum, tanning drums, once started, continue to rotate until the end of the process, with only periodical stops that allow for chemical checks and chemical feeding. Tanning drums can be made either of wood or of fibreglass in the form of (concrete) mixers. By means of gearboxes and inverters, drums can be rotated in forward and backward direction and at different speeds.

    1.4.2. Sammying machine

    The Sammying machine is meant to squeeze a large percentage of liquid from the tanned hide or skin. This either in preparation for shipment or in preparation of splitting. The sammying machine consists in principles of two felts, an upper and lower felt, between which the hide or skin is squeezed and metrically extended towards its perimeter. The actual squeezing action is performed by a system of hydraulically steered cylinders, the extension by rollers which are also position and acting in a way in order to take out folds.

    1.4.3. Splitting machine

    When a hide has not been lime-split, it is usually split into grain and split in tanned condition after being sammyed. The splitting machine for tanned hides is very similar if not the same as the lime splitting machine, with the exception of the rollers that hold the hide for the splitting operation. Splitting can be done also in crust condition (par. 7.4). All splitting machines are of the through-feed type. The actual end product that tanners wish to achieve determines whether splitting is done in lime, wetblue or dry condition.

    1.4.4. Siding machine

    Hides can be sold either in full pieces or in sides. In order to obtain sides, one cuts the hide right over the spine in a left side and a right side. This operation can be done by hand or by a rotating blade. The rotating blade system is similar to the principle of wood sawing. It is to be mentioned that there are other methods of cutting a hide, which is general done in raw condition and by hand. This different method cuts a hide in 3 or 4 pieces: a collar and two culattas, or a neck and two bellies and a croupon.

    Created by:LANCEY, Ms. Raphaelle 22/05/2007 3:13:44 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:46:50 PM

    MA. 1.5. - Retanning Department

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Retanning prepares the leather from leaving the wet stage and enter into the dry stage both by chemical and mechanical manipulation. The leather is given shape and substance, as well as the principole characteristics it requires as a finished product.

    1.5.1. Shaving machine

    The purpose of the shaving machine is to bring pre-processed hides and skins (in whatever type of tannage) to the required and uniform thickness as required by the specifications of the finished leathers. Hides and skins are shaved at the flesh side by sharpened shaving blades which are fixed on a fast rotating cylinder. The leather is pushed by hydraulic pressure over moving rollers against the shaving blades which are in general electronically calibrated in order to achieve the required thickness. Shaving machines are rather sophisticated in order to ensure an even thickness throughout the leather. As mentioned before hides and skins are by nature thicker at the backbone and neck, and thinner at the bellies, hence the machine must take that into consideration.Shaving can be done also when the leather is in dry condition (7.3)

    1.5.2. Drums

    Drums in the retanning, and dyeing department are similar to the drums in the tanning section, but generally smaller and usually with a diameter that is bigger than the width. A typical dyeing drum measures 2.50x1.80M. They rotate more or less at the same speed as the tanning drums, and once started, continue to rotate until the end of the process, with periodical stops that allow for chemical checks and chemical additions. There are apart from the traditional wooden drums, also wooden drums divided into three sections (Y-section drums), which are said to have better results than the one chamber traditional drum.

    Specially for high quality leathers and relatively small quantities tanners often use stainless steel drums, called washing machines. A new development is the appearance of polypropylene (PPH) retanning and dyeing drums. The advantage of stainless steel and PPH retanning and dyeing drums is, that contrarily to wooden drums, these do not absorb dyestuff or keep remnants of dyestuff in the spaces between the fissures of the wooden beams. They can be thoroughly cleaned and they can be used for whatever colour. Wooden drums have dedicated drums for dark colours in which no light colours can or should be processed in order to avoid contamination.

    Stainless steel dyeing drums are in general smaller than wooden or PPH drums. Stainless steel drums must be heated and they are equipped with pumps that recycle the water/chemical bath through a a system of pipes and a heatexchanger. PPH drums can do what wooden drums can do. The same load, the same size, it also maintains like the wooden drum the temperature of the bath without outside intervention. The only significant processing difference between a wooden drum and a PPH drum is that from the maintenance point of view PPH drums are much easier and better to clean. PPH drums can be thoroughly cleaned, which for wooden drums is much more difficult. PPH drums can easily be repaired. Broken wood has to be replaced, a very costly operation, whereas polypropylene can be welded.

    1.5.2. Sammying and Setting out machine

    The sammying and setting machine is used after retanning and dyeing. The purpose is, after the leather has settled chemically for some 24 hours or so after the discharging from the drums, to squeeze out the excess of water and to spread the leather back to at least its original shape and size, taking out folds and thus gaining surface.

    Created by:LANCEY, Ms. Raphaelle 22/05/2007 3:53:36 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:47:05 PM

    MA. 1.6. - Drying Department

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    Drying leather is the final part of the wet stage in which chemicals are finally distributed over and throughout the leather and definitely fixed. The variety of drying methods is multiple from simple to very technological. The choice of the drying method depends on the type of finished leather the producers wishes to obtain. Each drying method has its own characteristics and provokes different effects on the finished leathers.

    1.6.1. Drying Tunnel

    One of a variety of methods and machines or equipment for drying leather is the drying tunnel. The drying tunnel is exactly what the word anticipates, a tunnel in which leather is hung from poles which rotate inside the tunnel and which are exposed to a steady flow of air generated by a ventilation system, whether heated or not, which decreases the surface humidity of the leather and results after a certain period of time in dry leather under controlled conditions.

    1.6.2. Drying Conveyor

    Another popular method for drying leather is the overhead drying chain. Leathers are being loaded on horizontal poles, which are attached to a conveyor, which on its turn is hung to the ceiling of a tannery (crust) department. Through motorisation the conveyor moves at a pre-established speed which allows the leather to dry within a pre-determined period of time. Leather is loaded at a loading station and unloaded at the unloading station which are one next to the other. The operation is little labour intensive. Drying can be naturally by the air in which the conveyor moves, or by running the conveyor through a drying chamber with ventilation and heating. The dimension of a conveyor depends on the production requirements of a tannery, the relative air humidity in the geographical area, and the temperature of the air.

    1.6.3. Pasting machine

    Paste drying consists in covering a glass plate with a starch solution to which the wet leather is being applied at the grain side and spread with smoothed plastic blades for maximum adhesion to prevent shrinkage during drying. The glass plates are inserted into a drying tunnel with controlled temperature and humidity from its it exists dry with a predetermined humidity content. This method of drying is nowadays rarely used. After drying the glass plats must be cleaned of the paste and also the leathers must be washed in order to assure proper penetration of the finishing chemicals.

    1.6.4. Vacuum dryer

    Vacuum drying is a fast method of drying leather in a strictly controlled way, which however requires a lot of energy. Vacuum dryers are generally constructed as a number of stainless steel tables, one above the other, where each table is both a working table and the closing table for the underneath lying table. The leather is spread onto the stainless steel table without additives. Tables can feature a temperature as low as 20 °C up to 70 °C. Once the leather is spread on the drying table, the closing table will be settle on top of the leather  and a vacuum will be pumped. Once the predetermined drying time is finished the vacuum will be neutralised to atmospheric pressure, the tables will detach one from the other and the leather can be taken off at the exactly right humidity as required by the processing formula.The number of drying tables can vary from merely one to up to 6 or seven if one above the other, or two tables, if adjacent. Although manufacturers tend to standardize the size of the drying tables, they can be custom made as well.

    1.6.5. Toggling machine

    Toggling machines combine a mechanical action with a drying action. Leather is placed horizontally on perforated tables and attached and being well stretched and held in place by toggles . The table is then turned 90 degrees into a vertical position. This turning action also mechanically moves the tables, which are horizontally divided in two parts, sideways increasing the tension of the leathers and hence increasing the surface. The tables are introduced, like books into on the shelves of  a book case, into a drying tunnel in which temperature and airflow are carefully controlled.

    Once inside the tunnel the tables are moved one parallel to the other to an exit point where the leather comes out dry at the required degree of humidity. The table is turned back in the horizontal position and the leather can be unloaded.A variation of the book type toggling machine is the automatic toggle dryer which works on exactly the same principle, but instead of frames sliding vertically into a sort of book case, the frames remain horizontal and form a conveyer. The extension action is obtained by running the frames over large wheels at either side of the machine.

    Created by:LANCEY, Ms. Raphaelle 22/05/2007 5:14:57 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:47:21 PM

    MA. 1.7. - Finishing Department

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    This is the last stage before the leather can be shipped out to the leather goods manufacturers. In this stage the leather is mainly cosmetically transformed.

    1.7.1. Conditioning machine

    After drying leather is usually stocked for some time before its turn in the finishing department. Since for finishing the humidity of the leather must be controlled, the leather must be reconditioned to ideal characteristics in terms of humidity. This can mean either increasing or reducing the humidity. In order to create the correct conditions one uses the Conditioning machine. Modern conditioning machines create an airflow in which water is vaporised both from the grain side and the flesh side of the leather in order to obtain the correct humidity throughout the whole section of the leathers. Simpler systems spray vaporised water on the grain side.

    1.7.2. Staking Machine

    Drying makes leather rather rigid, and the fibres of the leather need to be opened in order to obtain the correct softness before finishing. At the same time the fibres will be opened in order to provide for a correct penetration and anchoring of the finishing chemicals. To that purpose the leather is staked, which is a pure mechanical action. There are three main types of staking machines. The vertical staking machine which is suitable for soft garment leathers, the traditional arm staking machine, and the less labour intensive and highly productive through-feed staking machine. The action of all three machines is in principle the same. The leather undergoes a mechanical action both radial and transversal in relation to the surface of the leather.

    1.7.3. Shaving machine

    The purpose of the shaving machine is to bring pre-processed hides and skins (either vegetable or wetblue tannage) to the required and uniform thickness as required by the specifications of the finished leathers. Hides and skins are shaved at the flesh side by shaving blades which are fixed on a fast rotating cylinder. The leather is pushed by hydraulic pressure against the shaving blades which are in general electronically calibrated for the required thickness. Shaving can be done also when the leather is in dry condition.

    1.7.4. Dry splitting machine

    Hides and splits can be separated at three stages: in the lime, in wetblue and in crust. Each of these operations are executed by a splitting machine which are in principle one and the same machine, but adapted to the environment in which they operate. Lime splitting and wetblue splitting are executed in corrosive environments and have therefore suitable hardware, whereas crust splitting is non-corrosive but more delicate. Not only hides are split in dry condition, but also skins. The grain of goat and sheep are called skivers.

    1.7.5. Dry milling drum

    Dry milling drums come in wood, stainless steel and polypropylene. They run normally at a relatively high speed. No water is used, hence the word dry-milling. This drum does not perform a chemical tanning process, but effects exclusively a mechanical action that dramatically loosens the fibre structure of the leather with a very specific effect on the grain, which shows a pronounced and typical pattern. Dry-milling drums generate also heat as the leather is moved by a high number of revolutions with great friction which is not absorbed by a water bath. Moving smaller quantities and far lighter weights, drymilling drums are normally lighter in structure compared with drums that operate in other departments. For that reason dry milling drums don't require solid foundations like drums that require water baths.

    1.7.6. Buffing machine

    The buffing machine actually removes by means of a high speed roller that is covered with emery (buffing) paper and which acts against either the grain or the flesh side of leather, be that hide, skin or split, a very thin layer of the treated surface. In case of treatment of the flesh side or split the operation practically cuts the surface fibres creating a pleasant nap. The nap can be merely created for a pleasant visual effect, or in case of suede leathers to give the leather a finishing touch that determines the quality of the suede. Grain buffing I usually done in order to remove surface defects like scars. The buffing operation creates buffing dust which is removed from the leather by either dedusting brushes and/or an aspiration devise. Therefore a buffing machines is normally sold in the form of a buffing-dedusting line.

    1.7.7. Roll coating machine

    The roll coating machine applies a film of pigment to the leather that is run through the machine in a precise and controlled way. The roll coating machine is an evolution of hand padding and machine padding. There are two types of machine. The Reverse roll coater and the Syncro roll coater. The difference is fundamental.

    In the syncro roll coater the feed roller and coat roller turn in opposite directions at the same speed, which allows for a relatively small application of pigment at a time, but additionally allows for a pattern to be applied to the leather, like in a printing press, and use different colours.

    The reverse roll coater has the feed roller and the coating roller turn in the same direction allowing for a relatively heavy load of pigment to be applied by increasing the difference in the speed between the feed roller and the coat roller.

    Leather run through the roll coater has a high surface humidity and for that reason roll coaters are generally coupled to a drying tunnel, that allows the leather to be quickly dried for further treatment.

    1.7.8. Spraying machine

    The last finishing touch by application of chemicals to the surface of the leather is done by spraying the required chemical to the surface of the leather. The chemical can be aniline, pigment and/or fixing chemicals to assure consistent quality. The spraying can be done by hand or by machine. It is obvious that spraying by machine assures better quality consistency and higher productivity.

    The spraying machine consists of a long conveyer belt formed by a made of a number of nylon strings, that runs through a spraying booth and through a drying tunnel. The belt allows at the beginning for a loading station where the leather can be put on the belt and at the end a discharge station where the leather is taken off the belt either by hand or by machine.

    The spraying booth is equipped with a series of moving spraying guns, which can be moved by a mechanical arm or by a rotating carousel  which can be either circular or oval. The number of spraying guns can vary from 4 to 16 or more. The leather is run through the spraying booth at a determined speed and by regulating the speed difference between moving spraying guns and the conveyer one can increase or reduce he quantity of chemical application to the leather. Spraying booths are normally equipped with photo-electrical cells that can communicate with the spraying guns and determine where to action the liquid flow through the guns and where not, in order to spray only where leather is actually passing through the booth in order to save chemicals. After being run through the spraying booth the leather passes through a drying tunnel which generates a flow of warm air in order to dry the leather. Drying tunnels come in a large variety with simple heating solution like steam, gas or electricity or more sophisticated infra red systems.Most tanneries feature two cabin spraying machines, which are practically two spraying machines one attached to the other to double productivity.

    1.7.9. Embossing / Priniting press

    Depending on the requirements of the finished leather and depending on the surface defects shown on the grain, leather can be printed with a new pattern. The pattern can be a replica of a specific type of grain or any fantasy pattern. In order to do that you need to permanently alter the original grain with a new pattern. This can be done with the printing press, which can be either of the traditional plate type or of the continuous feed-through type. Huge pressure is exercised from 450 to 1'000/+ tons per square centimetre. The plate type press allows for a large number of patterns to be available at a relatively cheap price.


    A printing plate can cost somewhere between $3'000 to 10'000 depending on the complexity of the design. Films can be ironed onto the leather with special designs and patters. Feed through continuous presses use printing rollers, which are less easy to switch and far more expensive to construct. Therefore the continuous presses feature normally more than one roller which can be switched through a rotating mechanism, but the number of rollers is very limited compared to the infinite number of pressing plates that can be fitted on the traditional press. Continuous presses allow for high standard productivity whereas the traditional printing press has a relatively low productivity, but high flexibility for its output.

    Both types of presses feature smooth plates or rollers, which iron the leather and gives it a brilliancy or shine. Both presses need heat to warm the rollers or plates in order to be efficient. The method of heating can be electricity or steam.Sole leather is pressed with a different type of press. In order to obtain the typical finish of sole leather tanners use a roll press. A cylinder rolls alternative from left to right over sole leather under heavy pressure.

    1.7.10. Polishing machine

    The polishing machine which is a typical mono-bloc machine that pushes the leather with a transport roller against a polishing roller, which can be an amber-roller,  a cloth roller or a heated chromium roller. The operation is simple and clear cut and has the purpose to give the finished leather a specific look and feel while stretching also the surface and distributing the emulsified greasing agents inside the leather.

    1.7.11. Glazing  machine

    One of various methods to obtain brilliancy on finished leather is by means of mechanically rubbing a glass cylinder against the grain side of the leather. The machine that effects this operation is the glazing machine. A mechanical or hydraulic arm that holds a glass cylinder moves forward to position itself above the leather and closes on the leather in the backward movement. The friction between the glass cylinder and the leather  provides for the shining effect. The longitudinal centre of the glass cylinder is perpendicular to the forward and backward movement of the cylinder.

    1.7.12. Measuring machine

    Finished leather is sold per surface measurement unit, DM2 or FT2. The measurement can be done by hand, by mechanical measurement (pinwheel machine) or by electronic measurement. Since electronic measurement is nowadays practically the only used method, this paragraph will deal only with this method. Leather is being led through a barrier of photo-electric sensors at a determined speed allowing a computing device to calculate the exact surface of the leather. Measuring machines come with a number of options that allow for instance the machine to print on the leather itself the calculated surface. The measurement machine can be connected to a calculator that adds up the number of leathers composing a bundle and their single and total surface, up to composing a full packing list and invoice and to keep a whole stock position of a warehouse.

    Created by:LANCEY, Ms. Raphaelle 22/05/2007 5:41:17 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:47:38 PM

    MA. 1.8. - Process Control

    Contributed by: Mr. Arbeid, Ralph
    International Consultant, Arcapelli

    One of the most important features in the tanning industry like in all other industries is consistent quality. Hence quality control is extremely important. Until the large scale introduction of  computerisation in our lives, process control consisted of tanners being extremely capable and extremely careful when applying formulas. Checks are to be made frequently at large variety of stages during the chemical and mechanical processes.

    In order to assure consistent quality of mechanical operations, machine maintenance and of course quality awareness of workers are the key factors. Advanced technologies in the construction of machines and equipment in general have greatly contributed in achieving better and more consistent quality.

    Water is the main ingredient in tanning process formulas, and the management of water has until recently been ignored as an important contribution to quality control. Like any other chemical in the technological process, water must added in the right quantity and at the right temperature. Too much water means that the other chemicals are diluted excessively, whereas too little water means that the bath is too much concentrated. Either of these imprecisions during any of the processing stages affect the final quality of the leather. Water can be manually controlled with simple devices with a small investment, but at the same time with results, that are not precise.

    With the contribution of electro-mechanics first and electronics now, water management has become an easy, affordable and above all necessary factor in the  tanning process. Proper water management assists for better leather quality, saving of water and saving on effluent treatment, making this kind of equipment as much necessary as any other machine in a tannery.  Water management is only a first step on the road to full process and quality control. Chemical feeding and dosing can be introduced either semi or fully o automatic for both liquid and powder chemicals. Aniline preparation can be managed by computer assuring colour consistency, avoiding or reducing the necessity to correct colours during or after dyeing.

    Computers are now available to execute formulas and can direct the actual operations in a tannery. Drums can be run, stopped, reversed. If properly equipped drums can be drained and discharged by computer. Chemicals can be added and chemical tests like pH checks can be automated, although at a very high expense. Contemporarily or alternatively the computer can manage staff by calling for the preparation of chemicals and their adding to a tanning bath in the right proportion and at the right time. All these are factors that contribute and add to the consistence of quality.

    Created by:LANCEY, Ms. Raphaelle 23/05/2007 5:25:05 PM
    Modified by:LANCEY, Ms. Raphaelle 25/05/2007 4:47:52 PM


    TA.1.1. - Environment

    Using natural gas to supply energy using co-generation - January/February 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 10:17:20 AM

    This paper was presented as a poster by Mariliz Guttierres, department of chemical engineering, Rio Grande do Sul Federal University, Brazil, at the IULTCS biennial congress in Cancun, Mexico, May 2003. The authors were awarded best poster presentation by the panel of judges at the congress. The authors were M Gutierres; P S Schneider; H A Vielmo; N R Marcílio; R Danieli; S T Conceição, Rio Grande do Sul Federal University. The full paper is presented in Spanish in the proceedings of the IULTCS Cancun congress.


    From the energy point of view, transformation processes found in tanneries need heat for hot baths in drums, to dry leather and to warm up the machinery.
    In general, steam is used at different levels of temperature, as well as electrical power, in machines, engines and other services.

    The co-generation technique consists of generating electrical and thermal power starting from the same combustible material.

    Use of co-generation systems enables an efficienct increase in the generation system.

    Although its use might seem obvious, it is only justified when conditions of guaranteed demand from generated heat produced by the combustion of the energetic components are calculated.

    The objective of this work is to develop methodologies to allow decision making and assess the viability of introducing a co-generation system using natural gas in tanneries.

    Energy data was taken from a representative number of tanneries located in the State of Rio Grande do Sul, Brazil.

    Data collection from the companies included their work systems, leather production, consumption and power of electricity, fuel consumption and steam generator production.

    A co-generation system case study was carried out in a tannery processing wet-blue hides, using simulation software packages.

    The methodology is based on the efficiency of transformation processes in tanneries in terms of their thermal demand.

    In addition to the possibility of implementing a system that could make the industry more competitive, the objective was to identify an industrial sub-sector with potential uses of natural gas.


    The word co-generation has a technological origin which designates a specific type of thermal system where there is a combined generation of two different types of energy sourced from the same combustible material.

    Also, this term is particularly used to represent the generation of electrical power (or mechanical) and thermal power from the same combustible material.

    The use of co-generation facilities is a well known practice around the world and there are several success stories in different countries.

    The use of these systems is also frequent in Brazil, where the generation of thermal and electrical power in the sugar-alcohol, petrochemical, iron and steel and other industries is particularly outstanding.

    Today, with the availability of natural gas, we observe that co-generation modifies the power supply of different industries and commercial facilities, including the ones set up in regions of high urban mass, allowing a smaller environmental impact than other combustible energy sources.

    Natural gas originates from the degradation or breaking down of the organic material which undergoes high temperatures and pressures, or has been attacked by anaerobic bacteria millions of years ago.

    Gas can be related (or not) to petrol. In the second case, the extraction cost is much lower.

    Natural gas is a mixture of gases which includes some hydrocarbons, mainly methane and ethane. There is an abundant content of methane in the mixture.

    Natural gas composition is not uniform, as it varies depending on the deposit of origin, which influences its properties. As an example, Table 1 shows the approximate composition of natural gas distributed in the State of Rio Grande do Sul.

    According to Teixera (2001), in regards to his comments about the combined generation of electricity and heat, both configurations, normally used in the setting up of a co-generation unit, according to the energy characteristics of the enterprise are: 'topping' or superior cycle and 'bottoming' or inferior cycle. Designs of both configurations from Danieli (2002) are shown in Figures 1 and 2.

    In the 'topping' configuration or superior cycle, some combustible material is burnt in a turbine or in an internal combustion engine to generate electricity, where the heat delivered is used in other processes.

    In the 'bottoming' configuration or inferior cycle, some combustible material (for example natural gas) is burnt in a boiler to generate steam.

    A steam turbine adjusted to an electric generator is activated by the steam delivered, and responds to a company's electricity power demand. When only one part of the generated steam in the boiler is used by the turbine, the other part is used in other processes in the company requiring high pressure steam.

    The steam that passed through the turbine, delivering to the axis part of the energy, can also be used in industrial processes that require steam at medium and low pressures.

    According to Paterman (2001), in principle co-generation applies to any facility in which both electrical and thermal power is required.

    Thermal demand can include direct heat (discharge gases), steam, hot water, hot oil and refrigeration. The latter can be obtained through electrical power, which in this case leads to electrical demand.

    Co-generation recovers the refrigerated system via absorption, which generates cold water from heat, but used in places where there is no electricity.

    Setting up a co-generation system requires a substantial change in the considered consumer's profile. This means going from being a buyer of electrical power to being a seller, and consumer, of a combustible material such as natural gas.

    Viability studies of energy systems begin with the technical aspects, where data about the company or facility's consumption profile is taken. Their objective is to determine a constructive determination of the system and its dimensions.

    The economic analysis is an important task in the context of co-generation. It consists of checking if the set up of a co-generation system is capable of bringing economic benefits, comparing it to the referred or actual configuration.

    In other words, that analysis compares the existing project or the potential one in the conventional mode with the one that could be a co-generation plant, and bearing in mind the demands from the processes involved, evaluates the return on the investment.

    The technical-economical viability study is complemented by the financial analysis. After finding out what would probably be the annual benefit that could be obtained with the co-generation system (obtained through the economic analysis), it evaluates the benefit's capacity of covering the investment and the ordinary costs of the new plant.

    As mentioned before, the use of co-generation systems is reasonably known and the effort made in this study was to describe in detail the methodology used in the case of tanneries.

    The paper presented is part of the activities performed in a project about 'Natural Gas Co-generation in Tanneries' (Schneider and collab, 2001).

    Some of the results are described with regard to the energy profile in tanneries and a case study in a tannery is cited, from which real operation data will be used to simulate co-generation systems.

    Energetic characterisation in tanneries

    Data was collected to evaluate the energy consumption in tanneries located in Rio Grande do Sul, from visits to a few selected facilities. The State has 126 tanneries registered under the Brazilian Association of Chemists and Leather Technicians (2001).

    A few tanneries were visited and placed into three categories as follows: Tannery type A (including all processes beamhouse, tanning, retanning and finishing), type B (beamhouse and tanning) and type C (retanning and finishing only).

    The tanneries were selected following the criteria of proximity to the natural gas distribution line, whether in existence or projected. This information was submitted by SULGAS, which supplied maps of their distribution lines.

    The tanneries visited consume electrical and thermal energy. Electrical power is mainly used in engine activation, followed by lighting in the facilities and a small portion for offices and other general uses. Thermal energy is used to heat water and solution used for leather treatment, leather drying and machinery heating.

    In some cases, the steam is directly injected in the process, for instance when staking leather during the pre-finishing and finishing operations (tanneries type A and C).

    Figure 3 shows the configuration found in all the visited cases. The superior line (electrical network) refers to the supply of electrical power, sourced from the licensed provider, or from moto-generator groups, existent in most cases and operating in peak hours.

    Thermal energy is produced in generators of saturated steam (evaporator or boiler on the diagram). The steam can be directly distributed for the process or used to heat up the liquid water in the heaters.

    A survey to collect energy data was performed in each visit. The main items in each questionnaire were as follows:

    •  Name of the tannery

    • Electrical power: electrical consumption, auto production (generator groups), electricity bill, demand profile

    • Thermal energy: types of energy ingredients, boiler operation system, fuel bill, demand profile

    • Product classification: classification of leather produced, product distribution in regards to the total production

    Evaluation procedures were performed to calculate the consumption and power data of the tanneries visited, separated by type of component.

    Electrical power data were identified immediately (ref. 1), as the power providers supply bills in kWh, and highest power demanded, in kW. Both data refer to periods known as 'peak hour' (from 18.00 to 21.00 hours) and 'off-peak' (rest of the period).

    Besides, all electricity bills showed historic consumption for the previous 12 months, for both tariff periods, which enables us to determine the monthly value consumption on an annual average.

    The profile for daily energy demand was facilitated by the tannery owners and it is basically the sum of the energy purchased from the utility supplier and the one generated in the generator groups (auto-production).

    The power supplied by auto-production was calculated using the thermal energy generated due to the consumption of diesel oil on the moto-generators, associated to its efficiency.

    Most of the tanneries have energy generator groups, based on diesel engines, which characterises auto-production, and these operate at peak times. The consumption in that period is usually constant.

    The facilities vary in the following cases:

    • Auto-production with power from the generator groups incapable of supplying the whole electrical production, forcing a reduction in production

    •  Auto-production with enough power from the generator groups to supply electrical production

    •  Auto-production installed but extra hours of work are carried over to the next day, avoiding self generation or purchase of energy at peak times

    •  Without auto-production, purchase of energy at peak hours. In these cases, the amount of energy at peak time exceeds the one at the normal period.

    In all cases with auto-production, no co-generation installation was found. During the off-peak time, the consumption profile was facilitated by the area managers in each company, following the same pattern: constant demand during the day, with a light reduction over lunch times in some cases.

    Unlike the previous case, thermal energy needs to be estimated since no company had power meters (instant measurement) or consumption meters (integrated measurement) enabling power quantification.

    All tanneries have boilers, generating saturated steam. Consumption evaluation was performed associating steam production to a demand profile.

    Thermal energy demand was estimated using data of combustible consumption (wood) over a one month period.

    However, there were doubts about the process efficiency, which includes generation in the boilers and steam distribution, and also the fact that the wood bills supplied do not correspond exactly with the consumption period.

    Therefore, we have not reported this data here.

    We opted for the thermal energy data obtained through steam production. This alternative is calculated using operational data from the boilers, taking into account the flow and the pressure produced.

    Energy calculations were made and the results given in Table 2.

    The evaluation through steam production presents other uncertainties, as it assumes the boilers nominal values (pressure and flow of saturated steam), which are supposed as constant during a day's work.

    The summary of data obtained through nine tanneries is presented in Table 2.

    The production index by energy consumption IE was defined. With the data from the previous table and from leather production, the indexes in Table 3 were obtained.

    IE = P/E

    Where, IE: production index by energy consumed [m2/MWh]

    P: monthly leather production [m2]

    E: energy consumed [MWh] over a month period of 22 working days

    The visit to the tanneries enabled us to check that all have the same energy standard. The table shows that the electrical energy always represents less than half the total demand of the tannery. This leaves around 20% of the energy wasted for the tanneries visited.

    The thermal section represents the remaining 80% of energy consumed, but it is important to highlight that there is a waste of energy, checked in all the facilities visited. The waste is attributed to two causes:

    • One is due to isolation faults, loss of steam in the pipes, leaks etc, which can be reduced with a good maintenance programme and small investments. This section of the waste is not the most important.

    • The other is the excessive generation of steam once steam is required in some processes but does not require distribution throughout the whole tannery. There are cases where heat is used just to warm up baths to less than 60ºC, and this steam is generated, transported and then condensed, resulting in a reduction of energy efficiency in the facility. This section of the waste is the most important.

    The latter observation can be very useful in the dimension of the co-generation equipment. The demand of thermal energy for baths can be supplied directly by the warmed up water via the engine cooling system, without the need to generate steam in the recovery boiler. This will represent a lower amount of heat than the current one consumed in the tanneries.

    It also important to highlight that the co-generation facilities are measured to meet the electrical needs (electrical parity project) or thermal needs (thermal parity project).

    On the electrical parity project, the equipment is measured to meet the electrical demand in the facility.

    The thermal energy section required to supply the processes can be either added, as a supplementary heater in the boiler, or result as excess, which can then be exported to other facilities close by.

    On the thermal parity project, the initial objective is to meet the thermal needs and the electrical section can be purchased by the utility provider or sold to the distribution network, according to the result of the energy balance.

    Analysis of a case study

    A tannery was selected for an energy analysis. The tannery production line is quite similar to most companies in the region. This enables the use of the obtained results in this paper to project co-generation systems. The tannery's main raw materials are wet-blue hides and it processes leather in the retanning (neutralisation, retanning, dyeing and fatliquoring) and finishing departments (tannery type C).

    The production process requires a large number of machines. Electricity is consumed mainly in electrical engines activating pumps, air compressors and machinery in general. Thermal energy is necessary in several stages of leather processing.

    During the peak-time in the tannery (from 18 to 21 hours), electrical energy is produced by a diesel generator and during the remaining time (off peak) it is purchased from the utility provider.

    Thermal energy demand is supplied by burning eucalyptus wood in a boiler ATA 17LC, producing saturated steam with 6kgf/cm2 pressure. Most of the steam generated is used in heat interchangers to dry the leather. The rest is used to warm up the water.

    In order to perform a numerical simulation of a co-generation system applied to this company, energy data was collected.

    The access to the data of electrical energy consumption and to the monthly bill, had been possible using the 'mass memory' data supplied by the utility company.

    In other words, for high voltage consumers, the utility provider measures (every 15 minutes) the power demanded by the company.

    With regard to thermal energy required by the company, a survey was carried out over 15 days to measure the flow, pressure and water temperature when feeding the boiler.

    This is when the water returning condensed is injected for vapourisation.

    Data was taken every 15 minutes in order to obtain a satisfactory resolution from the operation system. Knowing the status at this point and knowing that the boiler produces saturated steam at a known pressure, data was obtained to quantify the energy demanded. Data registered during the measurements are presented in Table 4.

    Software simulation of co-generation systems

    Four systems were used. The full procedure is given in IULTCS proceedings from Cancun.


    Data collected during the visits provided a general overview of the energy distribution in the tanneries.

    It also contributed to the formulation of an analysis methodology, valid for viability analysis of co-generation systems. The following pattern concerning the use of energy in tanneries was identified:

    • Need for steam to be used directly in operations with leather or indirectly by mixing it with water from the network or recycling from any tannery process, thus making available hot water from the process. Generation of saturated steam is often found in the pressure gauge of approximated 6 to 7 atm and, therefore, the temperature is 165° to 171°C

    • The energy source extensively used is wood, acacia in most cases. Eucalyptus and other wood waste sourced from furniture industries are also used

    • Electrical power is purchased from the public network and self-generated, in the peak time, from 18 to 21 hours

    • Data collected regarding energy demand reveals a potential use of co-generation systems in tanneries, formed by the following observations:

    Thermal energy demanded is maintained in a proportion of 2:1 with the electrical demand, which enables an installation based on the thermal parity.

    During many stages of the production line, the use of liquid water is an alternative energy source without the need of generating steam.

    This aspect of the process can be useful if the cooling water for the engines of the co-generation system is used.

    The different co-generation systems simulated seemed very efficient, given that during co-generation a type of energy that is normally wasted, such as heat, is recovered.

    Although not being an energy as efficient as electricity, from a thermodynamic point of view, it can still add up to the useful energy in the system.


    The authors would like to acknowledge the financial supporters of this project.

    They include: A RedeGasEnergia, which is formed by the following companies: Petrobras, TBG, Sulgas and Finep. Also, Curtiembre Natur for the use of their facilities and information for the case study, especially Marcelo Luis de Almeida Sartor.

    Finally, all the other tanneries where energy data was collected.

    Mariliz Guttierres, department of chemical engineering, Rio Grande do Sul Federal University, Brazil presenting a paper at the IULTCS congress in Cancun, Mexico.


    1. P Abreu and J Martinez. 'Gas natural, o combustível do novo milênio', Plural Comunicação, Porto Alegre, 1999

    2. F N Teixera. 'Co-geração e Geração Distribuída', Petrobrás Distribuidora S/A, Rio de Janeiro, 2001

    3. R Danieli. 'Trabalho de Diplomação do Curso de Engenharia Mecânica', Universidade Federal do Rio Grande do Sul, Porto Alegre, 2002

    4. Paterman, 2001. Utilizações do Gas Natural - II, Co-Geração. 'Curso de Especialização em Utilizações do Gas natural'. Programa de Pós-Graduação em Engenharia Mecânica, Universidade Rio Grande do Sul, Porto Alegre, 2001

    5. P Schneider, H A Vielmo, M Gutterres, N R Marcílio, R Danieli, S T Conceição. 'Co-geração a Gas Natural em Curtumes', Projeto FAURGS/FINEP 21.01.0456.00 CTPetro, Porto Alegre, 2001

    6. Associação Brasileira dos Químicos e Técnicos da Indústria de Couro (ABQTIC) 'Guía Brasileiro do Couro', Estância Velha, 2001

    7. Sulgás - Companhia de Gás do Estado do Rio Grande do Sul

    8. Sim Tech 2000. 'IPSEpro Process Simulator'

    Created by:LANCEY, Ms. Raphaelle 30/10/2007 3:21:14 PM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 10:17:20 AM

    New methods for stabilising wet-blue shavings - April 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 11:54:56 AM

    Percolation trials have also been carried out to assess the level of chrome separation from the shavings. The results from the lixiviation trials were satisfactory with a reduction of chrome leaching that can exceed 99.9%. These trials were carried out at the CTC laboratories, Lyon, France.

    Wet-blue shavings are leather flakes which are chrome tanned and are generated through the shaving process. The material has not been neutralised, dyed, fatliquored or finished. From preliminary studies about waste deposited by the leather industry it has been shown that shavings have a tendency to leach chrome.

    In the European Union, shavings are classified as non hazardous waste. They are, therefore, admitted in non hazardous waste landfill. The trials described in this study have been carried out on a prevention basis in order to reduce chrome leachates. The criteria for admission in hazardous waste will be taken as a reference.

    The purpose of this project is to stabilise the shavings so as to decrease the release of chrome during leaching. Furthermore, as European regulations refer equally to percolation, it has been decided to carry out the trials through percolation also.


    The capacity of a material (or waste) to release a substance into the environment is measured by lixiviation. The standard test consists of putting the material into water, stirring, filtering and analysing the concentration of the substance in water.

    The waste shavings should be taken from the wet-blue state with a grain thickness of 4mm. The shavings are consequently dried and then ground.

    A mass ratio liquid/solid of 10l/kg (calculated in equivalence of dry material) is necessary for the test.

    The demineralised water and the waste shavings were placed in a bottle and then stirred (16rpm/min) for 24 hours. The eluent is then separated through vacuum filtration at 45m and then analysed. The lixiviation or leaching test is carried out under norm NF X 31-210.


    The percolation trial aims to determine the release of elements from the waste shavings placed in a column where they are subject to a continuous upward flow of water.


    Looking at the potential-pH of chrome and the neutralisation process of leather after tanning, it was decided to neutralise the leather shavings by adding alkaline products. Three chemical products in powder form were selected: lime powder, sodium carbonate and bicarbonate.

    The dried waste was ground and the neutralisation salts or stabilisers were added. Brief stirring was carried out manually. The resulting mixture undergoes lixiviation.

    Analysis on different chemical parameters were carried out on the leachates including the amount of total chrome and chrome VI.

    Chemical analysis

    The picture above shows three samples obtained with different lime concentrations: the first has an absence of lime and is the control sample (O). Bottles Q and S both contain 2% and 2.5% of lime respectively. The blue colour in the control sample indicates the presence of chrome. This is confirmed by the analysis presented in Table 1.

    The addition of lime, sodium carbonate or bicarbonate reduces the chrome concentration in the water. The most interesting results were obtained with lime. The amount of lime added became less relevant, as the chrome content is lower in the final water. Additionally, the cost per kg of lime is lower than sodium carbonate and bicarbonate.

    However, COD, BOD5, chlorides, sulfates and the phenol index increase with the percentages of stabilisers added.

    The concentration remains, nevertheless, inferior to the limits established by the level of hazardous waste contained in discharges of non hazardous waste.

    On no account does this stabilisation generate any hexavalent chrome. The trial of the 5% lime offer shows that the doses added need to be precise. The amount of chrome identified in this sample is in fact higher than the one detected with lower quantities of lime.

    Adding 2% of lime to the bulk shavings helps the fixation of the chrome in the wet-blue shavings thus provides a 99.9% reduction of the total chrome contained in the eluent following the stabilisation treatment.

    Economic study and industrial implementation

    A simple mechanism has been considered to implement this process. The shavings should be transported on a conveyor belt into a skip. A tank containing lime in solution is installed above the conveyor belt. Lime pours out in a continuous flow onto the shavings along the conveyor. The conveyor, the tank and the hopper dispensing the lime liquor are all linked electronically to control the flow.

    The estimated investment cost for such a system which is a single motor unit with a dispenser including a 30 litre channel hopper and an additional 30 litre hopper is €6,000.

    Above: peristaltic pump and percolation column of shavings. The eluent collection bottle is in the foreground.

    Percolation test

    The percolation trial is aimed at identifying the release of elements issued from waste placed in a column where they are subjected to a continuous upward flow of water.

    Changes in disposal regulations have led to the idea that percolation could become a parameter for the admission of non hazardous waste. This percolation is described in a European pre-norm from March 2002: pr NF EN 14105. Following this norm, CTC decided to set up a percolation column in their laboratory and carry out comparative trials with the leaching tests.


    When carrying out the trial 'tests' on bulk shavings, the quantity of compacted waste in the column was very small. The ratio liquid/solid is 0.1l/kg. It follows that the volume of eluent taken is limited.

    By drying the waste, the amount collected was more acceptable. Therefore waste was then dried before being compressed into the column.

    Eluent analysis

    The results are shown in Table 2. The European admission criteria of hazardous waste for the dumping of non hazardous waste are used as a reference (2.5mg/l for total chrome in percolation). Thus with 85mg/l of chrome in the percolate, the bulk shavings do not meet this limit.

    On the other hand, the shavings stabilised with lime did meet the limits (0.8mg/l versus 2.5mg/l). The reduction in total chrome content in the percolate was 99%. These results follow the same pattern as the ones obtained in the lixiviation trials.

    With regards to COD and chlorides, the concentration after percolation is higher in the stabilised shavings than in the bulk shavings. The limit for admission of hazardous waste in CET of non hazardous waste is also within the set limits. There is no limit proposed for COD.

    Concerning the sludge trials, the concentration of total chrome is superior to the acceptance limit of hazardous waste in CET of non hazardous waste.

    These trials made it possible to check the stabilisation of shavings via another method by adding 2% of slaked lime. Stabilisation of the wet-blue shavings leads to a 99% reduction in chrome content leached into the eluent.

    Finally, it has been possible to compare the results obtained in the lixiviation and percolation eluents. Percolation eluents are more concentrated than the ones using the lixiviation method.

    Limits of acceptance of hazardous waste in CET class 2 are also higher for those percolates when compared with the leachates.



    By adding 2% lime to stabilise the bulk mass of the wet-blue shavings, this can result in a 99% reduction in the leaching of chromium. This is according to the NF X 31-210 standard.


    Investigations carried out on the percolation of waste have enabled the establishment of an upward flow column at CTC's laboratory in France. As this is operational, lab technicians are able to carry out percolation trials on waste wet-blue shavings or any types of waste.

    The set up of the column has enabled trials to be carried out on bulk shavings and 'stabilised' shavings. The results obtained confirm chrome stabilisation in the shavings with the addition of lime. Stabilisation leads to a 99.1% reduction in the chrome content of the eluent.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 11:54:56 AM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 11:54:56 AM

    Cleaning wastewater by phytoremediation - May 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 12:01:33 PM


    Phytoremediation combines the Greek word 'phyton' (plant), with the Latin word 'remediare' (to remedy) to describe a system whereby certain plants, working together with soil organisms, can transform contaminants into harmless and, sometimes, valuable forms. This practice is increasingly used to remediate sites contaminated with heavy metals and toxic organic compounds.

    Whilst the technology has historically been applied to soil clean-up, it can also be applied to the treatment of tannery waste. This article provides an overview of the technique, together with information concerning the specific application to the leather industry (ie the use of reed beds).

    Phytoremediation uses green plants to rid soils and wastewater of toxic heavy metals and metalloids. It can be defined as the clean-up of pollutants primarily mediated by photosynthetic plants.

    These plants and their microbially-active rhizosphere (root zone of influence) can transform pollutants and the nutrient nitrogen into valuable biomass, with the remaining water removed via evaporation and transpiration.

    The range of biological treatments for environmental problems, as described by the term phytoremediation, actually consists of several specific processes:

    * Phytoextraction - Uptake of substances from the environment, with storage in the plant (phytoaccumulation)

    * Phytostabilisation - Reducing the movement or transfer of substances in the environment. For example, limiting the leaching of substances contaminating soil

    * Phytostimulation - Enhancement of microbial activity for the degradation of contaminants, typically around plant roots

    * Phytotransformation - Uptake of substances from the environment, with degradation occurring within the plant (phytodegradation)

    * Phytovolatilisation - Removal of substances from the soil or water with release into the air, possibly after degradation

    * Rhizofiltration - The removal of toxic metals from groundwater

    Phytoremediation takes advantage of the nutrient utilisation processes of the plant to take in water and nutrients through roots, transpire water through leaves, and act as a transformation system to metabolise organic compounds, such as oil and pesticides. Alternatively they may absorb and bio-accumulate toxic trace elements, including heavy metals such as lead, cadmium and selenium. Heavy metals are closely related to the elements plants use for growth.

    Phytoremediation is an affordable technology that is most useful when contaminants are within the root zone of the plants (top three to six feet of the soil). For sites with contamination spread over a large area, phytoremediation may be the only economically feasible technology.

    Wetlands phytoremediation

    Wetlands are defined as land where the water level is near the ground surface long enough each year to maintain saturated soil conditions. Marshes, bogs and swamps are all examples of naturally occurring wetlands.

    A 'constructed' wetland is defined as a wetland specifically constructed for the purpose of pollution control and waste management.

    There are two types of constructed wetlands: the free surface wetland and the sub-surface flow wetland. Both types utilise aquatic vegetation and are similar in appearance to a marsh.

    For the purposes of phytoremediation, wetlands are shallow waters with at least 50% aerial cover of submerged of emergent macrophytes or attached algae.

    Natural wetlands have long been used for the disposal of waste. Any treatment occurring in early waste disposal wetland was incidental and confined to some reduction in the biological oxygen demand (BOD).

    Thus natural or constructed wetlands are best reserved for two purposes:

    * Polishing of already partially oxidised industrial or domestic waste

    * Removal of specific pollutants, such as nitrogen, phosphorus, copper, lead, organic compounds and pesticides from all wastes including agricultural or urban storm run-off

    These treatment wetlands utilise plant-based enzymatic biochemical processes, which work in conjunction with indigenous microbial activity to optimise rhizospheric biodegradation and plant tissue phytodegradation.


    Soil micro-organisms can degrade organic contaminants. This is called bioremediation and has been used for many years both as an in-situ process and in land farming operations with soil removed from sites.

    It has been demonstrated, for example, that certain varieties of mustard plant can remove metals such as chromium, lead, cadmium and zinc from contaminated soil. Also hydroponic plant cultures have been used to remove toxic metals from aqueous waste streams.

    Plants can accelerate bioremediation in surface soils by their ability to stimulate soil micro-organisms through the release of nutrients from and the transport of oxygen to their roots. The rhizosphere is a zone of increased microbial activity and biomass at the root-soil interface that is under the influence of the plant roots.

    This zone of soil, being closely associated with the plant root, has much higher numbers of metabolically active micro-organisms than unplanted soil.

    It is this symbiotic relationship between soil microbes that is responsible for the accelerated degradation of soil contaminants.

    One of the more important roles of soil micro-organisms is the decomposition of organic residues with the release of plant nutrient elements such as carbon, nitrogen, potassium, phosphate and sulphur. A significant amount of the CO2 in the atmosphere is utilised for organic matter synthesis, primarily through photosynthesis. This transformation of carbon dioxide and the subsequent sequestering of the carbon as root biomass could reduce potential problems associated with global warming.

    Absorption of large amounts of nutrients by plants (and only a small amount of plant toxins that might be harmful to them) is the key factor for this technique to succeed. Plants generally absorb large amounts of elements they need for growth and only small amounts of toxic elements that could harm them.

    Economical aspects

    Phytoremediation is considered to be a cost-effective alternative to conventional remediation methods.

    Cleaning the top 15cm of contaminated soil by applying phytoremediation costs an estimated £1,500-8,000 per hectare, compared to £5,000-13,000 per hectare for on-site microbial remediation. If the soil is moved, the costs escalate, but phytoremediation costs are still far below those of traditional remediation methods, such as stripping the contaminants from the soil using physical, chemical or thermal processes.

    Plants are effective at remediation of soils contaminated with organic chemical wastes such as solvents, petrochemicals, wood preservatives, explosives and pesticides. The conventional technology for soil clean-up is to remove the soil and isolate it in a hazardous waste landfill or to incinerate it.

    Organic contaminants are in many cases completely destroyed (converted to CO2 and H2O), rather than simply immobilised or stored.

    Reed beds

    What is a reed bed?

    Reed beds are self-contained, artificially engineered, wetland ecosystems. In simple terms, a reed bed is a hole in the ground, lined with an impermeable liner, filled with one or more solid media (eg soil) and planted with a sufficiently robust reed species. The system is then fed effluent and drained by gravity.

    Reed beds can be built in a number of variants but mainly they are of the horizontal flow or down flow configuration. The two types can also be used in combination where necessary.

    Horizontal flow reed beds can be of the surface flow or sub-surface flow type. By far the most common type is the sub-surface flow which is often used for final polishing or tertiary treatment applications. Surface flow reed beds are often used for metals removal and settlement applications.

    Reed beds are a cost-effective method of sewage treatment. The systems are robust and well-proven, requiring only a fraction of the maintenance of traditional methods of treatment. Chemicals are not required and, provided that just over one metre of hydraulic head is available between the process and final discharge point for the treated effluent, no power is required.

    Sludge disposal has become a major waste treatment issue for producers. In the past, sludge, both in liquid and solid form, could be disposed of to landfill at reasonable cost. Recently, however, legislative measures have been instigated which make landfill an increasingly expensive and time-limited disposal option.

    Sludge treatment reed beds will fulfil the requirements of the 'safe sludge matrix', producing an 'enhanced treated product'. Furthermore, the bio solids produced are highly mineralised and dewatered to a dry solids content of some 40%.

    Reed beds are becoming increasingly popular for the treatment of both industrial and domestic effluents, offering a simple, robust and cost-effective means of wastewater treatment. Reed beds have been applied to the treatment of domestic effluents in rural communities, where the relatively small volumes of effluent may mean that conventional systems are not cost-effective.

    BLC is developing reed bed technology for leather effluent treatment in co-operation with the company ARM Ltd. Reed beds are a promising technology for the developing world, where high tech treatment is too expensive or impractical, but still aims to fulfil local discharge compliance. BLC can offer testing, implementation and start-up of large scale reed beds for industrial wastewater treatment.

    For further details contact Stuart Booth on stuart@blcleathertech.com or +44 1604 679956.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 12:01:33 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 12:01:33 PM

    New environmental service to the global leather industry - October 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 4:41:42 PM

    W2O Environment Ltd, a UK-based consultancy, offer independent environmental engineering, consulting and training for the leather industry worldwide. The company have ten years' experience in environmental technologies in the leather industry and offer a complete environmental assessment for tanneries, including the areas of leather processing and effluent treatment.

    Within the environmental audits, they examine factory operations, looking at critical areas of process control in the tannery and opportunities for cost reduction and/or for implementing cleaner technologies.

    They review the effluent treatment facilities regarding wastewater concentrations, flow rates, retention times and operation regime as well as odour control and sludge handling and implement monitoring and environmental quality systems ensuring consistent pollution control.

    The programme of W2O Environment consists of a comprehensive audit and gives technical assistance to current leather process and effluent treatment plant operations and serves as a basis to develop a strategy for future effluent treatment and waste management to meet international standards and local regulations.

    Following the initial auditing, they offer further support with design and layout of effluent treatment plants, upgrading and process design of novel and highly-efficient effluent treatment and water recycling plants.

    Key areas of activity include the development of novel recycling technologies using membrane bioreactor and nanofiltration/reverse osmosis technology to provide for high-quality water recycling.

    Prior to implementation, they test the recycling technologies with pilot plants at the tanneries to evaluate the technical feasibility and investment and operation costs, to obtain the design basis for industrial scale systems. On successful completion of the test, they assist during implementation, conduct commissioning and start-up of the plant and train the operators.

    W2O Environment Ltd are keen to support the leather industry with state-of-the-art cleaner and ecologically sound technologies and aim to reduce pollution and meet today's stringent consumer demands for quality and environmentally-friendly production.

    For further information, visit: [http://www.w2o.environment.net]

    Reverse osmosis plant for tannery effluent treatment and recycling with 5,000 m3 per day capacity

    Clean Tech and Environmental consulting for a wet-blue tannery in Namibia

    Clean Tech assessment of the beamhouse process in a Colombian tannery 

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 4:41:42 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 4:41:42 PM

    TA. 1.2. - Membranes

    Drinking water from tannery discharge - March 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 10:17:41 AM

    The tanning cluster around the town of Lorca in southern Spain is the location for the world's first Membrane Bioreactor and Reverse Osmosis treatment unit. The plant caters for a group of 25 tanneries and offers complete removal of salts and pollutants from tannery wastewater. Dr Wolfram Scholz, BLC Leather Technology Centre, discusses how drinking quality water may be obtained from tannery effluent using the new technology.

    BLC have just completed a landmark project to design and commission the world's first Membrane Bioreactor (MBR) and Reverse Osmosis (RO) treatment plant, which can process tannery effluent to desalination levels.
    The plant, based in Lorca, Spain, treats effluent from a group of 25 tanneries based in the region.

    The modern tannery wastewater treatment plant consists of basic chemical/physical treatment with catalytic oxidation of sulfide to sulfate and primary solids separation of the mixed tannery effluent. The subsequent secondary biological treatment removes high COD and BOD and suspended solids.

    However, salts such as sulfates and sodium chloride (found in tannery effluent in concentrations of SO4 >3g/l and NaCl >20g/l) cannot be eliminated with conventional treatment techniques and as such contribute significantly to the environmental impact. An unsolved problem up to now had been the persistence of salts in effluent as there has been no economically feasible treatment technique available.

    The presence of salts also complicates the overall intentions for recycling and re-use due to concentration effects. The industry has been urged to implement new treatment processes in order to cope with stringent environmental legislation and to reduce organic pollution, in particular the salt impact on surface waters.

    BLC has developed a combination of MBR and RO treatment, which enables efficient polishing of tannery effluent and complete elimination of salts. The application of such technologies allows complete water recycling of mixed tannery effluent as process water and water re-use for irrigation purposes.

    BLC in co-operation with AGBAR (Aguas de Barcelona) carried out a long-term pilot study, which was funded under a LIFE EC research project at Lorca, Spain, to realise the potential of large scale application of MBR and RO tannery wastewater treatment. Extensive experimental trials were performed over 14 months to determine the operating conditions for the Ultra filtration (UF) membrane filtration in respect of cross flow velocity and transmembranal pressure and to establish ideal hydraulic retention times (HRT) and sludge retention times (SRT) for the bioreactor to achieve optimal MBR process performance.

    Simultaneously, the RO pilot plant was tested with MBR permeate at various pressures and recovery rates to obtain the required optimum design parameters. The results provided an outline design for the construction of a full-scale MBR and RO plant with 5,000m3/day treatment capacity for mixed tannery effluent from 25 local tanneries.

    The construction of the wastewater treatment plant was completed in June 2003 and is currently operated by Aquagest Levante. The wastewater treatment plant is part of a co-generation concept in which electricity is generated on-site in a gas power plant which also provides heat for the effluent treatment plant (Figure 1).

    Figure 1: Cogeneration plant in Lorca Spain. Courtesy of Aquagest

    MBR and RO operation

    The mixed effluent are collected and filtered through a rotating screen to remove gross solids, hair and fibres prior to being pumped to the effluent treatment plant.

    Initially sand, earth and fats are removed in a trap, following a balancing step in a 4,000m3 holding tank. Pure oxygen is introduced via a venturi aeration system to guarantee sufficient sulfide oxidation and mixing.

    The effluent are continuously transferred to a primary treatment plant, where specific coagulation and flocculation systems are applied.

    The primary sludge is settled in a lamella separator and dehydrated with centrifuges and further dried in a tunnel sludge drier, which is operated with the off-heat from the gas power station. After primary treatment the effluent are screened to remove residual hair and fibres and 230m3/hr is fed into the bioreactor.

    The bioreactor tank is operated at 8,000-10,000mg/l MLSS with a retention time of 19 hrs. Aeration and mixing is provided by a Jetox venturi aeration system to guarantee a dissolved oxygen concentration of not less than 2mg/l DO (Figure 2). Blowers to provide the necessary air to facilitate 'bio removal' according to the parameters determined in the pilot trial feed the submerged aeration plant.

    Figure 2: Jetox venturis installed in the bioreactor.

    The incoming effluent is efficiently mixed within the 4,000m3 bioreactor tank with the MLSS. This mixed liquor is drawn from the tank continuously by a series of pumps, to the UF filtration units, which are operated in a feed and bleed modus (Figure 3). The ultrafiltration membranes were specified to allow for passage of treated permeate, but retaining the solids/biomass.

    Figure 3: Ultrafiltration membrane plants installed in Lorca.

    The plant is designed on a 23 hour/day basis and with sub-units to prudently provide for spare capacity and downtime

    due to back washing, without detriment to discharge volume. The plant, therefore, allows for passage of nominally 5,000m3/day of permeate from the bioreactor to the reverse osmosis treatment plant. The residual COD (<400mg/l), BOD (<10mg/l) and ammonia concentration (<35mg/l) of the MBR permeate is significantly reduced by 90-100% and is a considerable improvement on current effluent qualities achieved with conventional treatment.

    The MBR was shown to be an excellent pre-treatment prior to Reverse Osmosis technology, due to the high removal efficiency of suspended solids and organic compounds.

    The high quality permeate reduces bio-fouling and scaling of the subsequent RO treatment and, therefore, improves the overall RO treatment performance. The UF permeate is collected in a 500m3 holding tank and continuously transferred to three Reverse Osmosis units. The RO plant operates in 'Christmas tree' configuration and is operated at a permeate recovery of 75% and produces 158m3 permeate and 52m3 concentrate per hour (Figure 4).

    Figure 4: Reverse osmosis membrane plants installed in Lorca.

    The conductivity of the RO permeate shows a significant reduction of 98% and has a better quality with average 340µS compared to the 770µS of the local tap water. Figure 5 shows the overall plant performance, achieving a reduction of all relevant wastewater parameters including COD, BOD, suspended solids and conductivity to close to zero.

    Figure 5: Overview of the plant


    BLC have successfully designed and commissioned an industrial scale MBR for tannery wastewater treatment currently operational for a tannery cluster based in southern Spain.

    The plant shows excellent pollutant removal efficiency of up to 92% COD and 99% BOD.

    Due to the reduction of suspended solids and organic compounds, MBR treatment can be considered as the preferable technology to prevent bio-fouling of the subsequent RO treatment. This technology shows specific advantages over conventional activated sludge systems or plain membrane filtration, due to the high effluent quality combined with a degradation of organic pollutants.

    The surplus sludge generation can be reduced to 8-10% of the organic load, in comparison with conventional systems where approximately 50% surplus sludge is generated. The industrial scale RO treatment showed, at 75% recovery rate, a highly reduced conductivity of the final effluent of 337µS which was of a better quality than local tap water, enabling water re-use for irrigation.

    The economic feasibility was calculated for the industrial scale MBR and RO plant, treating wastewater of 25 local tanneries in Lorca, Spain. The calculations are based on the MBR and RO plant with 5,000m3 treatment capacity per day using the system discussed.

    Taking into account the overall energy costs for ultra filtration, RO membranes and aeration and capital depreciation, the costs for treating effluent for this plant are less than €1/m3. This is comparable to conventional industrial effluent treatment costs with the advantage of high quality water recovery and re-use.

    Created by:LANCEY, Ms. Raphaelle 31/10/2007 12:45:38 PM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 10:17:41 AM

    TA.1.3. - Salt Free Pickling

    Elimination of salt from pickling - March 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 10:18:01 AM

    Laboratory and industrial trials in Italy have shown that salt free pickling can be achieved. G Manzo and G Maffei from Stazione Sperimentale delle Industria delle Pelli e Materie Concianti - Naples, explain their findings. This paper is based on the presentation given by Dr Manzo at the XXVII IULTCS congress held in Cancun, in May 2003.


    The possibility of carrying out the pickling process in the absence of sodium chloride has been investigated. The results show that this is possible to achieve. In fact, the resulting swelling is almost completely suppressed in the following phase of chrome tanning.

    The leathers, after retanning, dyeing, fatliquoring and staking, present chemical, physical and organoleptic properties which are as good as standard pickled pelts.

    An improved alternative of the studied process is also shown together with the acids with small amounts of chromium salts. In this case, swelling was reduced and the samples were perfectly comparable with the control treated with sodium chloride.

    The resultant leathers showed chemical, physical and organoleptic characteristics equal to those of the standard. The results were confirmed by semi-industrial trials under tannery conditions. Ongoing investigations at SSIPMC are looking into applying the salt free method to hide and skin preservation.


    The elimination of sodium chloride from wastewaters represents one of the most difficult problems which the tanner has to resolve. The extreme solubility of common salt and its great inactivity to precipitation could ultimately compromise the tanning industry.

    Unfortunately, actual technology and knowledge do not allow us to avoid its use because of the irreversible damages which would be produced on the hides during pickling. Acid treatment promotes the deactivation of negative charges on the carboxylic groups of the collagen side chains. As a result, it unbalances the equilibrium in favour of the positive charges of the side-aminic sites. Repulsive forces are then produced within the structure which keep the polypeptide chains at a distance from one another. Therefore, spaces are generated where the water quickly penetrates, producing the swelling. Under these conditions, osmotic pressures, up to 400 atms, are developed, which can cause the complete breaking of the bonds among the protofibrils (elevated state of swelling) leading to a serious destabilisation of the structure1.

    The presence of sodium chloride with the acid avoids the development of this destructive phenomenon. The addition in the bath of sodium chloride increases the ionic concentration of the external solution by increasing the osmotic tension.

    Such an increase makes the external solution hypertonic along with the water contained inside the fibre structure. A transfer of water, from the inside towards the outside, is caused with evident dilution.

    The dilution produces a great dissociation of the acid and the salt, whose ions will be forced to separate through the interfibrillar spaces to the aminic and carboxylic groups of the side chains. The process is completed when the concentration inside and outside the fibrils results in perfect equilibrium.

    When the hides are adequately dehydrated, the carboxylic functions are completely uncharged and the aminic sites will be present in the form of salts. The hide will be ready for mineral tanning.

    If there is a considerable increase in the ionic concentration of the external solution, the same result can be reached by the employment of products different from sodium chloride. It is known that a notable increase of the acid concentration in the pickling reduces the swelling until it corresponds to the isoelectric point.

    Water has a substantial role in the swelling. In fact, the water flow, or its outflow, between the inside and the outside of the hide may or may not produce this phenomenon. Water controls the ionic concentration and, therefore, the employment of sufficient water quantities in the pickling is significant.

    Presentation given by Dr G Manzo, SSIPMC, at the XXVII IULTCS congress held in Cancun

    These discussions leave out the role developed by the so-called 'non-swelling' acids. Many have an aromatic structure, which produces bipolar forms, useful for a stabilisation of the structure by crosslinking. Such links increase the effect of the repulsive strengths between the chains and so repress the swelling2,3,4 in the same way as aldehydes act5.

    The final study explores the employment of a mixture of non swelling acids together with reduced amounts of sodium chloride (solution at 2Bé for sodium chloride) and formate, or a strongly complexed chrome salt and formate mixture. At the end of pickling, the addition of chrome sulfate at 33% Bs Schorlemmer6 is added.

    This work is similar to research performed at SSIPMC some years ago in order to eliminate the deliming and pickling steps7,8.

    In this investigation, the effect produced on the swelling of the hides in the pickling process was studied. The acids used (sulfuric and formic acid) in this process were either in the presence of varying quantities of water or small amounts (2%) of 33% basic chromium sulfate.

    In the latter studies, the high acidity of the bath and the presence of the sulfuric and formic acids during the complexing action, prevent the Cr (III) from forming crosslinks within the collagen structure and, therefore, the salt operates as a deswelling agent. Such a function is created by the peculiar activity of the sulfate ions, which show some tendency to generate crosslinks between the protofibrillar units, making them stable. At the end of pickling, the remaining amount of chromium sulfate is added and the tanning process completed. In acidic conditions, chrome tanning is performed. In both cases the level of swelling was studied after tanning. The observations and results obtained are described as follows.




    As mentioned, two experimental possibilities have been considered. The first had the aim of varying the quantity of water added to the bath in order to study the swelling variations as a function of the ionic concentration. The second investigated improvements that could be obtained by adding small quantities of chromium salt to provide a deswelling and not a fixing action.

    In both cases, after studying the swelling action during pickling, followed by chrome tanning in the same bath as pickling, the sides were retanned, dyed, fatliquored and finished. On the final leathers, chemical, physical and organoleptic characteristics were evaluated compared with the control. Post tanning operations were only performed on samples which showed organoleptic properties which were more or less satisfactory with commercial leathers. The method of pickling that gave the best results was transferred to a semi-industrial scale at a tannery in Naples.


    Hides: For all trials, bovine hides in the limed state were used.

    Chemicals: All the chemicals used in this study are commercially available. The chrome salt used was chrome sulfate at Bs 33% Sch.

    Swelling variation study

    The limed hides were delimed and then pickled using diluted sulfuric and formic acid. The pickling operation with and without chrome was carried out using a typical overnight process with further additions of acid in order to achieve a hide pH of around 3.

    Pickling in the presence of increasing amounts of water

    The quantity and type of acids were the same. The amounts of water varied in the two initial phases of addition, shown as follows:

    At each step, the sample weight, a measurement of hide swelling, the pH of the solution, a cross-section of the hide and the hide appearance were evaluated. The results were compared with the control process, which were 80% water and 6% sodium chloride, with the same acid additions.

    Following pickling, chrome tanning was carried out by addition of the chrome salt to the pickle bath. The final appearance and the swelling of the leathers was evaluated and compared with the control. The wastewaters were analysed for the presence of nitrogen.

    The method that used the highest quantity of water, strangely, resulted as giving the best results as it produced a wet-blue material similar to the control. In this case, the distribution of the chrome inside the cross-section of the hide was analysed.

    The chromed tanned leathers were then shaved, retanned, dyed and fatliquored using the same tannery that provided the limed hides. The tannery technicians noted that the physical and handling properties of the finished leathers were a good comparison with their own production. Chemical and physical analyses were also carried out.

    Pickling in the presence of small quantities of chromium salts

    Additionally, the effect on the swelling produced by the addition of reduced amounts of chrome salt in the bath of pickling was analysed. The treatment process can be seen in Table 3.

    As the experimental method evolved, studies of the levels of swelling and pH of the solution and hides were evaluated.

    Such evaluation, in particular the swelling development, was extended to the tanning and the basifying process steps. For basifying, it would be more suitable to talk about the weight increase as the hides have absorbed the tanning and basifying products.

    Following pickling and tanning, the condition of the hides was observed and compared with the pickled control that was tanned in the presence of sodium chloride. The wastewaters were analysed to determine the eventual presence of nitrogen as this indicates possible structural damage. On the chrome tanned leather, analyses were performed in order to monitor the chrome distribution through the cross-section.

    Subsequently, this technology was applied to the pickling and tanning of the three matched-side hides. Following shaving, the sides were retanned, dyed and fatliquored at SSIMPC and, finally, finished by the tannery.

    The finished leathers were subjected to chemical, physical and organoleptic analysis. The technical staff at the tannery evaluated the handle and appearance.

    Results and discussion

    Figure 1 shows the weight increase of the hides (or swelling), during the process of pickling as a function of the percentage of water used. The results showed that the swelling, for the same pH value, increased when the quantity of water was increased to reach the maximum value of 30%. Above this value, the swelling is practically independent from the dilution.

    This phenomenon shows that starting with a certain quantity of water, the inflow of water directly into the inside of the hide is balanced by the outflow directed toward the external solution. Such an outflow increases the dissociation of the ions and favours their entrance into the hide, producing a neutralisation of the charges or the activation of the positive charges. As soon as the equilibrium is reached, any dilution up to 60% and over, does not influence the swelling mechanism, ie the entrance of water.

    Clearly swelling results for an equal amount of water are dependent on the final pH, reaching the maximum value at the end of the pickling, pH3.0.

    This can be explained by considering that by lowering the pH, it produces an increase of positive charges into the hide. This promotes a stronger repulsion between the polypeptide chains with the formation of larger spaces where the water flows.

    In every case, the presence of the sodium chloride, (Figure 1), completely eliminates the phenomenon of swelling, independent of the value of the final pH and the overall water quantity used. The strong increase of the ionic concentration makes the external solution hypertonic compared with the water contained inside the fibre structure of the hide. This causes a release of water from the inside toward the outside, preventing swelling. The quantity of water absorbed does have consequences for the final physical state of the hide.

    Table 4 shows the aspect of the hides at the end of the pickling.

    It was predicted that the samples, treated with 30 and 50% water in the absence of salt are more firm and rigid than those pickled in the presence of the lowest quantities of water. These samples have a soft touch similar to that of the hides pickled in presence of sodium chloride. The study of further variations, induced by the swelling, in the following process of tanning gave interesting results. Figure 2 shows that the modifications to the same pickled samples with the tanning and basifying process are represented together with the swelling variations in pickling.

    The tanning and subsequent basifying decreased the weight of the pickled hides. The swelling results were reduced and were closer to the leathers treated in the presence of sodium chloride (control with 80% water).

    In the case of pickling with only 10% water, the weight of the hides was, after tanning, practically identical to the control. This means that water outflow, produced by the addition of the chrome salt and the bicarbonate, is much more consistent when pickling is carried out in the absence of sodium chloride. The pickled samples with sodium chloride show a strong increase in weight after tanning and basifying.

    Nevertheless the differences mentioned can be considered as the result of the absorption of the tanning and basifying products rather than water, which always results in an outflow of water. This means that the water causing swelling, which is effectively present at the end of the tanning, is decidedly less important than that which is calculated by the weight differences.

    If we consider that the weight increase of the hides - in a traditional pickling process followed by chrome tanning - depends exclusively on the absorbed substances from processing. The real swelling in the absence of salt corresponds, after tanning, to no more than 20-25%, using the maximum water quantity during pickling.

    In such a case, we could not show that the increases are only due to the water absorbed, because the percentages of chrome found in the hide are decidedly higher than the control (Table 5).

    This shows that the acid swelling is not an irreversible process but reversed as much as alkaline swelling that is produced in the unhairing and liming processes.

    Table 4 shows that the only crosslinking during tanning completely modifies the appearance of the pickled hides. The hides pickled with the maximum amount of water, which were previously swollen and rigid after tanning and basifying, were similar to the standard with an absence of rigidity and with adequate flexibility. These samples were analysed to verify the distribution of the chrome.

    Figure 3 shows the values of nitrogen in the final wastewaters following tanning and basifying. The results show that the nitrogen levels are very low and suggest that the acid attack during pickling without salt has not produced any structural destabilisation.

    The small amounts found can be attributed to the last traces of impurities caused by bating. This is confirmed by small quantities of nitrogen found in the final wastewaters of the control hides.

    Differences are observed on the distribution of the chrome along the cross-section of the leathers in comparison with the control (Table 6).

    From the data in Table 6, it emerges that pickling in the presence of sodium chloride guarantees a more homogeneous distribution of the tanning agents in comparison with the sample treated with the new experimental method.

    Considering the results and in particularly, the appearance of the hides after tanning, the experiment on three match-sided hides used a new pickling technology without salt in presence of 50% of water.

    The obtained wet-blue was shaved, retanned, dyed and fatliquored according to processes used by the tannery which supplied the limed hides. Then the hides were dried, staked, finished and finally tannery technicians assessed the appearance of the leathers.

    According to their judgement, the leathers were comparable enough with those normally produced by the tannery. The final side leathers were analysed to assess their chrome and fat content and physical properties. Table 7 shows the chemical analysis.

    According to the results, there are no great differences between the leathers treated with the new technology and the standard procedure. Many positive considerations can be made by the comparison of physical properties (Table 8).

    Despite the less even distribution of chromium throughout the cross-sections of the experimental samples, as shown in Table 6, the new pickling method can still be used according to our overall results. Better results can be obtained by applying another method which uses lower quantities of chromium in the pickle without salt.

    Figure 4 shows the increase in weight (swelling) of the hide during the pickling until a pH of about 3.0. In such a case, the water used is constant and the swelling results only as a function of the pH.

    The differences in the weight increase between the control and the sample treated without salt are lower than the treatments previously mentioned. This is caused by a repressing action induced by the small amounts of chrome salts, which strains the water contained in the hide, limiting the capacity to swell.

    After pickling, the increase in hide weight corresponds to about 15%, while the control value is around 6%. This difference is almost cancelled out after tanning and basifying. Results in Figure 5 consider that the increases in weight in comparison with the control are only the consequence of the higher absorption of the chrome salt and bicarbonate (Table 9). The appearance of the hides after pickling and basifying results in equal values to the control. The final condition of the grain gave excellent results without wrinkles and adequate flexibility. The quantity of nitrogen in the bath at the end of tanning was also negligible. Analysis of chromium in the leather (Table 9) shows a distribution slightly inferior to the control sample. As mentioned, the three sided hides were treated according to a standard control and the new pickling technology. The organoleptic aspect, chemical and physical characteristics of the final materials, were evaluated.

    Once more the hides were tanned, shaved, dyed, retanned and fatliquored using the same tannery recipe. The leathers were then staked and finished. Technical tannery staff evaluated the handle and appearance of the leathers.

    According to their judgement, the experimental leathers corresponded fully to their production standard and were perfectly acceptable. The results of chemical and physical analyses are seen in Tables 10 and 11. It can shown that the actual process of pickling, with the employment of suitable quantities of sodium chloride, can be replaced using this experimental technology to obtain final leathers with the same chemical, physical and organoleptic characteristics as the control.

    The application of the two studied methodologies and, in particular, the second which includes small quantities of chromium salt, provides a dramatic reduction in NaCl from the wastewaters.

    Semi-industrial trials carried out in tannery conditions according to the second method have fully confirmed the results according to studies at the Stazione Sperimentale Pelli.


    This paper shows a possibility of eliminating the sodium chloride from the process of pickling and tanning, without varying the type of acids and the process. In spite of all the reported literature, pickling can also be performed in the absence of sodium chloride, or any other salt, without producing any destabilisation. In fact, acid swelling is reversible in a similar way to alkaline swelling in deliming.

    Acid swelling is subsequently reduced in the following process of chrome tanning. The final leathers, apart from a less uniform chromium distribution, are comparable with those of the traditional process for chemical, physical and organoleptic properties.

    An improvement can be made by the employment of small quantities of chrome salt during pickling. In these conditions, the chrome salt provides a strong deswelling action as it makes the external solution hypertonic. This forces water to flow out from the inside toward the outside of the hide. The final consequence is a very reduced swelling similar to the standard method.

    Tanning follows in the same bath as the pickle with the addition of the remaining quantity of chrome salts. The final leathers show chemical, physical and handling characteristics similar to the control standard. This final method has been applied to semi-industrial trials, which have confirmed the results mentioned previously. Therefore, it is possible to eliminate sodium chloride from the pickling process without any major variations to the final characteristics of the leather.

    Stazione Sperimentale Pelli is now looking at how to eliminate sodium chloride from the preservation of raw hides and skins.


    1. G Manzo: Chimica e Tecnologia Conciaria, Ed Media Service Rescaldina (VA), pages 123-128, 159-160, 1999.

    2. G Otto: J Am Leather Chem Ass, 53, 298, 1958.

    3. D Post: J Am Leather Chem Ass, 59,670,1964.

    4. K A Shanmugasundaram; V S Venkata Boopathy; Sundara Rao: Leather Science, 34, 157, 1987.

    5. A Lauton: Atti V Congresso Mediterraneo, Sessione 'Environment', Atene, 1993.

    6. R Palop: Ass Quim Española Ind Cuero, 51, 129, 2001.

    7. A Simoncini; L Del Pezzo; G Manzo: Cuoio Pelli Materie Concianti, 44, 559, 1968.

    8. A Simoncini: L Del Pezzo; G Manzo: Cuoio Pelli Materie Concianti, 15, 506, 1969

    Created by:LANCEY, Ms. Raphaelle 31/10/2007 2:20:38 PM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 10:18:01 AM

    TA.1.4. - Doubleface

    Factors influencing dyeing of doubleface sheepskins (Part I) - April 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 2:18:42 PM

    Dr Ramón Palop, Cromogenia-Units, Barcelona, Spain, explores the factors influencing wool dyeing on doubleface sheepskins. The study looks at different dye types and the effects of temperature and pH during the dyeing operation.


    The dyeing of wool in sheepskin production is conditioned by three main factors, namely: a) substratum to be dyed, b) dyestuffs used, and c) dyeing method. The substratum, which is the wool, consists of a wide variety of types in respect of fineness (merino, crossed, entrefino types).

    Furthermore, the effect of the environment in which the animal has lived and its age both influence whether the wool is in better or worse condition.

    All this means that the chemical composition and physical arrangement of the quality of the wool varies between skins, and even within a single skin, depending on the area concerned.

    All these are the properties inherent to the animal, but there is another important factor and that derives from the treatment to which the skin has been subjected during the tanning process. This affects the physico-chemical transformation undergone by the wool, such as processes of oxidation reduction in bleaches or washes, and the quality of tanning product (chrome, aluminium etc) fixed or deposited on the wool, together with a certain quantity of grease whose nature or composition can have a varying influence on dyeing.

    We may state, finally, that if the wool has undergone a process of ironing or glazing, the chemical and physical composition vary extraordinarily according to the composition of the ironing liquids and temperature of the ironing roller.

    The types of dyestuff most widely used in wool dyeing are: a) acid dyestuffs, b) metal-complex dyestuffs, c) mordant dyestuffs, d) reactive dyestuffs and e) vat dyestuffs.

    In this work, we will restrict ourselves to studying those of types a) and b), as they are the ones most frequently used.

    Figure 1

    Acid dyestuffs

    The acid dyestuffs are generally sodium salts of sulfonic acids, typical ones being C.I. acid orange 10. C.I. acid blue 45, and C.I. acid blue 1, which represent the azo, antrochinoid and triarylmethane classes, respectively.

    The molecular weight of most of the acid dyestuffs is of the order of 300 to 800. The molecules of the dyestuffs are composed of a large anion which contains from one to four acid sulfonic groups, associated with the corresponding number of small sodium cations. Despite their high molecular weight, the free sulfonic acids, whose dyestuffs are sodium salts, are acids almost as strong as sulfuric acid. Their pKa values range between 1 and 2, and the solutions of their solid salts are neutral.

    Owing to their large size and their water-repellent character, the anions of acid dyestuffs show a considerable attraction to each other. This leads to the formation of aggregates.

    In general, the higher the molecular weight and the lower the number of acid sulfonic groups, the greater the tendency to aggregation.

    This aggregation is encouraged by the presence of acids or salts in the bath, while temperature increase reduces the tendency.

    The molecule takes on an electronegative character, being considered as a weak acid insoluble in water.

    The alkaline salts are partially soluble in water and can be used following dilution with a dispersant.

    Solubility in water increases if groups which are not sulfonic groups as such but non-ionic groups, are added to the dyestuff molecular. The most common of these are the sulfamide groups: -SO2HN2-.

    The 1:2 metal-complex dyestuffs can take four forms:

    1 Acid form

    2 Alkaline salt

    3 With non-ionic water-solubilising agent

    4 Monosulfonic mixed complex

    Of these four types, the weaker their solubility in water, the better they will bond to the wool and less onto the leather (types 2 and 3); of these we must choose the most water-repellent and employ them under the best conditions for dyeing.

    When we deal with the dyeing of leather, we will see the type of conditions best suited to application.

    The studies we made in 1980 went more deeply into the response of the acid and 1:2 metal-complex dyestuffs in wool dyeing.

    Spanish merino-type skins with wool characteristics as similar as possible to each other were taken as the starting point, so that the various methods used in the tests used an homogeneous substratum.

    The chemical properties of these skins, both for wool and for leather are as given in Table 1.

    The skins having been tanned and fatliquored, were dried and then conditioned following optimum setting out. The wool was then ironed using an alcohol solution, formic acid and formol, three times at 170ºC, and then sheared to 17mm.

    Following the dyeing treatment of each variable, a part of the dyed skin was taken and the wool removed with a knife. This piece was then submitted to the extraction treatment described below.

    We have calculated an 'extractability factor' for each type of dyestuff, based on the following method: de-woolled skin with identical tanning as the doubleface was treated with the same dye. We could use spectrophotometry to determine the quantity of dyestuff absorbed by the leather.

    This leather was subjected to the following stripping process: prior treatment with 1% ammonia at 50ºC for four hours and three washings with distilled water at 50ºC for two hours for each washing.

    Once the skin had dried it was submitted to treatment with perchloroethylene at 45ºC twice for three hours. In case of the acid dyestuffs we, thereby, extract 87.5% of the fixed dyestuff, of which 74.5% was obtained with the alkaline treatment and 13% in treatment with the solvent.

    In the case of 1:2 metal-complex dyestuffs the results were: extraction of total of 59.8% of the fixed dyestuff, of which 9.5% pertained to the alkaline treatment and 50.3% to the treatment with solvent.

    All the tests were carried out on pieces measuring 10 x 10cm, with the following analyses and the variables described above being found.

    The following dyestuffs were used:

    Acid orange 3

    Acid red 88

    Acid blue 25

    The reference taken was the dry weight of the conditioned skin, with wool sheared to 17 mm, bath ratio of 1:20 and 0.5% dyestuff. This 0.5% does not refer to the weight of the commercial dyestuff since, of course, the concentrations of dyestuffs of equivalent absorbency are at the maximum of their spectrophotometic curve.

    Wool dyeing process
    Bath ratio 8l/skin
    Soaking - retanning

    Water at 40ºC
    1.5g/l Celesal K
    Run for 60 min
    3.0g/l Chrome salt 33ºSch
    3.0g/l Retanal CP Super
    Run for 60 min
    2.0g/l Sodium formate
    Run for 60 min. pH = 4.2. Run off. Rinse for 15 min with cold water
    Water at 30ºC
    2.0g/l Sodium formate
    Run for 10 min
    2.0g/l Retanal NS
    Run for 10 min
    1.0g/l Sodium bicarbonate
    2.0 Run for 60 min. pH = 6.0
    Run off and rinse for 10 min
    Wool dyeing
    Water at 62ºC (maintained)
    0.5g/l Dyeing auxiliary product
    Run for 30 min
    x g/l Acid or metal-complex dyestuff
    Run for 15 min
    0.5g/l Formic acid
    Run for 30 min
    0.5g/l Formic acid
    Run for 30 min. pH = 4.2. Run off and rinse for 15 min.

    Influence of pH

    Six pH variables were carried out, these being 4.2, 6.2, 7, 7.5 8.1 and 8.6. The baths were set at these pH values, after having achieved equilibrium between bath and skin, that is, when at 90 minutes of treatment the pHs remained constant.

    Samples were taken every 15 minutes and these were used to draw up the exhaustion curves of Figure 1, from which we can see that for each dyestuff exhaustion increases as pH decreases.

    Comparatively, it can be seen that the yellow is exhaustion less in curve number 1 (95%), while the red and blue are almost totally exhausted (97%) at the same pH.

    As the pH increases, the yellow is affected most, followed by the red and then the blue.

    Fixing on the suede also increases with the pH, as can seen in the upper scales of Figure 1, both in absolute and relative values, at the set total quantity of fixed dyestuff.

    Comparing them, for equal pH values the quantity of dyestuff fixed on the suede increases in the order, yellow, red and blue.

    The pH of the bath is an aspect of vital importance. From the equation 4.1 below, it can be deduced that when the wool combines with the acid:

    Equation (4.1)
    R - +NH3-OO - C - R + -ClH+ oNH+ H2Cl- + HOOC - R

    The ionisation of the carboxyl groups is inhibited and the fibre takes on a positive charge which is neutralised by the absorption of the inorganic anion. The positive charge increases with the quantity of acid present, reaching its maximum at pH1 approximately. In the case of the simpler acid dyestuff, that is those of a lower molecular weight and lower affinity, the dyeing is carried out at pH2.5-3.0, obtained with the addition of sulfuric acid.

    In the case of dyestuffs of greater molecular weight and high affinity (equation 4.1). This will lead to a very fast adsorption of the dyestuff, which due to its high affinity will not travel to other basic groups. It may, therefore, be necessary to renounce the use of acid, in which case the reaction of the wool, on the basis of an essentially neutral bath (pH7), can be presented by the equation 4.2 shown next:

    Equation (4.2)
    R - +NH3-OCC - R + Na dyestuff o +RNH3 dyestuff + Na +OCC - R (4.2)

    This means that the amino groups of the wool are now involved, although the non-polar forces are mainly responsible for the affinity of the dyestuff. It can, therefore, be established that the three dyestuffs studied are of medium affinity, increasing in the order yellow, red, and blue.

    Influence of temperature

    Six variables were implemented, with each of the three dyestuffs, at temperatures of 40, 45, 50, 55, 60 and 65ºC. The dyes started at pH 7.5, and after 15 minutes formic acid was added to pH6, while after 45 minutes acid was again added, this time to pH4.3. The treatment lasted another 45 minutes, until 90 minutes dyeing time was completed.

    The curves obtained are shown in Figure 2, in which we can see that for three dyestuffs the six curves are exhausted at the end of the 90 minutes, the red and the blue showing similar response and becoming exhausted quickly, while the yellow became exhausted slightly more slowly.

    Figure 2:

    The quantities of dyestuff fixed in the suede increase as the temperature diminishes, for each dyestuff, while comparatively, and at equal temperature, the amount of dyestuff fixed in the leather increases in the order yellow, red and blue.

    Increasing the dyeing temperature has a triple purpose: 1) to prevent aggregation of the dyestuff; 2) to increase swelling of the fibre and thus make the dyestuff more permeable; 3) to accelerate diffusion of the dyestuff within the fibre.

    That is, the higher the temperature, the more the dyeing will take place with a higher concentration of dyestuff at the wool-bath surface.

    Of the three dyestuffs studied, the yellow showed a greater tendency to form aggregates than the red and the blue.

    Influence of auxiliary products

    Four variables were implemented, with each of the three dyestuffs, corresponding to curves 1, 2, 3 and 4 (Figure 3).

    Figure 3:

    The treatment was carried out, respectively, with the following products: curve nº1, oleilamine, nº2 nonylphenol (8 moles of ethylene oxide), curve nº3 without any product, and curve nº4 with sodium sulfate.

    As can be seen in Figure 3, with the three dyestuffs, the speed of increase followed the same order as their curve number, with the final exhaustion being the same order as their curve number, with the final exhaustion being the same for the red and blue, while for the yellow curve nº4, that is, with the addition of sodium sulfate, the rise of the dyestuff is retarded a little, and the final exhaustion is slightly lower than in curves 1, 2 and 3.

    The fixing of the dyestuff in the leather increases according to the order of the curve, and if we make a comparison between the three colours we see that for a given auxiliary product the quantity of dyestuff fixed in the leather increases in the order yellow, red and blue.

    In general the wool absorbs the acid dyestuffs due to three different forces of attraction: 1) Ionic attraction between positive acid groups of the dyestuff and amino groups of the wool also charged positively; 2) Van Der Waal's forces, non-polar and exercised between the water-repellent dyestuff anion and the parts of the wool of the same type adjacent to the positively charged amino groups, and the covalent bonds, which are responsible for the strongest unions and, therefore, play a direct role in fastness levels.

    In the case of the acid dyestuff we are looking at, the three types of bond are important, and the acid must, therefore, be present to ensure the existence of a positive charge in the fibre, while the presence of additional sulfate ions promotes the competition of the basic points, leading to de-adsorption and levelled dyeing.

    Furthermore, the function of the oleilamine is to react with the sulfonic groups of the dyestuff, transporting the molecule of said dyestuff to the positively charged amino groups of the wool in acid medium, thus facilitating their fixing.

    Metal-complex dyestuffs

    Chemically, the metal-complex (or premetallised) dyestuffs are very closely related with the metal complexes produced in the fibre by mordant dyestuffs, so that from the classification point of view, they are acid dyestuffs, treated as such in the Colour Index.

    From the earliest times, mordanting has been associated with good dyeing fastness.

    As we know, oxidation dyeing consists in depositing the metal atoms on the fibre and then producing the complex in situ by the oxidation of various organic compounds.

    The mordanting operation naturally prolongs the dyeing process, so it was only normal that a method should be sought to permit a combination of metal (normally chromium, cobalt or iron) and the colour prior to dyeing.

    Given that the 1:2 types are the ones mainly used for dyeing, our study will look at these.

    We shall give the term 1:2 metal-complex dyestuff to those which have a metallic atom, forming a complex with two molecules of dyestuff (4). These generally correspond to acid/dihydroxyazoic or dihydrox/carboxyazoic dyestuffs; the metallic atom can be any of those mentioned above.

    If the two dyestuff molecules are of the same constitution, the 1:2 metallic dyestuff is termed 'symmetrical', if not, it is 'asymmetrical' or mixed.

    Its general structure corresponds to the following schema:

    The following dyestuffs were used:

    Acid yellow 118

    Acid orange 89

    Acid black 63

    The same procedure was followed as for the acid dyestuffs.

    Influence of pH

    Six variables were implemented (curves 1, 2, 3, 4, 5 and 6), with the corresponding pHs of 4.2, 6.2, 7.0, 7.5, 8.1, 8.6.

    In Figure 4, it can be seen that with the three dyestuffs, the exhaustion increases as pH diminishes; the three, therefore, show a very similar response.

    Figure 4:

    The distribution of the dyestuffs between the suede and the wool takes place in such a way the quantity fixed in the leather increases as pH increases. The increase is only in proportion to the total fixed, however, since in absolute terms it diminishes.

    Compared with the acid dyestuffs, they can be said to undergo less exhaustion for similar pH levels, and their curves have less slope.

    Likewise, as the pH rises there is a reduction in the absolute value of the quantity of dyestuff fixed in the suede, while the acid increases, although the performance on wool of the same quantity of dyestuff at the same pH is greater with the acid dyestuffs.

    This behaviour of the metal-complex 1:2 dyestuffs is explained by the negative charge of the complex, which makes them sensitive to the pH variation, although less so than the acid dyestuffs, probably because the charge is not localised. As the molecule is large, the covalent bonds and Van der Waal's forces act powerfully, providing good fastness properties.

    Influence of temperature

    Six variables were implemented (curves 1, 2, 3, 4, 5 and 6), corresponding to temperatures of 65, 60, 55, 50, 45 and 40ºC. Figure 5 shows how exhaustion increases as temperature increases, for all three dyestuffs.

    Figure 5:

    The curves are also similar in all three, although for the yellow at 90 minutes the curves become more horizontal as temperature increases, while for the orange and black they retain a certain slope, which indicates that the dyestuff could become even more exhausted.

    The distribution of the dyestuffs between wool and suede takes place in such a way that for all three, the quantity of dyestuff fixed in the suede decreases slightly as the temperature decreases in absolute values, as it does in relation to the total quantity of dyestuff fixed. These differences increase in the order yellow, orange and black.

    If we compare against the influence of pH with temperature, we see that the pH variation has a greater effect than temperature variation on total fixation of the dyestuff; and the quantity of dyestuff fixed in the suede is higher than in the case of pH variation.

    As they have large molecular size, the 1:2 metal-complex dyestuffs show a great tendency to form aggregates and the temperature in such cases, therefore, has to be high to provide the dyestuff molecules with sufficient energy to overcome the energy barrier at the wool-bath surface divide.

    Influence of auxiliary products

    Four variables were implemented (curves 1, 2, 3 and 4), corresponding to the products: tributyl phosphate; phosphoric ester in emulsion with nonyl phenol with 6 moles of ethylene oxide; without any product; and, finally, with sodium sulfate. The exhaustion curves for each of these dyestuffs increase to 90%.

    The curves of the different products (Figure 6) cut across each other owing to the kinetics of the reaction being different according to the medium in which the dyestuff is placed; that is, a dyestuff in a certain medium begins with fast exhaustion and then rises only slowly, while the same dyestuff under the same conditions, but in a different medium, may show the opposite pattern of exhaustion, that is, first rising slowly and then doing so more rapidly.

    Figure 6:

    In any case, the four curves differ little from each other, though the distribution between wool and suede is different.

    We can generalise by stating that for the three dyestuffs, with 90% of dyestuff fixed, the phosphoric ester with nonyl phenol mixture leads to most fixing of dyestuff on the wool (at 33%), followed by tributyl phosphate (with 30%), then the blank test without product (20% fixed), and lastly the sodium sulfate, which fixes the least quantity of dyestuff on the wool (10%).

    The influence of the auxiliary products on wool dyeing with metal-complex dyestuffs is very large. Given the considerable complexity of this particular subject, however, a special study would have to be devoted to the use of solvents and/or emulsions.

    The exact role of the solvent is difficult to determine, although it is considered to be essentially a physical action, without direct participation in the reaction between the dyestuff and the wool fibre. It has a disaggregation action on the dyestuff, but above all it enhances contact between the dyestuff and the wool, dyestuff being absorbed mainly into the fibre of the latter, which leads to stronger concentration of the dyestuff in that place.

    Where an emulsifying agent is used it plays an important role, as it orients itself on the surface of the wool and maintains the solvent in suspension, and this is the factor in determining a concentration of solvent on the interface surface sufficient to really influence the dyeing speed. Furthermore, the emulsifying agent must not combine with the metal complex or with the wool. This is so that the dye distribution mechanism between the two solvents is not disturbed.


    1. In sheepskin dyeing with acid dyestuffs, as the pH diminishes fixation increases, reaching 98%; there is also an increased quantity of dyestuff fixed in the wool.

    2. As temperature increases in dyeing with acid dyestuffs between 40 and 65ºC, the exhaustion rates do not change but dyestuff distribution does, fixing more on the wool as temperature increases.

    3. The addition of various auxiliary products does not alter the exhaustion rate of the acid dyestuffs but it does alter their distribution between wool and suede.

    4. In dyeing with 1:2 metal-complex dyestuffs, as the pH diminishes the total fixation of dyestuff increases, as does its distribution, this being greater in the wool as pH decreases.

    5. As temperature is varied between 40 and 65ºC in dyeing with 1:2 metal-complex dyestuffs, the total quantity of dyestuff fixed alters considerably; however, the distribution between wool and suede retains the same proportions for each dyestuff.

    6. The addition of solvents, emulsions of solvents or a sodium sulfate type salt does not alter the final exhaustion rate, but it does alter the distribution between wool and suede.

    Products from Cromogenia-Units
    (1) Deterpiel PF-14
    (2) Retanal CP Super

    Created by:LANCEY, Ms. Raphaelle 01/11/2007 10:56:36 AM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 2:18:42 PM

    TA.1.5. - Linkages

    Environmental impact on profits and production - May 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 2:25:51 PM

    The results of an investigation into the links between trade and environmental policies in the hides and skins and leather sector were presented at the last FAO meeting in Rome. Work was carried out using a partial equilibrium model based on known or estimated data. While such models may be founded on flawed statistics, so there is huge room for improvement, they do at least provide working hypotheses

    At the seventh session in June 2001, the sub-group on hides of skins requested the FAO secretariat to undertake empirical analysis of the impact of environmental regulations and trade restrictions on the hides and skins and leather sector. This document has been prepared in response to that request and was presented to the eighth session by George Rapsomanikis.

    The impact of environmental regulations, pollution prevention and pollution abatement costs is examined by means of a partial equilibrium model that provides a stylised picture of hides and skins, light leather and footwear global markets. Rapsomanikis explained that models are simplistic aggregations with huge data requirements.

    Leather processing is a polluting activity with the tanneries and leather finishing sector being among the most toxic industrial sectors1. An increase in the stringency of environmental regulations is thought of as having implications for the location of the industry as abatement costs may shift leather processing away from countries with stringent regulations.

    The extent to which environmental regulations across countries determine the location of the processing industry depends on the stringency of the regulations and the corresponding abatement costs. As a generalisation, there is evidence to suggest that developing countries that support their domestic processing sector have environmental standards that are inferior to those prevailing in developed countries, as lower incomes are likely to lead to weak demand for higher standards that improve environmental outcomes.

    Stringent environmental regulations may have resulted in a relative shift of the leather processing industry from developed to developing countries in the past, as the abatement costs of compliance with the regulations might have exerted pressure on profitability. Analysis was hampered by the lack of hard data. For Europe, only soft estimates were available.

    It has been calculated that clean-up costs in European plants might be 3-5% of running costs2. An earlier Unido estimate suggested that effluent treatment costs were around 4-6% of final costs3. Technological developments, as well as the operation of large numbers of tanning plants within 'clusters', have resulted in a reduction in treatment costs.

    In the USA, total expenditure on disposal and recycling in the leather industry for 1999 amounted to US$1 million, while the operating costs for abatement amounted to US$11.8 million4. Based on this data, the only hard figures the FAO secretariat had to work with, it is estimated that the average cost for abating pollution that accrued from processing 1,000 sq ft of light leather in the US amounts to approximately $17.10.

    Presumably, abatement costs in developing countries, where the same stringent standards are generally not met, would be lower but may rise above 5% of operating costs if an attempt was made to meet developed country standards without the technology available in developed countries.

    An increase in the stringency of environmental regulations will result in a corresponding increase in abatement costs. Environmental regulations for the leather processing industry often consist of maximum values for air emissions, liquid effluents and solid waste per unit of production. An increase in stringency would reflect a decrease in these maximum values.

    In the second half of the paper, the discussion focuses on trade liberalisation. Trade policy reform is a priority issue in the WTO negotiations, since trade liberalisation is viewed as encouraging economic welfare and long-term growth.

    The analysis was again carried out by means of the partial equilibrium model of hides and skins and leather products. Such models are increasingly used to address sensitive policy issues, such as the impact of trade liberalisation on production, consumption and trade, the location of industries, as well as on the distribution of benefits and costs across countries and population groups.

    Trade measures, such as import tariffs and export taxes, import and export quotas and tariff rate quotas insulate domestic markets by driving a wedge between domestic and international prices and serve to transfer wealth from one population group to another. The objective of import tariffs and import quotas is to protect producers and processors.

    These policy instruments reduce the degree to which domestic producers or processors are exposed to changes in the international market and provide incentives to increase production by raising the domestic price at the expense of consumers. Such policies are applied for various reasons.

    The objective could be either to support the income of domestic producers or to protect an infant industry until it becomes sufficiently well established to compete with developed countries. On the other hand, export quotas and export taxes aim at depressing the domestic price relative to the international price and redistribute wealth from producers to consumers. These policies aim at increasing the supply of raw materials to the domestic market, lowering prices to producers and domestic processors.

    Paul Pearson, representing the UK, said that from the UK point of view, there is concern about export restrictions because of the impact on the competitiveness of the British industry. 'Our raw materials are freely traded but supplies from certain other countries are not available to our industry. We believe that export restrictions have a negative impact on the suppliers of hides and skins. Firstly they reduce prices and secondly they reduce any incentive to improve the quality of hides and skins.

    'Overall, our sector has been going through major changes - with the growth and shift in capacity to China being a factor that cannot be ignored in any aspect of the hides, skins, leather and leather products sector. We believe the overall long-term situation in the market is that there is a shortage of hides and skins.

    'Quality is a very important and continuing issue. The statistics show a decline in production in countries that have traditionally produced good quality hides and skins and an increase in countries that are considered to produce lower quality. So the long-term position is a growing shortage of good quality raw material - and this is a major challenge for the hides, skins and leather sector.'

    Table 1 presents the tariff rates for bovine hides, light leather and footwear that are implemented by regions of developing and developed countries. Market access in terms of tariffs is a major issue for both raw materials and processed products in markets of both developing and developed countries.

    Average import tariffs for raw bovine hides vary between 0% (North America and Oceania) and 11.7% (Africa). The pattern of tariff escalation is evident with the level of protection, expressed in tariff rates for the developing and developed countries, increasing along the processing chain. Average tariffs for finished leather vary between 2.5% (Oceania) to 16.4% (Africa), whilst those for footwear vary between 5.6% (former Soviet Union region) to 37.5% (Oceania).

    In theory, the elimination of tariff barriers for hides and skins and leather products is likely to increase global economic welfare as it encourages the production of these commodities to take place in regions and countries according to the law of comparative advantage and in line with the availability of resources, such as land, livestock herds, labour and technology. The removal of tariff barriers for raw hides, skins and leather products would be likely to lead to an increase in international prices for raw materials and processed products. Tariff elimination would result in a reduction in prices to consumers in countries that protect their markets, thereby stimulating demand for leather and leather products that in turn would strengthen international prices. Therefore, leather processing is likely to increase and its location is likely to shift following liberalisation.

    The situation may be different in producing countries which have a large hitherto protected domestic market, where liberalisation would result, at least in the short-term, in lower prices with an inflow of imports competing with domestic producers. In the long-term, liberalisation in these countries may result in increased revenues brought about by an increase in competitiveness and efficiency.


    1. H Hettinge, P Martin, M Singh and D Wheeler (1995). The Industrial Pollution Projection System. The World Bank, Policy Department.

    2. FAO 2001 'Trade, Sanitary and Environmental Policy Linkages in the Hides and Skins and Leather processing Sector', CCP: ME/HS 01/3, Rome.

    3. FAO 1994 'Environmental aspects of processing and trade in hides, skins and leather. CCP: ME/HS 94/9. Rome.

    4. US Census Bureau 1999, Pollution Abatement Costs and Expenditures, Washington.

    5. World Statistical Compendium for Raw Hides and Skins, Leather and Leather Footwear, 2001.

    Created by:LANCEY, Ms. Raphaelle 01/11/2007 2:25:51 PM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 2:25:51 PM

    TA.1.6. - Chrome VI

    The effect of organic acids and amines in Cr VI determination - May 2004
    Contributed by: Leather International magazine
    Last updated: 01/11/2007 2:45:55 PM

    This paper was originally presented at the IULTCS congress in Cancun, Mexico, in 2003. CSIRO Leather Research Centre were so interested in the presentation that they then carried out their own research. The authors of this paper are Cameron Simpson, Mark Hickey and Catherine Money.


    CSIRO Leather Research Centre, Australia, were so interested in the paper presented at the IULTCS Congress in Cancun by Kallenberger and Hernandez that they decided to carry out their own research on the effect of organic acids and amines in chromium VI determination since the original authors felt that they had no time to carry out additional work.

    The authors are Cameron Simpson, Mark Hickey and Catherine Money. None of the organic acids or amines they tested generated false positives using the IUC 18 standard method. Tests did show that the diphenylcarbazide solution reacted with the organic acids and amines resulting in colour development. However, the colour was pH dependent and when the extraction solution or phosphoric acid solution was added, the pink/red colour dissipated in all cases.

    Juan Hernandez presenting the original paper in Cancun

    Cameron Simpson

    Catherine Money


    There has been much debate over results obtained from the analysis for hexavalent chromium (Cr VI) in soils and leathers1. Questions concerning the accuracy of the current test method have again been raised, this time regarding potential false positives generated from some compounds found in leather and soil extracts.

    A paper titled 'Organic Acids and Amines Produce Colour with Diphenylcarbazide Determinations' by Kallenberger and Hernandez was presented at the IULTCS Congress in Cancun in 20032. The paper suggested that organic acids and amines may give false positives in Cr VI determinations. There was considerable interest in the presentation and it was concluded that further investigation was required3. The work presented in this report further examines the effect of simple organic acids and amines on Cr VI determinations obtained using the IUC 18 method4.

    The diphenylcarbazide Cr VI method used by Bartlett and James in 19795 was also tested for potential false positive results from spikes of organic acid and amines.


    The IUC 18 chromium VI determination method consists of an extraction phase where the soluble chromium VI is leached from the sample at pH7.5 to 8. The Cr VI in solution oxidises 1,5-diphenylcarbazide to l,5-diphenylcarbazone to give a red/violet complex with chromium. The colour development is highly dependent on pH and so conditions must be monitored carefully throughout the analysis.

    Various organic acids and amines were added to the IUC 18 extraction solution (5.1)4 and any colour development was monitored throughout the Cr VI determination procedure. No actual leaching of leather was performed. The test compounds were spiked into the extraction solution and the analysis was completed.

    The compounds tested to determine their potential to generate false positive were:
    • Organic acids
    • Acetic acid
    • Propionic acid
    • Butyric acid
    • Amines
    • Methylamine
    • Ethylamine

    Summary of tests

    In this work, the blank (7.4 IUC 18) refers to a 25ml volume containing 0.5ml of diphenylcarbazide solution (5.2), and 0.5ml of phosphoric acid (5.3) and extraction solution (5.1) to make 25ml volume.

    IUC 18 Method

    Blank with 0.2ml glacial acetic acid substituted for phosphoric acid
    Blank with 0.5g potassium propionate substituted for phosphoric acid
    Blank with 0.4ml 2,2 dimethyl butyric acid (98%) acid substituted for phosphoric acid
    Blank with 0.5ml butyric acid substituted for phosphoric acid
    Blank with 5g rancid butter (butyric acid)
    0.5ml diphenylcarbazide solution + 0.5ml butyric acid (99%)
    0.5ml diphenylcarbazide solution + 0.5g potassium propionate
    0.5ml diphenylcarbazide solution + 0.5ml glacial acetic acid
    0.5ml diphenylcarbazide solution + 0.5ml methylamine (36% solution in water)
    0.5ml diphenylcarbazide solution + 0.1g ethylamine hydrochloride (98%)
    Blank containing 20ppm Cr VI
    Blank containing 20ppm Cr VI with 0.2ml butyric acid
    Blank containing 20ppm Cr VI with 0.2g potassium propionate
    Blank containing 20ppm Cr VI with 0.2ml methylamine (36% solution in water)
    Blank containing 20ppm Cr VI with 0.2g ethylamine hydrochloride (98%)
    Blank containing 20ppm Cr VI with 0.2ml glacial acetic acid

    Bartlett and James chromium oxidation test method5

    Diphenylcarbazide Cr VI test5 + 0.2ml glacial acetic acid
    Diphenylcarbazide Cr VI test + 0.2g potassium propionate
    Diphenylcarbazide Cr VI test + 0.2ml butyric acid (99%)
    Diphenylcarbazide Cr VI test + 0.2ml methylamine (36% solution in water)
    Diphenylcarbazide Cr VI test + 0.2g ethylamine hydrochloride (98%)


    Test 3 showed that potassium propionate forms a pink colour with 1,5-diphenylcarbazide, at pH8, but when the pH is lowered to 4.4 with the IUC 18 standard amount of phosphoric acid, the colour dissipates.

    Tests 7-11 showed that in the presence of the diphenylcarbazide solution alone, all of the organic acids and amines tested give a pink colour reaction with the 1,5-diphenylcarbazide. However with the addition of the extraction solution and phosphoric acid, as per the IUC18 method, the colour dissipates.

    The tests were repeated with a 1ml spike of 1,000ppm chromium VI standard solution (K2Cr2O7) in the extraction solutions added prior to the addition of the diphenylcarbazide and phosphoric acid solutions. The spike gave a final concentration of 20ppm in the test solution. The absorbance at 540nm was no greater than the control in any of the samples with organic acid or amine spikes; hence no oxidation of the 1,5-diphenylcarbazide occurred as a result of the organic acids or amines. In all cases, the pH of the solutions was adjusted with phosphoric acid to match the pH of the blank solution containing 20ppm of Cr VI (test 13).

    Tests 19-23 used the Bartlett and James chromium oxidation test5: no false positives were observed with any of the tested reagents.

    Conclusion and discussion

    None of the organic acids or amines tested generated false positives using the IUC 18 standard method.

    Tests did show that the diphenylcarbazide solution (5.2) reacted with the organic acids and amines resulting in colour development.

    However, the colour was pH dependent and when the extraction solution (5.1) or phosphoric acid solution (5.3) was added, the pink/red colour dissipated in all cases.

    The Kallenberger and Hernandez paper is correct in stating that simple organic acids and amines react with diphenylcarbazide to produce a pink colour. However, it has been found that if the IUC 18 standard method is adhered to, organic acids and amines will not produce false positives in Cr VI determinations.

    These findings do not alter the fact that concerns about Cr VI content in leather are unjustified as discussed by Cory6. As recently stated by Long7, the criteria for setting limits in materials should be based on the risk to the manufacturer and consumer, and CEN BT 132 is currently considering the effect of Cr VI on the human body.

    Reports of Health-Based Soil Action Levels8 and case studies involving human exposure to Cr VI in soil and ground water9 put the relative toxicity of Cr III and VI into perspective. Cr VI is more toxic than Cr III but low levels can be tolerated and are not carcinogenic.

    The human studies showed that the gastrointestinal tract can reduce ingested Cr VI to Cr III at concentrations up to 10ppm Cr VI and soil concentrations of 1240ppm Cr VI do not elicit allergic contact dermatitis in over 99.9% of the general population. It is acknowledged that about 0.5% of the population is sensitive to chromium but chrome tanned leather has been worn for over 100 years and this sensitivity has been managed.


    (1) A J Long, N J Cory and C B Wood, Potential Chemical Mechanisms causing False Positive Results in Hexavalent Chromium Determination, J Soc Leather Tech Chem, 84, 74, 2000

    (2) W E Kallenberger and J F Hernandez, Mechanisms for false hexavalent chromium determinations in aqueous extracts from leather and soil, World Leather, December, 31-33, 2003

    (3) False Hexavalent Chrome Concentrations, Leather International, November, 17-18, 2003

    (4) Draft IUC Determination of Chromium VI Content, J So. Leather Techno. Chem, 86, 283, 2002

    (5) R Bartlett and B James, Behaviour of Chromium in Soils: III. Oxidation, Environ Qual, 8, 31-35, 1979

    (6) N J Cory, Environmental Constraints, JALCA, 97, 496, 2002

    (7) A Long, Chromium VI in Leather Updated, Leather International, November, 19-20, 2003

    (8) D M Proctor, E C Shay and P K Scott, J Soil Contamination, 6(6), 595, 1997

    (9) B L Finley and D J Paustenback, J Soil Contamination, 6(6), 649, 1997

    Created by:LANCEY, Ms. Raphaelle 01/11/2007 2:45:55 PM
    Modified by:LANCEY, Ms. Raphaelle 01/11/2007 2:45:55 PM

    No correlation between chromium (VI) in leather and chromium allergy - October 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 4:46:24 PM

    A high number of studies regarding hexavalent chromium and leather have been carried out during the past ten years. Most of the studies have been focused on the analytical method to determine hexavalent chromium in leather and especially the extraction process and the specificity of the method has been discussed. The question which has been raised is whether the results from the analytical methods can, in fact, actually determine the content of hexavalent chromium in the leather. These reports and studies will not be discussed in this paper.

    Furthermore, some research work has been carried out to determine which factors can provoke the formation of hexavalent chromium in leather and ways to prevent it. Here, the conclusions have been similar in most of the reports and several guidelines on how to avoid the formation of hexavalent chromium in leather have been published.

    The results from these studies have been valuable for the leather industry but it seems that we now have to go one step further in order to achieve greater progress. It is important to go back to the reason for analysing the eventual amount of hexavalent chromium in leather.

    The main reason for carrying out the analyses is that a limited number of people may develop chromium allergy from leather products. For example, it can be mentioned that there are around 200-300 new cases of chromium allergy in Denmark every year due to footwear.

    Although the number of new cases of chromium allergy is low, it is in the interest of the leather industry to reduce this number. The allergy is a big problem for the individual suffering from the allergy but, taking into consideration the number of cases of chromium allergy, we should not overestimate the problem.

    In 2002, Leather International presented the results from a study made by the author (Investigation of the content of Cr (VI) and Cr (III) in Leather Products on the Danish market). The Danish study was financed by the Danish EPA and showed that around 35% of the leather products on the Danish market contained hexavalent chromium.

    The Danish EPA decided to carry out additional studies in Denmark in order to find a correlation between the content of hexavalent chromium in leather and allergy. These studies were carried out by the National Allergy Research Centre for Chemical Substances in Consumer Products at Gentofte Hospital in Denmark.

    The research centre at Gentofte Hospital has a very high scientific reputation and is an institution of excellence. Data from the centre has been used regularly by the European Commission's advisory services to provide recommendations for protecting the consumer.

    The studies were mentioned in Leather International (p44, September 2002) and these have recently been finished. The results will mainly be published in scientific journals for dermatology and, hence, the results will mainly be spread to researchers in this field. The results are highly interesting and relevant for the leather sector and the main results from the study will be presented in this paper.

    Before going into the details of the study, some basic facts about allergy and chromium allergy in particular will be presented.

    Allergic contact dermatitis

    Allergic contact dermatitis (ACD) is an inflammatory skin condition caused by skin contact with sensitising molecules in the environment. ACD occurs when the immune system reacts to a substance (allergen). Examples of chemicals which can give allergic contact dermatitis are metals, biocides/preservatives, fragrance chemicals and dyes.

    The mechanism of ACD can be separated into two distinct phases: the sensitisation phase and the elicitation phase. The sensitisation phase includes the events following the first contact with the hapten (allergen) and is complete when the individual is sensitised and capable of giving an ACD reaction.

    The elicitation phase is initiated upon re-exposure of the same hapten to the skin and results in the clinical manifestations of ACD. The dose and time is much higher for the sensitisation phase compared with the elicitation phase (when the patient already has developed sensibility for the allergen).

    Today the sensitisation potential of a substance is investigated in animal models only, while the elicitation is normally determined by dose response studies using patch testing. Hence, the standard procedure for diagnosing allergic contact dermatitis (ACD) is patch testing.

    Patch testing is a way of identifying whether a substance that comes in contact with the skin causes inflammation of the skin. The test involves the application of various test substances to the skin under adhesive tape that is then left in place for 48 hours. The skin is then examined two, three and seven days later for any response.

    The trivalent and hexavalent oxidation state of chromium are sufficiently stable to act as haptens. The hexavalent chromium penetrates the skin to a larger extent than trivalent chromium since the latter binds to skin proteins, thereby becoming captured in the stratum corneum and epidermis.

    Furthermore, some studies in the past have shown that there is a greater skin barrier rejection of Cr (III) and that this may explain the difference in allergic potency between Cr (III) and Cr (VI). Haptens (allergens) must bind to proteins in order to obtain an allergic reaction. It is, therefore, believed that Cr (VI) becomes reduced to Cr (III) within the skin.

    It should be noted that trivalent chromium which is bound into the leather does not have any role in contact allergy. Only soluble chromium which can penetrate into the skin may play a role in chromium allergy. There is hence no relevance to analyse (or regulate) the total amount of chromium in leather in relation to avoidance of leather-induced chromium dermatitis.

    Finally, it should be noted that the investigations, which have been made in Denmark and will be described, have been carried out on patients who are chromium allergics.

    Studies at the National Allergy Research Centre, Denmark

    In the first study made by the National Allergy Research Centre, response studies (patch test with different concentrations of potential allergens) were performed in order to determine the minimum eliciting threshold (MET) concentration for Cr (III) and Cr (VI) in Cr (VI)-sensitive patients. A total of 18 chromium-allergic patients were patch-tested on the back with a dilution series of potassium chromate (Cr (VI) and chromium trichloride (Cr (III)).

    The study concluded that although Cr (VI) was confirmed as being the most potent hapten, Cr (III) also demonstrated a significant capacity to elicit allergic reactions. Most studies in the past have shown a significant difference between hexavalent chromium and trivalent chromium in relation to allergy. It should be once again noted that the investigations are made on patients who were existing chromium allergics.

    In the second study, the relationship between the content of Cr (VI) and soluble Cr (III) in leather and the ability of the leather to elicit eczema in chromium-allergic patients were investigated. This study is of high relevance for tanneries since it is the first study actually looking at the correlation between hexavalent chromium in leather and allergy.

    A group of 15 chromium-allergic patients with a history of foot dermatitis and leather exposure was exposed to a selection of 14 chromium and one vegetable-tanned (control) leather samples on the upper back. The leather was applied as small squares (4cm2) on the upper back using Scanpore tape. The content of hexavalent chromium in the leather samples was determined according to DIN 53314 and the soluble Cr (III) was determined by atomic absorption spectrometry in the DIN 53314 buffer. Five of the 14 chromium-tanned leather samples elicited an allergic reaction in at least one patient and four patients reacted to at least one leather sample. The results are shown in Table 1.

    As can be seen from Table 1, the leather sample eliciting a reaction in the highest number of patients was the one with the lowest content of Cr (VI) and soluble Cr (III). The leather samples with the highest concentration of Cr (VI) which were 16.9ppm and 15.5ppm did not cause any reaction.

    The conclusion from the clinical studies is: No relation was observed between the measured content of Cr (VI) and soluble Cr (III) in the leather and the elicitation of eczema (at the concentrations used in the studies).

    Discussion of results

    Using the DIN 53314 method, no relation was observed between the amount of Cr (VI) and soluble Cr (III) in leather and the elicitation of eczema. However, the study does not reject a connection between the content of Cr (VI) and soluble Cr (III) and the development of eczema. It simply demonstrates that the DIN 53314 method lacks the capacity to determine the relevant bioavailable pools of Cr (VI) and soluble Cr (III) in leather and, therefore, cannot be used for analysing the Cr (VI) content in relation to avoidance of leather-induced chromium dermatitis.

    Furthermore, it must be underlined that there is no direct evidence that the 'chemical agent' eliciting eczema is chromium. Leather contains many chemicals and, in theory, other chemical components may cause the observed dermatitis.

    It should also be mentioned that the relation between Cr (III) and other shoe-related allergens is unknown. There may be synergetic effects which are unknown so far. It is possible that the presence of other shoe allergies would increase the risk of developing chromium sensitivity. Thus the increased risk for foot dermatitis in the patients sensitive to chromium may be caused by shoe allergens and not by chromium.

    Shoe allergens (eg rubber chemicals or adhesive chemicals) may have affected the skin barrier and thereby promoted the development of chromium allergy. It is possible that the leather manufacturer and the use of chromium has been unjustifiably blamed for shoe allergy and instead other allergic components present in shoes may play a bigger role.

    Based on the results from the study, it must be concluded that the DIN 53314 method (and other available analytical methods on the market) lacks the capacity to determine the bioavailable pools of Cr (VI) and soluble Cr (III) in leather and cannot be used for analysing the Cr (VI) content in relation to avoidance of leather-induced chromium allergy. New methods have to be developed to take into consideration the true exposure situation.

    The final recommendation to the leather industry is to continue to avoid the formation of hexavalent chromium in leather and furthermore to ensure that the trivalent chromium is properly fixed so there is no free chromium in the leather.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 4:46:24 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 4:46:24 PM

    Prevention of chrome (VI) formation by improving the tannery processes - October 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 4:54:37 PM

    The Chrom6less Project

    The Chrom6less Project (Prevention of chromium (VI) formation by improving the tannery processes) is a two-year-long research programme (2003-2005) that has involved eleven partners from three European countries.

    The project has been funded by the European Commission in the thematic programme: 'Competitive and sustainable growth'.

    The aim of the project has been to identify the operations of skin/hide transformation into leather that facilitate or hinder the transformation of Cr (III) to Cr (VI), to determine the most suitable protective measures which prevent this oxidation and to establish the most suitable manufacturing conditions to allow the production of leathers that are free of hexavalent chromium, even during their useful life in contact with environmental agents such as heat and light.

    The participants in this project are convinced that tanning with trivalent chromium salts, with an appropriate management of the amounts offered, as much as the recovery of the residual chromium in the waste baths is the best state-of-the-art tanning procedure. They are interested in demonstrating that by means of a rational and systematic study, the problem of chromium (VI) is not a relevant complication and its formation at trace levels may be prevented to fulfil the requirements of the European Eco-label and the German Law.

    The project consortium is summarised in Table 1.

    The problem of the analytical methodology

    The procedure DIN 53314, like the former version of the method IUC 18, presents significant difficulties analysing dyed skins/leathers. False positives of chromium (VI) have been reported as a result of the interference of some dyes.

    The project partners were concerned about inconsistent and incoherent results from several chromium (VI) analyses and about reports in several media about high percentages of leathers containing chromium (VI). Therefore, they have supported the goal of establishing an analytical methodology which provides reproducible results that may be free of interferences.

    An inter-laboratory study was developed during the Chrom6less Project Exploratory Award. Several coloured leathers were analysed applying the draft of the new analytical procedure proposed by the CEN/TC Committee.

    All participants in the study analysed the same leathers, each with five replications. The study revealed good behaviour and provided reproducible results between laboratories. Also it was observed that leather colour was no longer a problem. Moreover, the participating laboratories showed themselves to be capable of implementing the new analytical procedure1,2.

    The first result of the project, and one of the most relevant, has been the validation of the |analytical methodology after hundreds of analyses, without interference problems. Now it has become clear that the determination of chromium (VI) in all kinds of leather can be carried out with great confidence, regardless of their colour.

    Nowadays, this methodology has been approved by the EU as an official Technical Specification and has been named CEN/TS 14495. The detection limit of the method is 10mg/kg, higher than other methods due to the required dilutions. The International Union of Leather Technologists' and Chemists' Societies has also updated the former IUC 18 Standard, adopting an equivalent procedure3.

    Of course, the CEN/TS 14495 has been applied during the project. Results have been expressed on dry weight. The humidity was previously determined in a different piece of sample than the one used for the analysis. All of the measures were at least duplicated.

    Good practices and concrete recommendations to avoid chromium (VI) formation

    In the tanning process

    Recommendation: Ask the chemical suppliers, mainly from outside the European Union, for a certificate guaranteeing the absence of hexavalent chromium in tanning agents.

    In the neutralising process

    Recommendation: Finish wet processes at acidic pHs, between 3.5 and 4, by means of formic acid fixation. Carry out a final washing.

    In the retanning process

    Recommendation: Use between 1-3% of vegetable tannin extract to provide antioxidant protection.

    In the dyeing process

    Recommendation: Avoid the use of ammonia prior to dyeing.

    In the fatliquoring process

    Recommendation: Assess the influence of fatliquoring agents of natural origin on the formation of Cr (VI) before use. In leather where it is not possible to apply a vegetable extract due to the colour change, a 1:1 mixture of a phenolic and an amine antioxidant should be used due to its protective capacity.

    In the finishing stage

    Recommendation: Avoid the use of yellow and orange inorganic pigments completely.

    In the analytical laboratories

    Recommendation: Require the laboratories to implement the new official method CEN/TS 14495 for the determination of chromium (VI) in samples of dyed leather.


    The first and possibly the main result of the project has been the verification of the success of the new CEN/TS 14495 method. After hundreds of analyses carried out in the laboratories of the participating members, no problems or interferences were detected.

    Thus, it is now possible to confidently determine the chromium (VI) content in all kinds of leather, regardless of their colour.

    The Chrom6less Project has shown that most of the skins/leathers do not contain hexavalent chromium.

    In more than 99% of the skins/leathers produced and analysed in this European Project, not subjected to accelerated ageing treatments, Cr (VI) was not detectable. In the few remaining cases in which hexavalent chromium was detected, the reasons were identified. Currently, according to the results of this project, it is easy to avoid these remaining cases in industrial production, by applying the previously explained recommendations.

    This means that the estimations and predictions of a high percentage of skins/leathers containing Cr (VI), published a short time ago, were overestimated owing probably to the use of data obtained by a methodology yielding inexact results. The application of the protective measures developed in the project allows leather to resist the effect of ageing without the formation of Cr (VI).

    It was established that an unsuitable fatliquoring agent can facilitate the formation of hexavalent chromium in skins/leathers subjected to an accelerated ageing. It was also demonstrated that a suitable retanning process can afford lasting antioxidant protection.

    One percent of vegetable tanning agent (on wet-blue weight), applied in the retanning process, is sufficient to meet the most demanding specifications.

    In order to ensure that the leather is resistant to an accelerated ageing process without forming Cr (VI), the protection conferred by this 1% will be sufficient for many skins/leathers.

    But for other kinds of leather, it will be necessary to increase the offer of vegetable extract to 2-3% depending on the fatliquoring agents, the thickness of the skin/hide, the dyeing process and the type of finishing.

    The protection obtained by the 1:1 mixture of a phenolic antioxidant and an amine antioxidant is suitable for leather without finishing in which vegetable extract is inapplicable because of the modification of the colour produced. The use of yellow and orange inorganic pigments must be completely avoided.


    The authors are grateful to the European Commission for the financial support given through the Chrom6less Project (CRAFT 1999-71638).

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 4:54:37 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 4:54:37 PM

    TA.1.7. - What's new in leather chemicals?

    Alkylphenol ethoxylates: A European problem? - July 2004
    Contributed by: Leather International magazine
    Last updated: 06/11/2007 3:19:43 PM

    New legislation has reduced the limits on use of nonylphenol and nonylphenol ethoxylates if they are capable of being discharged as effluent after use. Dr Brigitte Wegner, BASF AG, Ludwigshafen, looks at the consequences for tanneries in Europe and the rest of the world.


    Alkylphenol ethoxylates (APEO) are nonionic surfactants which can be components of leather chemicals. The 26th amendment to European Council Directive 76/769/EEC relating to restrictions on the marketing and use of certain dangerous substances and preparations reduces the limit on nonylphenol and nonylphenol ethoxylates for use in a wide variety of applications from 1% to 0.1%. This article deals with the consequences of this new legislation on the tanneries in Europe and worldwide, as well as with the alternatives for APEO-containing products offered by the chemical industry.


    The 26th amendment to European Council Directive 76/769/EEC relating to restrictions on the marketing and use of certain dangerous substances and preparations was published in June 20031.

    This legislation, effective from January 17, 2005, reduces the limit of nonylphenol and nonylphenol ethoxylates contained in preparations for use in a wide variety of applications from 1% to 0.1% if they are capable of being discharged as effluent after use. Nonylphenol ethoxylates (NPEO) are the most important products in this important group of nonionic surfactants, the alkylphenol ethoxylates (APEO).

    What are the consequences of this new legislation for tanneries in Europe and other parts of the world? The following issues need to be addressed in order to answer this question.

    What are alkylphenol ethoxylates, how are they produced and what are their special features?

    Alkylphenol ethoxylates, APEO for short, are nonionic surfactants. They differ from cationic and anionic surfactants in that their performance is not affected by the presence of electrolytes, and this allows them to be employed over a wide pH range.

    Alkylphenol ethoxylates are manufactured by causing alkylphenol to react with ethylene oxide. The length of the hydrophobic alkyl chain and the hydrophilic polyglycol chain can be varied in order to adapt them to a wide range of applications.

    Their performance can be tailored according to the particular applications for which they are intended. Apart from being very effective surfactants, alkylphenol ethoxylates are also attractively priced.

    Alkylphenol is readily available compared with other feedstocks used to manufacture nonionic surfactants. Alkylphenol ethoxylates have been synthesised for many years in large-scale plants and the production processes have been completely optimised.

    Table 1:

    Figure 1:

    Table 2:

    In which branches of industry are they used?

    Alkylphenol ethoxylates are highly effective wetting agents and emulsifiers and they can be employed in all situations in which hydrophilic and hydrophobic substances have to be brought together. Their applications range from detergents and cleaners through to textile auxiliaries, paper auxiliaries and pesticide formulations.

    They are used in the metal industry, in emulsion polymerisation processes and as stabilisers in the manufacture of paints and coatings. They are also employed in leather auxiliaries. The most important applications for APEO are listed in Table 3.

    Table 3:

    Why is the use of nonylphenol and nonylphenol ethoxylates so tightly regulated?

    Around 700,000 tonnes of nonylphenol ethoxylates are sold on the market each year, which makes them the most significant products in the APEO group of nonionic surfactants. The latest amendment to the EU Directive has consequences for all of the products in this group.

    Because alkylphenol ethoxylates are nonionic, they can still be present in the wastewater when it is discharged into the effluent treatment plant after they have fulfilled their purpose. When they are treated biologically at first the polyglycol chain is broken down step-wise and in the end among other products the alkylphenols can be formed again. These degradation products do not readily break down in the environment when they are discharged from effluent treatment plants.

    The nonylphenol that is formed as a degradation product of NPEO is toxic to aquatic organisms2, as can be seen from Table 4.

    Figure 2:

    Table 4:

    The EU, therefore, decided to make a risk assessment for nonylphenol and nonylphenol ethoxylates to assess their effects on the environment. This was done by estimating the amounts of nonylphenol and its derivatives that are consumed in all their various different applications.

    The concentration of nonylphenol in the environment was estimated on the basis of a variety of figures, such as the consumption data, wastewater emissions and removal rates from wastewater. The aquatic toxicity of nonylphenol was also determined in laboratory experiments.

    The risk assessment indicated that the use of nonylphenol and nonylphenol ethoxylates at current levels poses a risk for the environment. The result was that EU Directive 76/769/EEC was amended in order to severely restrict the use of nonylphenol and its ethoxylates.

    This was the culmination of more than thirty years of research into the potential risk posed by nonylphenol and nonylphenol ethoxylates. The history of the restrictions that have been placed on nonylphenol and its ethoxylates is summarised in Table 5.

    Table 5:

    Table 6:

    What are the applications for APEO in the leather industry?

    Products that contain alkylphenol ethoxylates can be employed in the leather industry in all applications in which hydrophobic substances such as fats, oils or waxes have to be emulsified in aqueous media. They can be employed in finishing auxiliaries and, to a lesser extent, in fatliquors and water repellents. However, their main application in the leather industry is to remove the natural fat from the skin in the beamhouse on account of their excellent surface activity.

    Beamhouse - degreasing

    The natural fat contained in the skin has to be removed as thoroughly as possible for high-quality leather to be obtained. The penetration and distribution of the chemicals that are applied to the leather later on in the process can be affected if the fat is not removed, and this is visible in the finished leather in the form of greasy spots and stains.

    Various different degreasing processes can be employed. Pelts with a relatively low natural fat content, such as cattle hides, are usually degreased in an aqueous float at the beamhouse stage. Very greasy pelts such as certain types of sheepskin can be degreased with organic solvents in a separate process. The changes to EU Directive 76/769/EEC only affect aqueous degreasing processes in which the grease is emulsified in the float. In future, products that contain more than 0.1% NPEO may no longer be used in Europe.

    However, this amendment does not affect degreasing processes for sheepskins, in which the organic matter is completely removed from the wastewater before it is treated in a biological effluent treatment plant.

    Up until now, the most common practice has been to degrease skins in water with surfactants such as NPEO or fatty alcohol ethoxylates. Nonylphenol ethoxylates have been employed as degreasing agents on account of their better performance and their superior cost effectiveness.

    The problems that had been experienced with APEO over the years prompted BASF to investigate the mechanisms involved in degreasing in greater detail.

    The degreasing process was modelled in cooperation with the University of Cologne3 and various products were screened to assess their degreasing performance.

    The result of this development work was Eusapon OD, an innovative degreasing agent for leather and wool/hair-on skins.

    Like APEO, Eusapon OD is a nonionic surfactant and it shares all the positive features displayed by this class of products. The advantage of Eusapon OD over products based on APEO is that it is readily biodegradable and environmentally friendly.

    The practical performance of Eusapon OD was tested in comparative trials with standard NPEO surfactants and it was shown to be much more effective for degreasing pickled cattle hides.

    Studies have also shown that Eusapon OD can be used to degrease all types of raw stock from cattle hides through to pig skin, goat skin and sheepskin, and it can also be used for wool and hair-on finished skins.

    Sheepskins are not yellowish after they have been degreased with Eusapon OD, but have an exceptionally clean, pale wool, which can be dyed to very brilliant shades.

    As well as being a very effective degreasing agent, Eusapon OD is also easier to handle because it is easier to dissolve in water and it forms less foam than nonylphenol ethoxylates3.

    Figure 3:

    Table 7:

    Table 8:

    Post-tanning treatment - fatliquors and water repellents

    After the leather has been tanned, the next step is to replace the fat that has been removed from the leather in order to make it soft and supple. Natural and synthetic waxes and oils can be used in fatliquors, depending on the type of effect that is required.

    Modern water repellents generally contain polysiloxanes. Both of these groups of products are normally supplied in the form of emulsions, and alkylphenol ethoxylates are still used to emulsify and stabilise emulsions of this type.

    The majority of fatliquors and water repellents are self-emulsifying to some extent.

    The fat contained in fatliquors is treated by a variety of chemical reactions such as sulfation, sulfonation or phosphation in order to insert hydrophilic groups into the hydrophobic fat.

    This increases its affinity for the leather and also makes it self-emulsifying.

    However, additional emulsifiers are often added to improve the stability of emulsions and to allow them to withstand long periods in storage and variations in temperature etc.

    Nevertheless, alkylphenol ethoxylates do not necessarily have to be used here and all of the products in the global BASF range of Lipoderm and Lipamin fatliquors and Densodrin water repellents are free of APEO.

    Post-tanning treatment - wetting back

    Surfactants have to be added to the float when crust is wetted back in order to enable the hydrophobic leather to be wetted quickly and efficiently. APEO-based wetting agents are not an appropriate choice, especially if ammonia needs to be eliminated from the process for ecological reasons. The alternative is to use surfactants such as Eusapon OD, which is based on a long-chain alcohol.


    The most complex aspect of this problem is the use of APEO in finishing. As can be seen from Table 10, alkylphenol ethoxylates can be employed as emulsifiers in a wide variety of finishing products.

    Table 9:

    Table 10:

    Acrylic binders can contain APEO because alkylphenol ethoxylates are employed as stabilisers in the emulsion polymerisation process that is used to manufacture these products. Alkylphenol ethoxylates are no longer employed in the production of any of the acrylic binders in the global BASF range of Corial binders.

    For many years, the tendency in the finishing sector has been to replace solvent-based products with water-based products for reasons of industrial hygiene and ecology. This often makes it necessary to emulsify hydrophobic matter in water.

    Alkylphenol ethoxylates were often used as emulsifiers in the past but there are plenty of other alternatives and the need to reformulate products often makes it possible to make more wide-ranging improvements. For instance, Lepton Wax WN was introduced last year as an APEO-free alternative to Lepton Wax WA, which was well established as a handle improver and as an additive for enhancing the Taber abrasion resistance of finishes. The new Lepton Wax WN has a VOC content of <1%, which means that it is virtually free of volatile organic compounds and fulfils the highest ecological standards.

    Modern finishing binders and auxiliaries can nowadays be manufactured without APEO having to be used4.

    How is the use of APEO regarded in countries outside the EU?

    Although no legislation restricting the use of nonylphenol and nonylphenol ethoxylates has yet been introduced in many countries outside the European Union, these products are increasingly coming under critical scrutiny as is shown by Table 12.

    Table 11:

    Table 12:

    Table 13:

    An additional factor is that companies and retailers with international operations are inclined to adopt the standards set by European environmental legislation in their specifications within the framework of Responsible Care and Sustainable Development. This puts them under pressure to use only products that are free of APEO.

    This voluntary approach takes effect more quickly than compulsory measures imposed by legislation and it affects all tanneries, including those in countries outside the EU, who are active internationally and wish to remain competitive.

    What are the consequences for the leather industry?

    The level of interdependence that now exists between tanneries and manufacturers of leathergoods will ensure that new legal restrictions within the EU will have worldwide repercussions. Restrictions on the use of nonylphenol and nonylphenol ethoxylates will affect the entire leather industry, not just Europe.

    However, well-timed development programmes by the chemical suppliers to the leather industry will make sure that a complete range of products free of APEO will be available when the new legislation comes into force on January 17, 2005. These products can replace the products that contain APEO completely and without restrictions and they may even perform much better than existing products, as shown by the example of Eusapon OD, or offer additional ecological advantages as in the case of Lepton Wax WN.


    1. Official Journal of the European Union 17.07.2003.

    2. http://ecb.jrc.it/existing-chemicals/

    3. Paper presented by Gunter Pabst, ALCA Congress, June 2003. Gunther Pabst, Philippe Lamalle, International Tannery, October 2003: p172.

    4. Stefan Adams, Leather International, August 2003; p40. Stefan Adams, Leder & Häute Markt 6, 2003; p33

    Created by:LANCEY, Ms. Raphaelle 06/11/2007 3:10:52 PM
    Modified by:LANCEY, Ms. Raphaelle 06/11/2007 3:19:43 PM

    A new approach to the degreasing process - August 2005
    Contributed by: Leather International magazine
    Last updated: 19/09/2008 10:40:32 AM

    The amount and composition of natural fat in skins varies according to the species. In this paper the composition of the natural fat and the percentage removed as a function of the pretreatment has been investigated by V Candar and Y Eryasa, Cognis Kimya AS Istanbul Organize Deri San Bolgesi, Tuzla-Istanbul, Türkiye. A version of this paper was presented at the IULTCS Congress in Florence, Italy, by Volkan Candar.


    To determine how natural fat varies between different species and how pretreatments affect grease removal, an analysis was developed by the Cognis leather department. This test screened the effectiveness and performance of widely used emulsifying agents in relation to extracted natural fats from skins. After numerous analyses, it was observed that the performance of surfactants varies substantially from skin to skin, depending on the difference of the natural fat composition of the skin. This approach allows the appropriate type of emulsifying agent to be used in the most effective way for the degreasing process. Using this technique, sheepskins from different sources were screened to consider the effects of pretreatment, since this may influence the effectiveness of the degreasing. The structural changes in the fat composition as influenced by the chemicals and process parameters such as soaking, liming and pickling were also investigated. The results of the small scales tests were then verified on degreasing processes in laboratory drums and subsequently in tannery trials. Through this work, a totally new approach to the degreasing process was built up.

    Degreasing is one of the most important processing steps since the consequences of inadequate degreasing can result in irreversible damage to the finished leather. This process step is usually carried out using an appropriate emulsifier with some degree of biodegradability, after bating or in some cases after pickling or depickling, in a short float and under mild temperature conditions.

    Different aspects of the process have been widely investigated, taking into account the efficiency of the degreasing in terms of remaining natural fat, its distribution, concerning chemistry and process parameters 1,2,3,4,5, including the use of enzymatic degreasing 6,7.

    The ecological aspects of degreasing have also been investigated6,7,8,9,10,11,13,14, and with the necessity for more ecofriendly degreasing agents, alkylpolyglycosides (APG) were presented in London at the IULTCS 1997 centenary congress8. In this work, surfactants with different degrees of polymerisation and alkyl chain lengths were used to degrease English domestic and New Zealand sheepskins.

    Natural fat

    Given that the natural fat from one skin source varies to another (Table 1), both by its composition and structure, it would seem reasonable to assume that varying the surfactant to suit the skins would be a suitable way to degrease properly. The emulsifying capacity of emulsifiers varies with respect to the fat composition, which itself is a function of the carbon chain length, amount and nature of triglycerides, phospholipid content, the existence, or absence, of waxes and their nature.

    The differences in the chemical composition of fat from Turkish sheep and English domestic sheep were also investigated using TLC techniques. The Turkish fat contains less triglyceride and phospholipids; is lower in cholesterol and exempt of monoglycerides. However, it is more viscous, while the English origin skin's fat has more triglycerides, cholesterol and monoglycerides.

    The premise that degreasing agents act differently depending on the fat composition was first tested in 1998 on four pigskins from different sources by using the same degreasing agent and increasing the concentration. The results of this work are shown in Tables 2 and 3, where the related carbon chain distribution of concerning extracted pig fats is given without considering eventual waxes and phospholipids, which may surely differ as well. These results encouraged us to review different chemical structures, which are or probably will be used in degreasing through the newly-developed simulation test method.

    This method consists firstly of the extracting the skin's natural fat, then the standard mixing in a different ratio of fat/emulsifying chemical, using a micromixer and finally defining and ranking the type and the stability of the fat/emulsifying chemical-water system emulsion for predefined periods of time.

    Simulation tests showed that regarding skin origins, different surfactants/degreasing agents act differently as a function of origin. For instance, one degreasing agent proved very efficient on English domestic skin but performed poorly on Entrefino. These results demonstrate clearly a justification of the above-mentioned premise and create a basic conceptual change for the traditional approach to degreasing. This allows an a priori identification of the most suitable degreasing agent for each skin/hide origin and, hence, the most efficient and economic way of degreasing.

    For the simulation tests various skins and hides, both raw and pretreated were selected.

    For the sheepskin degreasing assessment, English Domestic, American, Norwegian, South African, Azerbaijani, Spanish Entrefino and Merinos, Australian, Libyan, Turkish and French Lechal raw skins were investigated in their raw and pickled forms considering, in some cases, the time left in pickle as well.

    The following chemical moieties were used:

    1. Non-ionic surfactants based on fatty alcohol alkoxylates with various fatty alcohol chain lengths and degrees of alkoxylation; fatty acid ethoxylates; various fatty alcohol chain lengths and degrees of ethoxylation; APGs with various alkyl chain/polymerisation degree ratios

    2. Anionic surfactants based on fatty alcohol sulfates; fatty alcohol ethersulfates; sulfurised fatty alcohol esters and hemiesters and their ethoxylates

    3. Pseudocationic nitrogenated surfactants

    Simulation test

    A simulation method for investigating the efficiency of different chemical structures and their combination for revealing probable synergetic effects on the degreasing capability on different natural fats was developed. This method consisted of Soxhlet dichloromethane/hexane extraction of the natural fat from the skin, hide or pelt powdered and then dried, taking care of the denaturation of the material.

    After evaporating the solvent, the fat was separated into two parts and the first part analysed for physical and chemical characterisation, while the second part was examined according to the simulation test. Different fat/emulsifier ratios were first prepared and analysed fixing all other parameters. A micromixer has been used to carry out the simulation test in order to create a water in oil (W/O) system of the natural fat first, excluding the influence of emulsifying style on the test results. W/O emulsions were then inverted to an oil in water emulsion using distilled water to a fixed volume and the emulsion was observed for fat separation at various times.

    Salt water, simulating pickle media, was also used for some of the trials in a comparative manner. These observations were ranked from 0-10, 0 corresponding to the non-emulsifying ability and 10, a 24-hour stable emulsion. All emulsions were evaluated according to this ranking.


    As a first step, the degreasing effect of selected surfactants was investigated, firstly on American, English domestic and Turkish origins. These trials showed that with the varying chemical structures the emulsion ability of the natural fat varied according to the differences in their composition.

    For example, surfactant K2 shows very high efficiency on Turkish skins but was less effective on American, while K12 is efficient on American but not to the same degree on Turkish. Surprisingly K10 was effective to some extent on American and English domestic but showed no effectiveness at all on Turkish origin natural fat.

    Following this preliminary study, reselected surfactants were investigated using various skin origins including from raw and pickle sources. It became apparent that changes in structure greatly affected the emulsifying ability of the surfactant.

    This was especially apparent in the case of linear long-chain medium alkoxylate and long-chain non-linear ethoxylate, while medium chain ethoxylate surfactant shows more regular efficiency, although its efficiency differed only slightly from one origin to another.

    On the other hand, Turkish, South African, Australian and Libyan sources presented more variability with regards to emulsion stability.

    The small-scale trial results suggest that the chemistry of the surfactant is important in determining the release of fat from skins, and that this is also dependent on the source of the skin. These findings form the basis for a new approach in defining the most suitable degreasing agent for a given tannery, which aims to produce a given article from a defined raw material. The simulation test results were verified on lab scale degreasing trials using specially designed products. Trials were carried out using the result of the simulation tests where first single products were applied and then mixtures of products added to determine probable synergy in order to economise the degreasing process.

    Tannery trials

    This new degreasing concept was successfully applied in some Turkish tanneries. Raw material of the participating tannery was first tested through the simulation test using the Cognis product portfolio. Defined best performing product(s) were then applied to the production of the tannery. Tannery application results are shown in Table 4. In this step of the study, at least ten samples were tested according to IUC4 and results are shown as median of random selected samples. In the table, standard deviations are also given.


    This study has demonstrated that each skin/hide origin comprising particular pretreatment applied has to be degreased precisely according to the analysis by the newly developed simulation technique which can indicate the most effective degreasing agent and/or suitable mixture of them.

    By using this study, it has been revealed certain degreasing agents are not to be used for some skin/hide sources. Using this approach, it is possible to signify an a priori degreasing agent and reduce the risk of leaving excess natural fat in the skins/hides.

    This study also showed it is possible to find a degreasing agent less dependent on origins. Hence the most appropriate, more economic and safer degreasing agents using the New Degreasing Concept are offered to the tanners as a beneficial tool.


    The authors thank Prof Meral Birbir, Faculty of Art and Sciences, microbiology division and Prof Ayse Ogan, Faculty of Art and Sciences, chemistry division, for their support on differentiation of natural fats using TLC techniques.

    Created by:LANCEY, Ms. Raphaelle 19/09/2008 10:40:32 AM
    Modified by:LANCEY, Ms. Raphaelle 19/09/2008 10:40:32 AM

    Analysing dangerous substances in liquid or solid form - July 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 3:51:52 PM

    An increasingly important issue in the leather industry currently is the ever-growing raft of regulations which lay down just what ingredients are permissible in all manufacturing processes and what level is acceptable in the finished article. Dr Humbert said that today's companies are increasingly aware of the importance of the environment.

    The leather sector is confronted by the problems of environmental protection and the lawful constraints are increasingly strict and all encompassing. Until the beginning of the nineties, only the basic parameters of wastewater (COD, BOD, pH etc) were followed and controlled.

    Since then, the situation has developed considerably with requests for monitoring parameters such as PCP (pentachlorophenol), PAH (polycyclic aromatic hydrocarbons) and many other organic micropollutants and the list is steadily increasing. The last stage of this process has been the publication of the European directive (2000/60/CE) [1] which lays down a common policy for wastewater.

    The behaviour of consumers has also been evolving. Durability was the prevalent argument but the nineties saw requests for greater technical performance. Since then, major medical crises have taken place (eg BSE) and now a real concern for the early 21st century consumer is that a product should be innocuous, not harmful. Products should not contain chemical substances (synthetic or natural), which could have a harmful effect on the health of the consumer.

    The toxic, mutagenic, carcinogenic products were the first products which led the European Union to publish several Directives prohibiting or limiting the use of these chemical substances (Directive 99/51/CE [2] concerning pentachlorophenol, Directive 2002/61/CE [3] prohibiting the azo dyes etc).

    During recent years, leather testing laboratories have been required to develop new methods of chemical analysis and acquire the necessary tools to enable them to check the conformity of products compared with the new European directives. The chemistry laboratories of CTC [4] set up new analytical techniques: ICP/OES, ICP/MS, GC/MS, GC/ECD, HPLC/FLUORIMETRY HPLC/DAD etc. Methods were developed to analyse products as varied as: azo dyes, bromodiphenylated ethers, organotin compounds and multi extraction and analysis methods.

    Nowadays, much European legislation exists concerning leather and other materials used in the leather sector. These texts define the products (shoe, leather etc) the chemical substances and also the conditions of use (produced in contact with the skin etc).

    Table 1 gives a non exhaustive list of the chemical substances most usually required.

    Parent water directive

    Directive 2000/60/CE [1] of the European Parliament and the Council of October 23, 2000, established a framework for a common policy in the field of water, which was transcribed in French law on April 21, 2004. It aims to maintain or restore ecological and chemical quality, thus avoiding a deterioration of surface water and subsoil waters in Europe. The recent adoption of this directive establishes a framework for a common policy in the field and points out the orientations related to the good state of the watery ecosystems. It must be consistent with the objectives of water protection. A list of 'dangerous priority substances' was defined (see Table 2). The ultimate objective of the directive is the improvement of the quality of natural environments by the suppression of these substances.

    Identification as a dangerous priority substance reflects the intrinsically hazardous properties of a product and indicates that it is 'toxic, persistent and bioaccumulable'. The list drawn up by the European Directive refers to 33 substances (Table 2). In France, the Ministry for Ecology and Durable Development brought the European list up to 87 substances. In fact, a list of 132 substances constituted the reference frame.

    The MEDD wished to continue monitoring certain substances in the list of the 132 and add it to the list of 33.

    Image above: Samples are collected to determine the nature of waste.

    New extraction techniques

    In order to be able to cover such a variety of substances as those listed in Table 2, it was first necessary to develop new methods of preparation and extraction. This led CTC to invest in new apparatus such as:

    * distillation systems (PCP in leathers)

    * microwave (azo dye analysis, European project : AALARM, micro organic compounds in sludges, fat content in leather)

    * soxtec/soxhlet (phthalate in pvc, extraction of leather)

    * head space (COHV, BTEX)

    * thermodesorption

    New analytical technique GC/MS

    Gas chromatography coupled to a mass spectrometer (GC/MS) formed part of the analytical methods used during development. It made it possible to carry out the qualitative proportioning of aromatic amines, the quantitative proportioning of the organotin compounds, bromodiphenylated ether, phthalate and phenol. Mass spectrometry is an extremely significant detection technique which makes it possible to determine molecular structures.


    The High Performance Liquid Chromatography (HPLC) facilitates the analysis of very large molecules, of thermolabile or fluorescent compounds.

    In the study, this technique is used with a detection UV with the diode bar. The objective is to quantify the azo dyes or phenyl urea.

    This detector makes it possible either to vary the wavelengths or simultaneously, in order to record the absorbance, to cover several wavelengths. Thus, in addition to the recorded signal (chromatogram), this detector makes it possible to provide information which can be used to identify the required compound.

    Through tackling the various problems along the way, CTC have developed more and more 'expertise' and as a consequence have developed some analytical methods making it possible, for example, to find the cause of problems of odour or discolouration thanks to complex techniques such as fluorimetry, infra red and the head space analyses.

    Analysis development

    The challenge for CTC was to develop a powerful method in order to extract and analyse a maximum of compounds at the same time in order to limit the number of analyses and to reduce costs imposed on industrialists. The first step was to classify the various compounds according to their physicochemical properties and find a global analytical solution. Except for semi metals, it led to the determination of two types of family:

    * the semi volatile and non volatile compounds

    * volatile compounds

    Based on the methods already developed, the groups of micropollutants were split within these two large groups. Thereafter, it was necessary to anticipate which compounds could have a similar behaviour by taking into account chemical properties such as thermolability, volatility, stability in acid medium etc.

    Once the substances were identified, the objective was to determine the types of detection most suited to quantify the compounds while keeping in mind a multi residue logic. For this strategy of analysis (screening) followed by several tests, four groups were essential (Table 3).

    For certain groups, there are normative references concerning the preparation of the sample (groups IV and II). Nevertheless, for the volatile organic compounds, the optimisation of the analysis was necessary in order to separate the compounds concerned with the Parent Directive for Water.

    The analysis of organotin compounds had to be carried out several times to refine the quality of the analysis. And with regard to the analysis of the chloroalcanes C10, C13, the lack of reference involved the use of experimental designs in order to find a suitable method of preparation of the sample to discover the right analytical technique to use the second time.

    The last group of compounds was the one which required the most deliberation although normative references do exist for certain substances. Indeed, the difficulty of the multi residue approach was to find a preparation of the sample which was powerful enough, according to the chemical properties of the compounds (indeed the analysis gathers phenols, triazines, organochlorinated and phosphorated pesticides) and also provide a good quality of analysis.

    Then, further thought needed to be given on the preparation of the samples. The objective was to find a solvent combination allowing the extraction of the compounds concerned by very diverse chemical properties. The use of experimental designs made it possible, amongst other things, to vary this parameter, but also the pH and the quantity of solvent used according to the load of the matrix. This led to the choice of two different solvents used in acid media, basic and neutral and in quantities depending on the load of the matrix.

    To conclude, Table 4 gives a summary of the analytical strategy.

    As a result of this study, CTC now have a range of methods which make it possible to quantify a great number of substances potentially present in effluents. Following the adoption of Directive 2000/60/CE, the Ministry for Ecology and Durable Development (MEDD) set up a study in France involving 5,000 factory sites. The object of this work is to constitute an item zero which will make it possible in the future to better evaluate the evolution of the aquatic environments and their attack on the standards of optimal environmental quality.

    Obviously the activities of tanneries and megisseries were included in the list of the industrial facilities to be controlled. Thus CTC were brought in to analyse the wastewater of about thirty tanneries and to determine the presence of 87 different substances.

    * For each type of pollutant (metals, organic volatile compounds, organic non-volatile compounds), CTC determined:

    * the number of times that one could determine the presence of the substance considered in the effluents. This was then expressed in percentage terms compared with the other tanneries/megisseries tested

    * For each detected substance, they determined the concentration.

    Metal analysis

    The results observed for the analysis of metals (Figure 5) indicated that the three elements most found are chromium, copper and zinc and that, unsurprisingly, chromium is the element which is found in greatest quantity.

    Organic micro-pollutants

    On the level of the multi residue analysis concerning the various families of substances (Figure 6), it appears that certain phenols, naphthalene (aromatic hydrocarbon polycyclic) and diethylhexylphthalate (DEHP) are the compounds most found. These substances come primarily from the use of dyes (phenols and naphthalene) and also from the pvc channel (DEHP). Similarly, they are present in great quantity in the wastewater of the 30 tanneries.

    Lastly, the analysis of the volatile compounds (Figure 7) indicates the presence of aromatic compounds (benzene derivatives) and of tetrachloroethylene, the latter being present in the majority of cases.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 3:51:52 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 3:51:52 PM

    TA.1.8. - Drums

    Mechanical action considerations on tannery drums - September 2004
    Contributed by: Leather International magazine
    Last updated: 06/11/2007 6:01:16 PM

    Consideration of the general effects of mechanical action on tannery drums by Gustavo Defeo FSLTC, formerly with Genesis ecotec srl, Santa Croce sull'Arno, Pisa, Italy. The project is part of a wider EU-funded study which looks at different types of vessels and their influence on chemical penetration.


    This paper is part of the final reports for the Chempen project and analyses the factors influencing mechanical action, comparing different types of vessels in a context of possible chemical penetration variables. Partners of this European founded project are International Tanning (Ireland), BLC (UK), AIICA (Spain), University of Pisa (Italy), Tarnsjo Garveri AB (Sweden), Catalano Europea (Spain), Pere de Carme (Spain), Grad Chemicals (UK), and Genesis ecotec (Italy).

    Vessel's influence on mechanical action

    How can a vessel influence penetration? The first analysis shows that the main variables which may have an influence on mechanical action are:

    1. Type (a vessel may be a traditional drum, a Y drum, a square drum, a paddle, a mixer, Y disposition washing machines etc)

    2. Size (width and diameter)

    3. Speed

    4. Load

    5. Internal disposition (pegs, shelves, combined, and their size)

    6. Float recycling system (flux, turbulence, recycled volume)

    7. Material (wood, stainless steel, polypropylene)

    1. Type of vessel

    We will concentrate only on drums in this paper. We commonly find two types of drums: traditional drums (Figure 1) and Y type (Figure 2).

    Figure 1: Traditional drum

    Figure 2: Y type drum:

    Figure 3: Drum dimensions:

    Y type may be found as three-storey drums with a stationary float such as the washing machine type. Other vessel types include the square drum, mixer type such as Challenges, paddles and others.

    Each type of vessel will have a different mechanical action on leather, needing different float relations to run or move the skins. Because our partner tanneries just have traditional drums, we will concentrate on them, while making some references to Y type drums.

    2. Vessel size

    The fundamental parameters we must consider in drums are their internal diameter and length. Both parameters have obvious influence in the capacity of the vessels, while diameter will define a peripheral speed at a certain angular speed.

    3. Vessel speed

    The speed of a drum will define different types of mechanical action movement related to the maximum mechanical action speed (mmas).

    mmas is the speed at which the centrifugal effect of a given leather mass will be compensated for by its weight, falling from the highest part of the vessel. In Figure 4a, 4b, 4c, we can observe the mechanical effect at different proportions of the mmas.

    The figure 4a shows a drum running at 25% of the mmas where the centrifugal effect is very low and mostly the friction is between the pieces of leather with gentle action of pegs and shelves.

    Figure 4a: Drum speeds, running at 25% of their maximum mechanical action speeds (mmas):

    On Figure 4b, we can observe a drum running at 50% of its mmas where we notice a certain fall effect but not from the highest portion of the vessel.

    Figure 4b: Drum speeds, running at 50% of their maximum mechanical action speeds (mmas):

    Peg action at this speed will cause a mild bend and compression of the leather, while the low fall of the mass will generate a low hit compression.

    At 100% of the mmas (Figure 4c), the mass falls from the highest portion of the vessel, generating the maximal compression.

    Figure 4c: Drum speeds, running at 100% of their maximum mechanical action speeds (mmas):

    At this speed, the action of the pegs will also cause a strong compression by shock and bend.

    In case the speed is over 100% of the mmas, the centrifugal force will overpass the mass and so the mechanical action will be reduced with consequent energy waste.

    It is important to note that apart from the deformation strength with speed, the drum will achieve a certain hit frequency. In all these cases compression/release movement will generate a certain peristaltic pump effect that is one of the clue factors of penetration by mechanical action.

    Figure 5a: a short load (Figure 5a) will generate a reduced compression effect with respect to a big load (Figure 5b):

    Figure 5b:

    4. Vessel load

    The leather mass will be responsible for the falling hit which will generate the said compression/ release mechanism responsible for the peristaltic effect.

    Logically, the higher the leather mass, the higher the compression and peristaltic effect. This means that the compression pressure will be a combined speed/mass effect.

    5. Vessel's internal disposition

    A typical internal drum disposition may involve pegs, shelves (or a mix of pegs and shelves) and also big shelves as we can observe in Figure 6.

    Figure 6a: Internal disposition: pegs

    Figure 6b: Internal disposition: centre shelves:

    Figure 6c: Internal disposition: big shelves:

    Pegs and shelves help the leather mass to overcame inertia. Pegs are more indicated to avoid knots but their action is more aggressive.

    There are different types of pegs which may vary in size and shape, being from rounded cylindrical to flat shelf-like. Shelves have reduced tearing and deformation effects.

    Big shelves generate a high peristaltic and compression effect at low speeds, in which case mmas cannot be applied.

    As we saw in point 3, a combination of speed and internal disposition will generate a characteristic mechanical effect due to the contact hit, generating a certain compression/release effect.

    6. Float recycling system, recycled volume and flux

    The main effect involving a recycling system in penetration is the recycling volume which will define a float-in-vessel volume which will, of course, be different to the float-in-process volume.

    A low float-in-vessel volume will generate a higher chemical penetration due to a higher hit pressure and the consequent peristaltic and compression effect on the leather.

    A high float-in-vessel volume will produce an attenuation of the hit pressure, due to the Archimedes principle with a reduction of the peristaltic and compression effect, which will reduce penetration.

    A low float-in-process volume means a high concentration of the chemicals in respect to the water, propitiating penetration by an osmotic effect.

    Figure 7a: a short float (Figure 7a) will produce a high peristaltic and compression effect with respect to an intermediate (Figure 7b) or a high float (Figure 7c)

    Figure 7b:

    Figure 7c:

    7. Vessel construction material

    The most currently used materials for drums are wood, polypropylene and stainless steel.

    In our experience, we did not find any formal differences in penetration rates between these three types of material, just technical differences such as heat conductivity, abrasion and chemical resistance, and chemical absorption by the material itself.

    Regarding abrasion and chemicals absorption, stainless steel and polypropylene show more advantages than wood. Both are long lasting materials with a smooth surface and are easy to clean.

    With reference to thermal isolation, polypropylene is slightly more efficient than wood and much more efficient than stainless steel.

    Figure 8a: one of the most usual drum materials: wood (Iroko)

    Figure 8b: one of the most usual drum materials: polypropylene

    Figure 8c: one of the most usual drum materials: stainless steel

    8. Mechanical action calculation on traditional drums

    The movement of the drum with the help of pegs and shelves to overcame inertia will generate an increasingly high centrifugal effect on the leather mass causing it to fall from its higher part (mmas).

    Proportions of the mmas can be suggested for each step of the process, depending on the desired effect we want to obtain. For example, during chrome leather dyeing, we need a high hit of the leather mass so as to achieve the maximum compression and peristaltic effect of the leather to complete penetration in the shortest time.

    The opposite effect will occur during the beamhouse process and particularly with lime addition, where it is important to achieve a certain friction between the skins while, at the same time, limiting the abrasion by walls of the vessel.

    In Figure 9 we can observe a description of movements and speeds.

    Figure 9a: rotation

    Figure 9b: centrifugal effect

    Figure 9c: low mechanical action (suggested beamhouse)

    Figure 9d: mmas (suggested for chrome leather dyeing)

    One formula may be applied to calculate the percentage of the maximum mechanical action speed to define a mechanical parameter in a certain process or experience.

    This formula (Figure 10) may be applied only in pegs and short shelf configurations, because the big shelf drums work under a different logic: shelves in this case are not only a media to overcome inertia as was said before but a media for picking up the leather mass.

    In the formula, sD is the maximum mechanical action speed, wL is the weight of the load, L is the drum's internal width, and Δ the drum's internal diameter.

    Figure 10: mmas calculation:

    Applying this formula, we created the following graphic (Figure 11) which is a 3D representation showing the evolution of the percentages of the mmas, with respect to the volume occupied by the load and that of the mechanical efficiency. In this way we may calculate the optimal speeds for each vessel and the proportions of the mmas advisable for each process. In Figure 12, we may see the typical speed ranges for each of the traditional processes.

    Figure 11: 3d representation showing the evolution of the percentage of the mmas, in respect to the one of the volume occupied by the load and that of the mechanical efficiency

    Figure 12: Indicative speeds for different process:

    9. Mechanical properties of Y drums

    Y drums will have different movement logic as we can see in Figure 13.

    In this case, the mechanical action involves the following steps: a: rotation of the drum with lift action; b: first fall with very low/no float; c: rotation movement down; d: second fall with float involving rotation of the drum with lift action; e: rotation movement with friction.

    In the case of Y drums, the important measurement parameters to consider are, as we can see in Figure 14, the distance d, and as in a traditional drum the width and the loaded mass.

    Figure 13a: Y drum mechanical action: a rotation movement:


    Figure 13b: Y drum mechanical action: first fall:

    Figure 13c: Y drum mechanical action: a rotation movement:

    Figure 13d: Y drum mechanical action: second fall:

    Figure 13e: Y drum mechanical action: friction action:

    Figure 14a: Main parameter in the evaluation of Y drums mechanical effect:

    Figure 14b: Main parameter in the evaluation of Y drums mechanical effect:

    Italprogetti Engineering, Prof Jose Maria Adzet

    Created by:LANCEY, Ms. Raphaelle 06/11/2007 6:01:16 PM
    Modified by:LANCEY, Ms. Raphaelle 06/11/2007 6:01:16 PM

    TA. 1.9. - Beamhouse

    Reduced environmental loading key to survival - October 2004
    Contributed by: Leather International magazine
    Last updated: 07/11/2007 11:51:47 AM

    Beamhouse innovations that reduce the environmental loading for tanners are important if a tannery is to survive in the current economic climate. Dr Graham Lampard reports

    Learn to adapt and be prepared for change. Our world now changes faster than at any other time in history. The organisations most likely to survive are those capable of changing, adapting and not being afraid to seek help in doing so'1

    For organisations read tanneries and, specifically, the need to meet the plethora of environmental regulations that come from the regulatory authorities.

    Many tanners have failed to comply with the new rules and have closed; some have tried but the regulations have just been too tough; others have 'cheated' the system and moved production to areas of the world where the regulations are either less stringent or not policed as well. But, some tanneries have changed their production so that they can comply with the regulations.

    The first question to ask is where does most of the pollution in a tanning process come from? Table 1 gives figures for the environmental impact of leather production from beamhouse to tanning and it can clearly be seen that the former is the major contributor to pollution, accounting for about 75%.

    So, the aim of many researchers is how a tannery could operate a beamhouse operation with as little waste as possible; the dream being a zero waste tannery for the beamhouse operation with the sum of the processes utilised being commercially neutral. The challenge is to create savings that could be used to reinvest in new technologies - an iterative process leading to zero pollution.

    There are technologies around that could ensure 'zero' or reduced pollution loads. First, and one of the more obvious, would be to treat the solid wastes. As Leather International3 highlighted last year, tanneries such as Tanneries Nouvelles Pechdo, the French glove manufacturers, are looking at alternative revenue sources and saving costs.

    Nouvelles Pechdo produce approximately eight tons of solid waste a day from their fleshing operation. This represents 90% of the total solid waste produced in the tannery. The waste was sent to landfill as a category two material, which was more expensive to dispose of than typical household landfill.

    However, they installed a fat fuel burner unit. The waste fleshings are separated in fat and water by heating to 70ºC and the solid fat waste is combusted, while the water is directed back to the tannery effluent treatment plant.

    The burner works as a combustion system and not an incineration method and the latent heat produced is used to heat the water.

    Secondly, there is the use of fresh hides rather than salted, so reducing the total dissolved solids in wastewater, as Table 1 also shows. This is particularly important in countries where water is at a premium.

    However, the conundrum is that countries that have a poor water supply generally tend to have a poor infrastructure generally, have higher ambient temperatures and poor collection facilities; all of which are non-conducive to fresh hide/skin production.


    The tanner has three options for preservation depending where he is in the world:

    •  alternatives to salt

    •  salt-saving processes

    •  short-term preservation

    In hot climate countries such as India or most of Africa, drying either in the open air or in sheds is a real possibility. Indeed, many tanneries in India use the outside conditions to dry their wet-blue stock.

    Interestingly, the majority of the raw material seems to be wet-salted, presumably because the time needed to rehydrate air dried or sun dried stock can be inordinately long. Also, there can be problems of case hardening if the skin is dried too quickly.

    One of the obvious ways to reduce TDS is to remove the salt before it enters the float. This can be achieved by either desalting the hides and skins by hand or by using a mechanical desalting machine.4,5 This can be as basic as a rotating sieve in which the hides are placed. Rotating the drum expresses the salt through the holes.

    The salt could be reused, probably after washing and recrystallising. If the hide is not desalted, then the alternative is to collect the soak liquors and evaporate the water and collect the salt for reuse.

    The reduction in TDS can also be achieved by: • ammonium-free deliming, eg carbon dioxide, and bating

    • modifications of tanyard and wet finishing operations resulting in significant reductions of sulfate and chloride discharges

    •  the concentration and accelerated solar evaporation of (recycled) soak or other concentrated saline liquors

    •  the application of membrane technology for TDS removal either in separate streams or, in some cases, from the treated effluent

    •  the transport and discharge of saline waters into the sea and the reuse of treated effluent for irrigation of selected land plots planted with salinity resistant species

    'That salt, in spite of its inherent impact on the environment, is the most widely used preservative today shows how difficult it has been to find a suitable alternative', David Bailey commented in his 2003 JA Wilson lecture to the American Leather Chemists' Association.

    He said the only major change in practice in the last few thousand years was using brine curing instead of salt packs and this occurred less than half a century ago.

    Salt curing presents environmental challenges for the tanner and the packer that become more difficult to overcome as time goes on.

    Despite all of these shortcomings, no commercially acceptable alternatives have been put into use on a large scale. And Bailey has spent a large part of his career looking for alternatives.

    In many ways he was successful, but industry felt, and probably still feels, that salt is the easiest, cheapest, and best known preservative for hides.

    There are, of course, many alternatives and in the US these could include:

    •  using hides fresh, but unless the tannery is right on the doorstep, this is impractical. However, it may be possible for someone like Tyson to process through to the blue, but there are concerns about whether available markets make the monetary outlay realistic

    •  chilling hides, which is expensive, and needs infrastructure, but some of the costs could be offset by other uses of the hides, such as gelatine and collagen cases

    •  the possible use of chemical preservatives such as biocides, sulfite/acetic acid, and bacitracins, which are anti-bacterial peptides. In some small scale trials, these proved very effective against bacteria at room temperature. However, the work has been halted due to possible patent applications, Bailey noted with regret.

    The chemically-based one he seemed to like best was the mixture of sulfite and acetic acid, which he trialed in the late 60s. In a 30 day trial, hides were kept in a barrel at elevated temperatures and, when tanned, produced perfectly good leather. Bailey suggested the mechanism probably involves the release of sulfur dioxide, which acts as the preservative

    •  on an even simpler level, replacing sodium chloride with the potassium salt is something that could be put in place tomorrow. 'It's (KCl) a perfect copy with none of the environmental concerns.' Bailey cannot understand why this technology hasn't been developed further. He has done large scale trials and shown that KCl has no adverse effect on leather quality.

    •  another favourite, and one which may eventually become an industry standard, is irradiation. Having tried both gamma and electron beam irradiation, Bailey is convinced of the latter. Given that the FDA have approved e-beam irradiation of meat, it is just one step back to the hides. He pointed out that e-beam irradiation is not sterilisation of the hide, but that a small initial offer of bactericide ensures the hide is preserved long enough to transport and process6

    •  short-term preservation is another option. There were trials in South America to determine whether it was possible to put freshly killed hides that had been washed of blood and flesh into a lorry that had a revolving trailer, much like a cement mixer, containing dilute bactericides.7 The hides were impregnated with the solution while the lorry was going to its destination.

    Then, there is the application of enzymes in the beamhouse. Again, a huge amount of work has been done to reduce or remove the use of lime and sulfide in the unhairing process.

    However, the use of enzymes in the industry has been an enigma since the days of Wood and Turney at the beginning of the last century. They seem to offer cleaner production routes but then there are always problems of maintaining control of the reaction, temperature, pH, cost etc, or when they are used. During bating, for example, there is debate as to what they do or, indeed, whether they are needed at all.

    Leather area is primarily controlled by the structural proteins in the skin and their distribution and alignment within the grain, the corium and the flesh.

    It is the grain layer that has the most area to gain because it is composed of finer fibres, which are arranged in a convoluted manner. So, the use of alkali stable enzymes, while seemingly benefiting the tanner from the point of view of a cleaner production, must be carefully controlled if the leather is not to become too loose.

    Hair removal

    There are essentially two mechanisms of hair removal: breaking down the structure to a sufficient degree that it appears to dissolve (hair burning), or to detach the hair at its anchoring point in the follicle, so that at least part of the structure is apparently removed intact (hair saving).

    Again there have been many attempts to harness the latter, ranging from the commercially acceptable procedures such as 'Blair Hair' to the old methods of sweating and allowing bacteria to remove the wool from sheep, to more esoteric ideas involving chlorine dioxide and oxidative unhairing.8

    It has been shown9, through microscopy studies, that the morphology of hair structure, during typical hair burning with lime and sulfide, with and without the presence of proteolytic enzymes, demonstrated different rates of decomposition of the various components of hair: cuticle, cortex, medulla and root zone.

    The decomposition mechanism involves the dissolution of the cortex, the main constituent of the internal structure of the hair shaft.

    Whether or not the hair is cut prior to applying the hair burning agents, the cortex is dissolved, together with the medulla if there is a proteolytic enzyme present.

    Within the conditions and time period of typical hair burning, the outer part of the hair structure, the cuticle, is not dissolved. It may either remain intact, but collapse inwards, due to the hollowing mechanism, or it may break down into its scaly components: this is the scud of residual hair.

    The alternative approach with enzymes is to use them to detach the hair at its base, the basis of the hair saving techniques discussed above. However, use of proteolytic enzymes in such a procedure can lead to over opening up.

    A better idea is to attack the anchoring mechanism, the collagenous proteins of the basement membrane. This is something that was first suggested in the late 80s10 and the idea was updated to use dispase in enzymatic unhairing.

    Workers at BLC Leathersellers Research Company (BLCLRC) showed how the use of enzymatic removal of hair during beamhouse processing offered a suitable alternative, at least on the non-industrial scale, to destructive sulfide unhairing.

    One approach to enzymatic hair removal involved the degradation of the basement membrane to bring about epidermal sloughing with concomitant hair loosening.

    To be successful in this, the enzyme used must be able to degrade the basement membrane, type IV collagen in particular, while leaving the fibrous collagen of the dermis unaffected.

    The neutral protease dispase has such specificity and was consequently used in a series of studies to assess its effectiveness in hair removal from bovine hides.

    The enzyme caused loosening of the hair and associated hair loss, without damaging the fibrous collagen of the dermis.

    The elastin network of the grain layer was significantly affected by enzyme treatment, as were the physical properties of the resultant leather when compared with that of conventionally processed hides.

    Treating effluent

    Whatever beamhouse processes are used, the outcome will inevitably be effluent that needs to be disposed of.

    How this is done is a problem that is still being worked upon, but incineration and gasification are being considered, as was shown at the beginning of this article with the French tannery, Pechdo.

    Gasification is the conversion of a carbon containing solid fuel with a limited amount of oxidising at an increased temperature to produce a gaseous product consisting of hydrogen, carbon monoxide, methane, water, nitrogen and maybe ethane and propane, which can be used as a fuel to generate electricity and heat.

    Leather shavings or wastes such as sludge, trimmings, buffing dusts, and other leather waste materials are dried to 90% dry solids in a flash dryer and briquetted into a dense 'fuel'. The dryer heat requirement is fuelled by the syngas from the gasifier, thereby closing the loop and providing a self sustaining system. The dry fuel is pyrolysed or thermally degraded at temperatures above 250°C.

    So, the environmental impact of the beamhouse can be reduced by the potential use of fresh hides rather than salted, the application of enzymes to unhair, the replacement of ammoniacal salts in deliming by carbon dioxide, elimination of pickle salt etc, etc.

    The problem is that although individually each change has its merits, putting the whole lot together often leaves the tanner out of pocket, either through poorer quality leathers or extra costs through necessary upgrading of hardware.

    BLCLRC have an ongoing project to put such technologies together and to build a process capable of commercial exploitation by tanners.

    Once this process has been established and demonstrates a commercially acceptable quality, they will run a sequence of processes where the chemicals and water from the process are recycled.12


    1. Blakey, R J Soc Leather Technol Chem 2002 (6) 229

    2. Buljan J, IULTCS Congress 1995, Congress proceedings Paper 1 (figures revised)

    3. Ricker M, LEATHER International 2003 205 4738

    4. 'The scope for decreasing pollution load in leather processing' Ludvik J, Unido report US/RAS/92/120/11-51, August 2000

    5. 'Mass balance in leather processing' Buljan J et al, Unido report US/RAS/92/120 August 2000

    6. Bailey D, J Amer Leather Chem Assn 2003 98 (8) 308-319

    7. IULTCS Congress 1993, Brazil

    8. 'Hair-save unhairing methods in leather processing' Frendrup W, Unido report September 2000. US/RAS/92/120

    9. Addy V et al, IULTCS Congress Proceedings 2001, South Africa

    10. Stephens L, First Heidemann symposium, Philadelphia IULTCS Congress 1989

    11. Paul G et al, IULTCS Congress Proceedings 2001, South Africa

    12. BLC Annual Seminar 2003

    Created by:LANCEY, Ms. Raphaelle 07/11/2007 11:51:47 AM
    Modified by:LANCEY, Ms. Raphaelle 07/11/2007 11:51:47 AM

    Elastin in lamb pelts: its role in leather quality - March 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 11:12:56 AM


    Elastin is the major non-collagen fibrous protein present in lambskin after beamhouse processing, comprising 2.7% of the protein material in the grain (Keller, 1990).

    The role of elastin in lambskin processing has been the subject of particular interest as previous work has mostly been associated with the processing of bovine material (Webster et al, 1987, Alexander et al, 1991).

    However, the quantity and location of elastin in lambskin is different from that in hide and separate consideration should, therefore, be made in terms of processing to accommodate for these differences.

    There are unanswered questions about the role of elastin during mottle formation and the persistence of elastin during beamhouse processing through to pickle.

    Furthermore, some authors have claimed that elastin is not 'tanned' by basic chrome sulfate and that the removal of residual elastin from wet-blue material gave additional area gains (Addy et al, 2002, Rasmussen, 2002). The aim of this work is to outline some of the impacts of removing elastin from lamb pelts during beamhouse processing to enable more informed decisions when processing lambskins.

    Distribution in skin

    The amount of elastin throughout a skin was quantitatively measured in lambskin using high performance liquid chromatography (HPLC) (Lowe et al, 2000). Samples of measured area and ~2g wet weight were dried, defatted, and then hydrolysed in 6M HCl. Solid phase extraction was then carried out on the hydrolysate with cellulose to purify the elastin-specific amino acids desmosine and iso-desmosine. The amount of elastin was then determined by detection of desmosine at 268nm on the HPLC.

    It was determined that lambskin had a lower concentration of elastin than hide and that it was in highest concentration in the butt. Elastin content increased with the age of the animal. Interestingly, this is inversely correlated with the observed propensity to form growth lines during processing since new born lambs are more susceptible to growthiness compared with lambs which are more susceptible than sheep.

    The lower initial amount of elastin in lambskin could make the skin more susceptible to any possible adverse effects when a fraction is removed during beamhouse processing.

    Distribution and orientation of elastin in ovine skin

    Immunohistology has previously been used to investigate connective tissue components in bovine hides and kangaroo skins (Stephens et al, 1991). In the present work, samples of ovine skin were examined using immunohistology in order to investigate the location and orientation of elastin during beamhouse processing.

    Samples were prepared from lambskins at different stages during beamhouse processing including green skin, painted and pulled skin, and pickled pelt.

    Samples of skin were cut and marked for orientation to the spine and fixed in Bouin's fluid (saturated picric acid : acetic acid : water, 75:25:1) for 24 hours and then transferred to 70% ethanol to await processing. Samples were processed and embedded in paraffin wax. Sections were cut at 5mm thickness, floated on warm water, attached to glass slides and air-dried overnight before carrying out immunocytochemistry (ICC).

    The biotin-streptavidin detection system was used as follows:

    Sections were de-paraffinised and were then equilibrated in phosphate buffered saline (PBS) (0.01M), pH7.2 for 1 minute. The section was encircled with a PAP pen to create a fluid barrier to hold the reagents.
    Non-specific binding sites were then blocked by the addition of 1% bovine serum albumin (BSA) for 5 minutes followed by incubation in a humidity chamber for 1 hour. The sections were then drained and washed in three changes of PBS for 1 minute each.

    Anti-elastin antibodies (Sigma anti-elastin E4013 from mouse diluted 1:200 in BSA) were then added to the sections and then were incubated in a humidity chamber for 1 hour after which they were drained and washed in three changes of PBS. Biotinylated IgG (Amersham anti-mouse from sheep RPN1001 diluted 1:200 in BSA) was then added and the sections were incubated in a humidity chamber for 30 minutes.
    They were then drained and washed in three changes of PBS followed by biotin-streptavidin-peroxidase preformed complex (Amersham biotin-streptavidin- peroxidase RPN1.034 diluted 1:200 in BSA). Sections were then drained and washed in three changes of PBS then reacted in 3,3 diaminobenzidine (DAB) for approximately 3 minutes. The reaction was halted by immersion in PBS.

    The sections were rinsed in tap water and counter stained with Mayers haemalum for 1 minute, then blued in Scotts tap water for 2 minutes.

    Sections were then rinsed in tap water, dehydrated, cleared and mounted in DPX. The sections were examined under a light microscope at 20x to 40x magnification. The elastin appeared stained brown/black.
    The staining showed that most of the elastin appeared in the upper grain, where more appeared below the grain surface in the reticular layer and comparatively less elastin in the papillary layer immediately adjacent to the grain surface. Only small amounts of filamentous elastin associated with collagen bundles appeared to extend further down into the corium. In addition, it appeared that the orientation of elastic fibres depended on their location, with fibres appearing parallel to the spine in the lower grain and perpendicular to the spine in the upper grain.

    The elastin appeared to be relatively unaffected during the high pH stages of the lime sulfide beamhouse processing but its visibility became more pronounced after painting and pulling. After bating with a pancreatic bate, the elastin was less easily viewed using this technique. However, it was seen in the pickle that more elastin was removed from the layer of the grain immediately adjacent to the grain surface as compared with lower in the grain.

    Effect of varying elastin removal during beamhouse processing on leather quality

    Earlier investigations highlighted two important facts (Stone et al, 1982, Lowe, 1997). First, that high ionic strength solutions inhibit elastase activity without impacting on the general protease activity and second, that the presence of anionic surfactants enhances elastase activity. These two observations allowed bating trials to be conducted using the same enzyme but with modified elastase activity.


    Forty-eight lambskins from the same line of stock (Romney cross) were obtained. The skins were then processed through liming using the standard processes detailed in the appendix.

    The limed skins were washed and then delimed with CO2 without bating. After deliming, the skins were separated into four groups of twelve skins and bated with 0.01% of a high elastase bacterial bate with the following additives:

    (a) low elastase process - 2.5% NaCl

    (b) normal process - no additive

    (c) high elastase process - 0.1% sodium dodecyl sulfate

    (d) very high elastase process - 0.5% sodium dodecyl sulfate

    Each group was bated for 75 minutes at 35°C.

    Samples of bate liquor were taken for HPLC analysis of soluble elastin components as described above and the groups of skins were washed out of bating separately then recombined for pickling.

    The pickled skins were assessed for mottle, growth lines in the neck area (neckiness) and elastin content as described above and then processed together to dyed crust. Looseness was assessed with a 'break' scale where a score of 1 represented little or no looseness and a score of 5 represented a skin that was very loose (Lowe and Cooper, 1998).

    The results are illustrated in Figure 1, which shows the levels of elastin released during the bating process. This clearly illustrates the significant increase in groups with respect to the levels of elastin breakdown associated with increasing elastase activity. At the highest elastase level (0.5% SDS) over half of the elastin in the skin had been destroyed.

    Figure 2 shows the effect of elastin removal on the mottle and neckiness of the pickled pelts. Contrary to expectation, increasing the removal of elastin appeared to have led to increased growthiness of the pickled pelts. The expectation had been that the removal of elastin, which shrinks and becomes brittle upon drying, would improve the flatness of pickled pelts.

    In fact removing elastin exacerbated the mottling of skin during processing.

    The results suggest that residual elastin contributes positively to the character of the final ovine crust leather.

    For the very high elastin removal, there was a significant increase in looseness. However, there was no significant difference between the groups in tear strength, grain strength and softness.

    Effect of removal of elastin during beamhouse processing on area

    To investigate the impact of elastin removal on mottle formation and on area of sheepskins, a two level factorial experiment was carried out investigating a number of methods by which the removal of elastin can be altered during bating. The details for each factor investigated are given below.

    Bate type

    It is known that different bate types have different relative elastase activities even when normalised to the same general protease activity (Lowe, 1997). The bate types used were a pancreatic bate enzyme (Tanzyme, Tryptec Biochemicals) with low elastase activity and a bacterial bate (Pyrase 100L, Novozymes) which had high elastase activity as measured relative to the pancreatic enzyme. The pancreatic bate was adopted as the standard bate enzyme and was used to define the standard activity at an application rate of 0.1% w/v.

    Deliming method

    Altering the deliming from the use of ammonium salts to carbon dioxide increased the elastin removal during bating (Lowe, 1997). Ammonium sulfate (2% ) was used for the ammonium salt deliming and CO2 gas was injected into a recycled float stream until the pH reached 8.0 for CO2 deliming.

    Bate level

    It was expected that changing the amount of bate offered would increase both the general bate activity and the elastase activity during bating. The variables of bate treatment were carried out using 75% and 150% of the standard application rate of the pancreatic enzyme.

    Exposure time

    Changing the time of bate addition during the deliming/bating procedure may further expose any differences in the effects of general activity relative to elastase activity. The total deliming time given to the batches was 75 minutes.

    Bate was either added immediately (giving the full 75 minutes exposure time) or after delime had proceeded for 45 minutes (giving 30 minutes exposure time). The values used for the different factors are summarised in Table 1.

    Deliming was carried out separately on each of the 16 groups depending on the experimental factors. All batches were delimed for 75 minutes at 35°C and then washed 3 times with 100% water. All the groups were then combined for pickling.

    The amount of elastin remaining in the pickled pelts after processing was measured in stained histological sections using the scale illustrated in Table 2.

    Each sample was assessed on four different sections. In addition, each high/low pair (four pairs for each factor) were directly compared for remaining elastin.

    Elastin removal

    The results for the amount of elastin present in the pickled pelts were aggregated for each of the factors and the differences in the levels of elastin observed between high and low experimental levels was found to be significant at the 95% confidence level except for 'delime type' which was only significant to an 85% confidence level.

    In each case, the level of elastin removal was related to the level of elastase activity exposure as would be expected.

    * Higher bate levels gave more elastin removal

    * Longer exposure time to bate gave more elastin removal

    * CO2 deliming gave more elastin removal by comparison with ammonium salt deliming

    * The bacterial bate gave more elastin removal than the pancreatic bate even though the general activity of the two bates had been normalised Area For every individual skin the area was measured at the pulled slat stage and at the pickled pelt stage. All wet pelts were lightly slicked onto the area measuring table, avoiding any undue stretching out and measured electronically. During processing there was an overall increase in area. The 'pickle yield' was defined as the percentage increase in area between pickle and slat or:

    The average pickle yield found in this work was 15.5%. The data for all the skins were analysed together and the results for each of the main effects are plotted in Figure 3. The variable factor is plotted as 'lower' or 'higher' on the x-axis and the resulting pickle yield on the y-axis. The colours represent the different variables. Note, all main effects had a p value of less than 0.0005 giving a 99.95% confidence level.

    The following points were noted:

    * When the general level of bate activity was increased by increasing the bate offer, the area yield increased as would be expected

    * When bate was added part way through deliming, the area yield was reduced. This is probably because less complete bating was allowed to proceed. This again shows that increasing the duration of bating increased the area Neither of the above factors are elastase specific. Altering these factors merely altered the total general proteolytic activity during bating.

    * A major difference between the two bates used was the relative level of elastase activity Increasing elastase activity during bating by changing bates had a detrimental effect on the pickle area.

    It is important to note that the two bate types were applied at levels giving the same activity as measured using the hide powder azure test. The point is that at the same level of general activity against skin substance a greater removal of elastin during bating resulted in a reduction in area.

    * Using CO2 deliming gave less area than ammonium salt deliming. There are two possible reasons for this. The pH difference: at the beginning of deliming the pH of ammonium salt deliming is higher than the pH of CO2 deliming so it is possible that the relatively low pH during the beginning of CO2 deliming has moved conditions outside the optimal range for the two enzymes used and thereby reduced the total general activity of bating resulting in a slight reduction in area. Secondly, CO2 deliming results in a higher level of elastase activity during bating and again it can be seen that the conditions which caused more elastin removal correlated with reduced area.

    To summarise:

    * Increasing the general bating activity increased the area

    * Increasing the elastase activity relative to general activity reduced the area

    It appears as though two competing effects are occurring simultaneously. One effect involves the general activity of the bate, possibly a collagenase activity, which has the effect of relaxing and spreading out the skin and another effect involving the removal of elastin during bating which appears to be opposed to the relaxation and spreading out of the pickled pelt.

    It was noted above that excessive removal of elastin from ovine material can increase growthiness and mottle of the skin and it is possible that the elastase related effect, in which a reduction in area can be seen, is related to this effect. Perhaps, as elastin is removed during bating, growthiness increases which draws in the skin and reduces the area.

    Low elastase activity

    Overall the results show that removal of elastin from lambskin in the alkaline state, when the structure is under swelling tension, is likely to exacerbate mottle and looseness, demonstrating that application of elastase activity during alkaline process stages is contraindicated.

    Therefore, enzyme process stages such as bating or enzyme liming should be carried out with care and enzymes used should be of low elastase activity.

    Traditional ammonium salt deliming has a positive effect on retention of elastin by inhibiting undesirable elastase activity at this stage whereas CO2 deliming provides no inhibitory effect on elastase activity. While no area gains appear possible, through the use of a high elastase treatment prior to pickling some gains are possible on pickled product.

    Relationship between mottle in final crust leather and initial elastin content of green skin

    Up until now, the impact of elastin during the formation of mottle has been unclear. In order to examine the relationship between endogenous elastin and mottle observed in the crust leather, 120 lambskins from a variety of breeds were sampled and analysed for elastin content and processed to crust using the following procedure:

    Standard painting and liming process - standard delime, bate, and pickle process - aqueous degrease - chrome tannage - retannage to crust. The details of which can be found in the appendix.

    The crust leathers were then assessed for mottle by grading the skins against a fixed set of five representative samples with a range of degrees of mottle, where one represented a skin with low or no mottle and a score of five represented a skin with a high level of mottle.

    The results show a clear relationship between the quantity of elastin and the degree of mottle observed in the final crust leather with a significant negative correlation (>99.9% confidence). The greater the quantity of elastin that was initially present in the skin, the less was the propensity to form mottle during processing. Conversely skins which had less elastin present in the fresh material showed a greater chance of forming mottle during processing.

    Certain claims have been made recently about the effect of enzymatic removal of elastin after tanning has been carried out and the collagen has become cross-linked (Addy et al, 2002, Rasmussen, 2002).

    To investigate the impact of enzymatic elastin removal from ovine material after tanning, the following experiment was carried out:

    Twenty-four pickled pelt grain splits were obtained from a sheep pelt splitting operation. The grains were placed into three groups designated: controls, pickle and wet-blue, each having eight skins assigned.

    The three different groups were then converted through to crust using the following processes:


    Aqueous degrease - chrome
    tannage - retannage to crust


    Aqueous degrease - enzyme treatment - chrome tannage - retannage to crust


    Aqueous degrease - chrome tannage - enzyme treatment - retannage to crust

    The processes for aqueous degreasing, chrome tannage, and retannage to crust were the same for each of the three groups and are given in the appendix.

    The experimental bating treatments were the same whether applied before or after chrome tannage.

    The enzyme treatment involved 0.5% addition of enzyme product (Novocor AX, Novozymes) to 100% float at pH5.8 at 35°C for 90 minutes. Details of the experimental enzyme treatment are also given in the appendix.

    The areas were measured in the pickle, in the wet-blue, after neutralisation of the wet-blue, at the wet crust stage, and the dried crust after staking.

    The yield at each stage was measured as the percentage change in area after the process in question compared with the measurement taken prior to the process. Skin samples were taken in the pickle and in the wet-blue after the enzyme treatment. The samples were sectioned, stained and assessed for elastin removal.


    The data illustrated in Figure 4 show a significant improvement in wet-blue area yield in comparison with the controls when the enzyme treatment was applied to neutralised pickle grains (the pickle group). The increase in yield over the control pickles was 8+-3%.

    After chrome tanning and neutralisation, the third group (wet-blue) received the same enzyme treatment. The areas were then measured before and after neutralisation and treatment (Figure 5). Again, the yield was calculated as a percentage of the final wet-blue area on the original pickle area.

    When measured immediately after treatment, the results showed a 4% increase in area for wet-blue skins that received the enzyme treatment in comparison with the controls.

    All the skins were then processed to crust and the areas were then measured on the wet crust and again after toggle drying. The final overall area yields from pickled grain through to crust are illustrated in Figure 6.

    The results illustrated in Figure 6 show that the areas gained by application of the enzyme treatment to the neutralised pickle remained through to the finished crust, but when the enzyme treatment was applied to the neutralised wet-blue, there were no significant gains in crust area.

    In order to investigate the ability of this enzyme treatment to remove elastin from wet-blue material the levels of elastin were assessed microscopically for each pelt immediately prior to retannage. The results of this elastin assessment were not significant.


    Application of high elastase enzyme treatments to wet-blue ovine material provides no advantage to area in the final crust.

    An enzyme treatment to remove elastin from tanned material has previously been found to give area gains when applied to wet-blue bovine material.

    However, it was found in this work that while area gains were observed immediately after the enzyme processing of wet-blue lambskin, the area gain was temporary and was lost during the crusting process.

    However, when the enzyme treatment was applied to the neutralised pickle, this resulted in an increase in area that persisted through to the final dried crust as has been observed previously (Alexander et al, 1991).

    It is clear that the claimed beneficial effects of elastin removal obtained on cattle hides such as increased area and flatness are not fully reproducible on lambskins. There is also an accumulation of evidence that removal of elastin during early pelt processing is detrimental to the quality of the final leather because it induces looseness and increases mottle in the final product.


    Standard painting and liming process

    * Skins are painted with 300g/m2
    250g/l sodium sulfide flake
    50g/l hydrated lime
    5g/l pregelled starch
    Hold over night
    * Pull wool from skins and place in drum
    * 80% water
    Run 30 minutes
    Adjust sodium sulfide concentration to 2% w/v
    * Run overnight
    5 x 200% washes at 25°C for 20 minutes each
    Standard delime, bate and pickle process
    * 100% water at 35°C
    2% ammonium chloride
    0.05% pancreatic bate
    Run 75 minutes
    3 x 100% washes at 25°C for 20 minutes each
    * 90% water 2
    0% sodium chloride
    Run 10 minutes
    * 10% water
    2% sulfuric acid
    Run 3 hours
    Aqueous degrease
    * 100% water at 35°C
    4% non-ionic detergent
    Run 90 minutes
    * Drain
    5 x 100% washes at 25°C for 15 minutes each
    Chrome tannage
    * 100% water at 35°C
    8% common salt
    1% di-sodium phthalate
    1% formic acid
    Run 10 minutes
    * Add 5% chrome sulfate powder (33% basic)
    Run 30 minutes
    * Add 0.6% magnesium oxide
    Heat to 40°C
    Run overnight
    * Drain
    * 300% water at 25°C
    Run 10 minutes
    Retan to crust
    * 150% water at 25°C
    1% sodium formate
    0.4% sodium bicarbonate
    Run 45 minutes
    * 6% syntan
    Run 30 minutes
    * Drain
    * 300% water at 50°C
    Run 10 minutes
    * Drain
    * Add 100% water at 60°C
    0.2% ammonia solution (30% w/w)
    * Add 20% water at 25°C
    5% fatliquor
    0.5% formic acid (diluted 1:10 in water)
    Run 90 minutes
    * Drain
    1 x 300% washes at 25°C for 30 minutes
    Enzyme treatment
    * Drain float liquor
    * 100% water at 25°C
    Liquor adjusted to pH5.8 with
    1% sodium formate
    1% sodium bicarbonate
    Run 90 minutes
    * Drain
    * Add 100% water at 35°C
    0.5% Enzyme (Novocor AX, Novozymes)
    Run for 90 minutes
    * Drain
    * 2 x 150% washes at 25°C for 30 minutes each
    All percentages based on drained pickle weight.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 11:12:56 AM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 11:12:56 AM

    TA. 1.10. - Eco-friendly

    New approach for processing eco friendly garment leather - November 2004
    Contributed by: Leather International magazine
    Last updated: 25/03/2008 4:06:07 PM

    A physio-chemical investigation into a new approach for processing eco friendly garment leather and its comparison with a conventional process. By Nitai Basak, lecturer, and Sandeep Kinge, Btech (passed 2003), Department of Leather Technology, Dr B R Ambedkar, National Institute of Technology, Jalandhar-144011, India.

    Environmental safety is a major concern and with increasing demand from the western world for eco-friendly leather products, there are also much stronger norms/legislation for reducing the limits on harmful effluents coming from the leather industry. The concentration of chromium, sulfide and formaldehyde and the content of total solids, total dissolved solids, total suspended solids, BOD and COD in the effluent, should be as prescribed. Hence, new technologies have to be adopted to reduce the pollution and to make leather environment-friendly. There are various technologies available: one of which is applied in this project for the manufacture of eco-friendly garment leather. The analysis of the physio-chemical characteristics of the effluent is also carried out. This new technology is then compared with the conventional process to differentiate the magnitude of the parameters related to environmental concern.


    Untreated liquid effluent from the leather industry, adversely affects the streams, land and sewers where it is discharged. Apart from hair and suspended solids, the chemicals used (basic chromium salts, surfactants, ammonium salts, sodium sulfide, dyes, oils etc) also appear in the effluents.

    Animal proteins and fats exert a substantial amount of BOD value in the tannery effluent. Cr(VI) and arsenic compounds are toxic and other chemicals adversely affect water quality. Suspended solids such as hair, flesh and lime increase the turbidity of the land water, thereby reducing photosynthesising capabilities by the suspended microbial flora present in ground water.

    Ground water quality may be seriously affected if large quantities of dissolved solids such Cr, arsenic and chloride appear on land from liquid waste discharges.

    Fertility of the land is also adversely affected by wastewater from the tanning industry. If wastewater is discharged into municipal sewers, there is a possibility of blockages in the pipelines due to the formation of calcium carbonate from lime and the presence of hydrogen sulfide further accentuates the problem of wastewater handling.1

    Toxic effect of chrome on health

    Although the opinions regarding toxicity of Cr(III) and Cr(VI) vary, one thing is common. The accumulated concentration of Cr(VI) in the human body which crosses the limit, gives rise to the possibility of so many physiological disorders that chrome in general tends to be blamed and termed as toxic to human physiology. The toxicity of chrome falls into three types:

    1) Direct contamination of Cr(VI) with the skin or the soft portion of human glands (which may have transparent blood capillaries) may be absorbed directly. The continuous storage of Cr(VI) may cross the concentration level above which Cr(VI) is toxic to the human body.

    2) The inhalation of chrome in dust form may lead to an increase in the concentration of chrome in the lung or blood capillaries surrounding the pulmonary tubes and a toxic effect may be experienced.

    3) A chrome absorbed as Cr(III) if remaining in the digestive canals or stomach of humans may be oxidised by the pancreas. This could have a carcinogenic effect.

    In general the Cr(VI) compounds are corrosive under certain circumstances to the tissues of the human body. The chromic acid (H2CrO4) is particularly corrosive because of its strong oxidising capacity.

    Skin reactions are of two types:

    1) Cr Ulcers

    2) Cr Dermatitis

    3) On the Nasal Septum: The inhalation of chromic acid fumes or chromate dust lead to ulceration and perforation of the nasal septum apart from possibility of increasing concentration of Cr(VI) in the blood vessels and surrounding the pulmonary tubes.

    4) On respiratory tracts: as mentioned above the prolonged inhalation of chrome dust may result in a) congestion of the respiratory tract; b) congestion of larynx; c) chromic inflammation of lungs; d) chromic bronchitis and bronchopneumonia; e) asthma.

    Chrome may also act as a mutagen by directly changing the DNA bases. However, although the experiments with animals have shown the mutagenic capacity, there is no basis for its carcinogenic effect especially with respect to man. But since precaution is the best method of prevention, the presence of Cr(VI) is unacceptable in leather.

    But Cr(VI) is very mobile owing to its capacity to diffuse through biological membrane. Once it diffuses in tissue, it may be reduced to Cr(III) and thus participate in the specific bond formation as done by Cr(III).

    It is necessary to consider the total chrome combination of Cr(III) and Cr(VI) since the appearance of Cr(III) and Cr(VI) is governed by the degree of oxidation. Cr(III) is physiologically unstable and tends to form insoluble hydroxide in alkaline pH which accumulates in the spleen, liver and in bone marrow. However, at very low concentrations it is an essential component of many living organisms.

    Toxic effects of sulfide

    The toxicity threshold for fish daphnia and activated sludge with respect to S-2 are relatively low. The reduction properties of soluble sulfides exist even in the soil condition. When present on land, irrespective of oxygen rich or oxygen deprived environments, it affects the fertility of land (by reducing the oxygen holding capacity of land). If tannery waste is discharged onto a particular piece of land for one or two consecutive years it could cause the soil to become barren.

    The slightly acidic pH of land which is generally less than 7 (pK1 of H2S is 7.0) can form the toxic HS- (sulfurated hydrogen gas). The same is highly lethal at a concentration of 700 ppm giving an acute toxic effect at 100 ppm. The sulfide may cause serious corrosion since it is oxidised biologically to H2SO4 on the pipe walls.

    Toxic effects of dissolved salts

    The inhibition of enzymatic activity is visible in a range of 50 -100g/l of NaCl, as the usual concentration of the NaCl in tannery effluent is 5-10g/l. The problem due to dissolved salt is solvable but the storage of the effluent salts may cross that 50-100g/l limit and reduce the fertility of soil.

    Eco-Toxicity of nitrogenous compounds

    1) Organic nitrogen (ammoniacal nitrogen-reduced form)

    One gram of organic carbon requires approximately 2.6gm of oxygen for total oxidation whereas one gm of reduced nitrogen requires 4.1gm of oxygen; because of the higher oxygen demand, the reduced nitrogen or ammoniacal nitrogen has higher toxic effects. Ammonia is hydrolysable and can readily penetrate the tissues making it dangerous.

    2) Reduced nitrite-nitrates

    Action or receiving water along with significant phosphorous input, the presence of nitrite or nitrates varies the growth of algae. The growth of algae leads to a high rate of reduction in dissolved oxygen impregnated water because of the high rate of reduction of dissolved oxygen. The anaerobic condition prevails in the lower water layers such as phana (plant which can grow even at a very low concentration of dissolved oxygen).

    These conditions where all phana will quickly die are termed as 'eutrophication'. These lead to virtual death of any stagnant lake or water ponds. Although this process is reversible it takes a long time to revert to the initial stage or to get back to the equilibrium.

    Health hazards

    The conversion of NO3 to NO2 by bacteria whereby the NO2 may lead to other problems with drinking water.

    Methanoglobinemia, ie cyanosis of well water as it increases the concentration of ethane in the anaerobic condition in well water.

    Formation of nitrosoamine which is very carcinogenic for humans.

    Methanoglobinemia is the oxidised form of haemoglobins in blood; it may be produced due to the action of nitrites.


    Fe2+ ©Fe3+

    haemoglobin methano-globinemia

    It takes away from haemoglobin therefore reducing haemoglobin's ability to carry oxygen. This reaction easily takes place in infants since the pH is less acidic in the stomach of infants compared with adults. But if the reaction is in the first stage then the infant can be cured since the reaction is reversible.

    In order to reduce the ecological impact of leather production, new technologies were studied and applied, mainly in industrialised countries. These clean technologies can be applied at various stages of leather manufacture.

    Regarding chemicals used for effluent treatment, a more efficient use of existing chemicals and some new specialities which are biodegradable can be found in tanning operations.

    Eco-friendly technologies mainly include: harmless chemicals with better use, a decrease or prevention of waste materials, processes which reduce volume or waste product toxicity. However, leather production will always yield proteins in solution that should be eliminated through the most adapted resources.

    At the same time, the necessary production of important qualities of solid waste should be orientated towards easily upgradable refuse categories, ie non-chemically stabilised. In order to eliminate them as soon as possible in the fabric cycle, acceptable economic resources have to be found for their improvement.

    Finally, a search for new, less toxic products which can be used 100% has to be carried out. However, it must be pointed out that although they permit good or high reduction of the load in the effluent, some eco-friendly technologies aimed at reducing the liquid discharge cannot be used in the process line because they do not produce finished leather of the same characteristics as leather from a conventional process.

    Other technologies exist but they are still experimental and are reserved to specific use of the leather or are still difficult to operate. They need to be confirmed before application in leather manufacture.

    Raw material preservation

    The way to preserve raw hides and skins is of a great importance to obtain good quality leather at the final stage but it is also significant regarding salt and organic pollution generated during the soaking stage when hides and skins are washed.

    Several possibilities are available to partially or totally eliminate the salinity and collect organic pollution at an early stage. It is difficult to remove the salinity of the effluents as the technologies applied use costly equipment. In several countries, salt pollution is strongly restricted in order to protect the drinking water.

    The eco-friendly technologies available for raw material preservation are:

    * Treatment of fresh or chilled hides and skins
    * Partial salt elimination
    * Preservation with biocides


    Nowadays, the first phase of the tanning process is frequently speeded up by using enzymatic products that can be considered less toxic than sulfide. In other respects, the use of less harmful antiseptics will reduce the overall toxicity of the waste while preventing excessively rapid bacterial growth.

    Most of these products are more expensive than PCP (up to five times more) and may not have the same long-lasting effect.

    The new technologies are clearly less toxic than some products currently used such as phenyl mercury acetate, trichlorophenate, pentachlorophenol. The banning of PCP in leather, shoes and leathergoods imported by Germany has accelerated the withdrawal of these products in Asian and South American countries.

    Unhairing - liming

    The unhairing-liming operation is undoubtedly the largest contributor to the net pollution for tanneries. Conventionally, mixing the hides with lime and sodium sulfide leads to residual floats containing 55% of suspended solids, 55% of COD, 70% of BOD5, 40% of nitrogen and 76% of the toxicity of tannery effluent.

    The eco-friendly technologies available are:

    * Enzymatic treatment
    * Hair saving unhairing-liming methods
    * Direct recycling of liming floats
    * Splitting limed hides
    * CO2 deliming
    * Weak acid deliming

    Much research has been carried out into enzymatic treatment: dehairing and pilot programmes established with regard to the partial or even total replacement of sodium sulfide in the unhairing liming process.

    Today, except for small skins that are processed through sweating, the use of enzymatic products is mainly a partial substitution of sodium sulfide. On-site tests have yielded widely varying results that could not justify full-scale industrial use. A keratin-selective enzyme that does not attack collagen has yet to be found; such a process could result in a 30% to 50% reduction in pollution for this phase of tannery process.

    Hair brings about an important discharge load of COD and nitrogen, and recovery systems enabling eliminating from the treatment float before dissolution have been proposed. Residual hair can be used, however, for fertilization and composting.

    It is useful to mention the use of weak acid deliming operations (lactic acid, acetic acid etc), but their cost limits their application to specific cases. This cost is 50-100% greater than the conventional scheme, although the application rate is not more than 0.5 to 1% of the pelt weight.

    With the recycling of pickling floats, for the same reasons that lead to a lowering of the quantity of salts discharged during soaking, the pickling phase is now more strictly controlled. An earlier limitation of the float volume to 50-60%, led to a reduction of the amount of sodium chloride used in this stage of the process.

    Today, recycling of pickling float is common practice in many tanneries to reduce the salt pollution. After collection, the used float is sieved and its acidity (mainly from formic and sulfuric acids) is controlled in the laboratory. After readjustment to initial pH value, the float is reused for the following cycle. In practice, salt savings are about 80% and reduced acid consumption is estimated at 25%, although more formic acid is saved than sulfuric acid.

    Tanning operations

    Chromium tanning salts are used today in 90% of tanning processes. Only the trivalent form is used for tanning operations and this chemical cannot be replaced, except for special purposes, to give the same quality of leather. If its concentration in waste exceeds an acceptable level, it strongly limits any possibility of upgrading, or disposing of the waste at an acceptable cost.

    Therefore, today, the primary objective is the best possible use of chrome as this substance remains irreplaceable. The operations that precede the actual tanning have an influence on the chrome salt behaviour on the hide, and clean technologies exist for pickling operations.

    The other technologies available are:

    * Wet-white preparation
    * Recycling of pickling floats
    * Direct recycling of chrome tanning floats
    * Two stage recycling of tanning floats
    * Recycling after precipitation
    * Tanning products that improve the exhaustion rate
    * Other mineral tanning
    * Improvements in tanning equipment.

    Wet-white production

    In order to limit the amount of chrome containing wastes obtained after tanning (mainly splits and shavings), these operations need to be carried out earlier in the tanning process.

    The splitting of limed hides, in spite of its reduced precision, has several advantages. Shaving, which increases skin temperature up to 65-70°C, appears possible only once pretanning has already taken place. The use of aluminium salts as well as glutaraldehyde, zirconium, titanium, magnesium, on their own or combined with dialdehyde-based synthetic tanning agents, makes it possible to split and shave the leather of which tanning and character are perfectly reversible.

    In spite of the obvious advantages of such technology (good valorisation of pretanned waste, possibility of sorting before tanning, and improvement in surface yield), certain factors limit the diffusion of such a process. Current retanning and dyeing processes have to be somewhat adapted, as they react differently with aluminium pretanned leather.

    Retanning-dyeing-fatliquoring chemicals: today, Eco-friendly technologies suitable for this production cycle are principally based on the products used; especially dye and pigments. Chromium (VI), lead and cadmium salts can still be found in some types of older dyes and pigments.

    Some azo-dyes containing carcinogenic amino-compounds such as benzidine, have to be banned from tannery use.

    For re-tanning based on Cr(III), the same problem encountered with tanning arises. In some cases, the concentration of this element in the discharge is equivalent. Good practices should lead to an elimination of this kind of retan, or a selective recovery circuit, but not a recycling system in the process itself.

    Fatliquoring oils used in the tannery are often composed with chlorinated alkane sulfonates and fatty acid methyl ester sulfonates that are now questionable because of the organic halogen quantities they can generate.

    As a result of the regulation on absorbable organic halogens AOX, the chlorinated fatliquoring products will be replaced. Various substitutes are on the market to satisfy new laws in this field.


    Raw material used: cow calf skins
    Number of pieces: 11
    Average size: 4 sq ft


    Authority of Dr B R Ambedkar National Institute of Technology (Deemed University) Jalandhar for providing all kind of facilities for carrying out this research and correspondence for publication.

    CLRI, RCED, Jalandhar, for providing all sorts of facilities for carrying out the sample trial and using the testing facilities there.

    All the distributors of different leather chemicals companies in and around Jalandhar for providing sample chemicals to carry out the trials.

    Created by:LANCEY, Ms. Raphaelle 25/03/2008 4:05:30 PM
    Modified by:LANCEY, Ms. Raphaelle 25/03/2008 4:06:07 PM

    TA. 1.11. - Colour Measurement

    Identifying colour accurately - January/February 2005
    Contributed by: Leather International magazine
    Last updated: 25/03/2008 4:58:17 PM

    'The textile and apparel supply chain has $34 billion in waste from its current processes. Product design and development account for 20% of that figure.' According to Hau L Lee, Professor of Operations Management at the Graduate School Of Business at Stanford University (June 2002): 'Colour is identified as the largest factor impeding any real improvements here'.

    Communicating colour

    How would you describe the colour of this rose? Would you says its yellow, sort of lemon yellow or maybe a bright canary yellow?

    Your perception and interpretation of colour are highly subjective. Eye fatigue, age and other physiological factors can influence your colour perception. But even without such physical considerations, each observer interprets colour based on personal references. Each person also verbally defines an object's colour differently. As a result, objectively communicating a particular colour to someone without some type of standard is difficult. There must also be a way to compare one colour to the next with accuracy. The solution is a measuring instrument that explicitly identifies a colour. That is, an instrument that differentiates a colour from all others and assigns it a numeric value.

    Ways to measure colour

    Today the most commonly used instruments for measuring colour are spectrophotometers. Spectro technology measures reflected or transmitted light at many points on the visual spectrum, which results in a curve. Since the curve of each colour is as unique as a signature or fingerprint, the curve is an excellent tool for identifying, specifying and matching colour. The following information can help you to understand which type of instrument is the best choice for specific applications:


    Spherically based instruments have played a major role in formulation systems for nearly 50 years. Most are capable of including the 'specular component' (gloss) while measuring. By opening a small trap door in the sphere, the 'specular component' is excluded from the measurement.

    In most cases, databases for colour formulation are more accurate when this component is a part of the measurement. Spheres are also the instrument of choice when the sample is textured, rough, or irregular or approaches the brilliance of a first-surface mirror. Tanneries would all be likely to select spheres as the right tool for the job.

    0/45 (or 45/0)

    No instrument 'sees' colour more like the human eye than the 0/45. This is simply because a viewer does everything in his or her power to exclude the 'specular component' (gloss) when judging colour. When we look at pictures in a glossy magazine, we arrange ourselves so that the gloss does not reflect back to the eye. A 0/45 instrument, more effectively than any other, will remove gloss from the measurement and measure the appearance of the sample exactly as the human eye would see it. This type of unit is typically used in printing.


    In the past ten or so years, carmakers have experimented with special effect colours. They use special additives such as mica, pearlescent materials, ground up seashells, microscopically coated coloured pigments and interference pigments to produce different colours at different angles of view. Large and expensive goniometers were traditionally used to measure these colours until X-Rite introduced a battery-powered, hand-held, multi-angle instrument.

    X-Rite portable multi-angle instruments

    are used by most auto makers and their colourant supply chain, worldwide.

    Attributes of colour

    Each colour has its own distinct appearance, based on three elements: hue, chroma and value (lightness). By describing a colour using these three attributes, you can accurately identify a particular colour and distinguish it from any other.


    When asked to identify the colour of an object, you'll most likely speak first of its hue. Quite simply, hue is how we perceive an object's colour- red, orange, green, blue etc. Presented as a wheel or circle of colour there is a continuum of colour from one hue to the next so that if you were to mix blue and green paints, you would get blue-green. Add yellow to green for yellow-green, and so on.


    Chroma describes the vividness or dullness of a colour; in other words, how close the colour is to either gray or the pure hue. For example, think of the appearance of a tomato and a radish. The red of the tomato is vivid, while the radish appears duller. Chroma changes as we move from the centre to the perimeter. Colours in the centre are gray (dull) and become more saturated (vivid) as they move toward the perimeter. Chroma is also known as saturation.


    The luminous intensity of a colour - ie, its degree of lightness - is called its value. Colours can be classified as light or dark when comparing their value. For example, when a tomato and a radish are placed side by side, the red of the tomato appears to be much lighter. In contrast, the radish has a darker red value.

    Scales for measuring colour

    The Munsell Scale

    Hue, saturation and lightness demonstrate that visible colour is three-dimensional. These attributes provide three co-ordinates that can be used to 'map' visible colour in a 'colour space'. The early 20th Century artist Albert H Munsell - creator of the Munsell Colour Charts - is credited as a pioneer of intuitive three-dimensional colour space descriptions. There are many different types of colour spaces that are based on or resemble Munsell's designs.

    Over the last century many different scales of measuring colour have been developed including:

    * The CIE Colour Systems
    * CIELAB (L*a*b*)
    * CIELCH (L*C*H0)
    * CMC and CIE94 Equation

    (Further details on these scales are detailed in the Understanding Colour Communications book).

    To obtain these values, we must understand how they are calculated. There are many different colours as there are many different object surfaces and each object affects light in its own unique way.

    As stated earlier, our eyes need three things to see colour: a light source, an object and an observer/processor. The same must be true for instruments to see colour. Colour measurement instruments receive colour the same way our eyes do, by gathering and filtering the wavelengths of light reflected from an object. The instrument perceives the reflected light wavelengths as numeric values. These values are recorded as points across the visible spectrum and are called spectral data. Spectral data is represented as a spectral curve. This curve is the colour's fingerprint.

    Measured spectral data has a couple of advantages in that it is both device and illuminant independent.

    * Spectral data measures the composition of light reflected from an object before it is interpreted by a viewer or device.

    * Different light sources appear differently when they are reflected from an object because they contain different amounts of the spectrum at each wavelength. However, the object always absorbs and reflects the same percentage of each wavelength, regardless of amount. Spectral data is a measurement of this percentage.

    So the two components of colour that change with every viewing condition - the light source and the viewer or device - are 'bypassed' and the ever stable properties of the object's surface are measured instead.

    Detecting metamerism

    Another advantage of spectral data is its ability to predict the effects of different light sources on an object's appearance. As mentioned earlier, different light sources have their own compositions of wavelengths, which in turn are affected by the object in different ways. For example have you ever matched a pair of socks and trousers under fluorescent department store lighting and then, later, discovered that they do not match as well under your home's incandescent lighting? This phenomenon is called metamerism. 

    Colour control

    Colour control - or process control - is critical to achieving a consistent, quality colour throughout an entire batch, across different shifts or between different batches of materials. Any system of measurement requires a repeatable set of standard scales.

    Colour tolerances

    Verification between colour specifications and actual colour results is achieved by using tolerances that are based on numeric colour measurement data. Colour tolerancing involves comparing the measurements of several colour samples (the colour output) to the data of a known colour standard (the specification or input). Then, the 'closeness' of the samples to the standard is determined. If a sample's measured data is not close enough to the desired standard value, it is unacceptable and adjustments to the process or equipment may be required.

    The amount of closeness between two colours can be calculated using a variety of colour tolerancing methods. CMC tolerancing was developed by the Colour Measurement Committee of the Society of Dyers and Colourists in Great Britain and became public domain in 1988.

    The CMC calculation mathematically defines an ellipsoid around the standard colour with semi-axis corresponding to hue, chroma and lightness. The ellipsoid represents the volume of acceptable colour and automatically varies in size and shape depending on the position of the colour in colour space.

    The figure below shows the variation of the ellipsoids throughout colour space. The ellipsoids in the orange area of the colour space are longer and narrower that the broader and rounder ones in the green area. This size and shape of the ellipsoids also change as the colour varies in chroma and/or lightness.

    Although no colour tolerancing system is perfect, the CMC equation represents a 95% agreement with visual colour differences as our eyes see them.

    Integrated colour - throughout the supply chain

    The instrumentation and communication of colour data is as important as the colour data itself. Throughout the supply chain, different suppliers may use different processes and equipment for colour formulation and quality assurance, making compatibility an essential component. X-Rite products are designed for integration and compatibility throughout the supply chain. For example a large installation may use integrated, networked colour formulation and quality assurance software, such as X-RiteColourMaster, and several X-Rite sphere instruments throughout the shop. A small supplier with X-Rite QA-Master I installed on a single computer and one SP62 spectrophotometer will be compatible with the larger installation. Colour control is required in a wide variety of applications, in varied scopes. This is why X-Rite offers the following process solutions:

    Colour formulation and quality assurance

    From basic quality assurance functions to the most sophisticated colour formulation needs, X-RiteColour Master software, combined with X-Rite instruments, provides the ultimate flexibility to scale software packages to unique needs now and over time. Multiple math engines can easily and accurately formulate opaque, translucent and transparent colours at fixed loads or with minimised pigment usage. With all databases operating from the same structure in a network installation, managing colour standards and measurements makes X-RiteColor Master the most efficient software for enterprise and supply chain processes.


    Colorimeters are not spectrophotometers. Colorimeters are tristimulus (three-filtered) devices that make use of red, green, and blue filters that emulate the response of the human eye to light and colour. In some quality control applications, these tools represent the lowest cost answer. Colorimeters cannot compensate for metamerism (a shift in the appearance of a sample due to the light used to illuminate the surface). As colorimeters use a single type of light (such as incandescent or pulsed xenon) and because they do not record the spectral reflectance of the media, they cannot predict this shift. Spectrophotometers can compensate for this shift, making spectrophotometers a superior choice for accurate, repeatable colour measurement.

    Special effect and pearlescent paint

    The X-Rite MA68II spectrophotometer offers a full range of angular viewing (15° to 110°) for accurate evaluation of the changes exhibited in metallic, pearlescent and special effect paint finishes. The unique dynamic rotational sampling (DRS) technology utilises a simple, robust optical system which provides simultaneous measurement of all angles.The MA68II interfaces with X-RiteColor Master software for complete colour quality control applications.

    Sphere and 0/45 Instruments

    X-Rite offers a wide range of sphere and 0/45 spectrophotometers in portable and countertop models that offer superb inter-instrument agreement and repeatability. These instruments are easy to use and can be set up for streamlined, automated capture of colour data.

    Non-contact colour measurement

    The X-Rite TeleFlash system provides online colour measurement and evaluation of colour deviation to the running production line. TeleFlash can accurately measure the colour of products that are textured, finely patterned or glossy, such as extruded vinyl, bulk goods, coil coatings, synthetic films, paints (wet and dry), coated leather, carpeting, granules, food pigments, paper, powders, glass, ceramics, metal, minerals and plaster. TeleFlash offers a measuring distance of up to five feet, tolerating small variations in the measuring distance from system to sample. The system's thermochromism compensation allows for colour measurement without the time usually required for cooling and stabilising.

    Multi-user, network installations and portable data

    The networkability of X-Rite software makes it easy to communicate data and share standards across an enterprise. This ease translates into efficiency which has a direct effect on profitability. For applications without networked computers, X-Rite Colour-Mail can be used for fast, easy communication of colour data via standard e-mail. ColorMail can be a seamless part of X-RiteColor Master software.

    Calibrated, on-screen colour

    X-Rite offers the only colour formulation and quality assurance software to use the International Colour Consortium's (ICC) standard device profiles for on-screen colour. This means that colours will be consistently displayed on different computers, so long as ICC profiles are used. Use X-Rite monitor optimizers and auto-scan densitometers for complete colour calibration and control on computers, printers and scanners.


    Spectrophotometry's applications are seemingly boundless. A typical user will make colour measurements many times a day, comparing production to clearly defined standards. Spectrophotometry assisted colour measurement can be useful in areas such as:

    * Corporate logo standardisation

    * Colour testing of dyes and inks

    * Colour control of coated leather

    * Control of printed colours on packaging material and labels

    * Colour control of plastics and textiles throughout the development and manufacturing process

    * Finished products like printed cans, clothing, shoes, automobile components, plastic components of all types

    To obtain free copies of 'Understanding Colour Communications' please contact X-Rite on +44 1625 871100 or email nmasales@xrite.com with your name and address details. To find out more about colour communications or to attend one of X-rite's training days, telephone the above number.

    Created by:LANCEY, Ms. Raphaelle 25/03/2008 4:58:17 PM
    Modified by:LANCEY, Ms. Raphaelle 25/03/2008 4:58:17 PM

    TA.1.12. - Vegetable Tanning

    The profile of vegetable tannins: properties and performance - October 2005
    Contributed by: Leather International magazine
    Last updated: 22/09/2008 5:12:17 PM

    The purpose of vegetable tanning material is similar to the other types of tanning materials commonly used in the leather industry, namely to bring about irreversible stabilisation of the skins/hides. By Farrukh Nazir, senior scientific officer, PCSIR Leather Research Centre, Karachi, Pakistan.

    Tanning materials can be classified into three main groups according to their chemical nature:

    1 Aromatic tanning material (eg synthetic and vegetable tanning agents)
    2 Mineral tanning material (eg chrome tanning agent)
    3 Aliphatic tanning material (eg aldehyde tanning agent)

    The vegetable tannins are widely distributed in the plant kingdom and occur in different concentrations in all parts of the plant materials, whether bark, fruit, wood, or roots. But those parts of plants which contain a large amount of tannin are technically feasible.

    Some of the popular veg tans can be seen in Table 1.

    Chemistry of vegetable tannins

    The chemistry of vegetable tannins is little known. Therefore, a firm definition of what constitutes vegetable tannin is not easy to find. Probably the most acceptable definition is still that of Bate-Smith and Swain, formulated in 1962. They adopted the earlier ideas of White and described vegetable tannins as water soluble polyphenolic compounds having molecular weights between 500 to 3,000 and, besides giving the usual phenolic reactions, they have special properties such as the ability to precipitate alkaloids and proteins (Haslam, 1988).

    The non-tans are other water-soluble phenolic/non-phenolic compounds, which may disperse the large aggregated molecules of 'true tans'. The non-tans consist of sugary matter, salts, flavones, gallic acid and other acids.

    Vegetable tannins are generally classified into two groups:

    (1) Pyrogallol tannins or hydrolysable tans and (2) Catechol tannins or condensable tans. Their basic structures are shown in Figure 1.

    Hydrolysable type

    The hydrolysable tans have been further subdivided into two groups:

    (A) Gallotannins

    On hydrolysis these yield gallic acid and glucose, eg galls (pathological growths, called galls, present on the leaves of certain species)

    a) Turkish galls are found on oak species
    b) Chinese galls are found on sumac species

    (B) Ellagitannins

    On hydrolysis these give ellagic acid and glucose, eg myrobalans and chestnut wood.
    This type of tannin has the characteristic property of undergoing hydrolysis to form 'sludge/bloom'.

    Hydrolysable type

    The condensable tans are not prone to hydrolysis but they are liable to oxidation and polymerisation to form insoluble products known as 'Tannin reds/phlobaphenes'.

    The commercially most important tanning materials like avaram, babul, hemlock, mangrove, mimosa, quebracho etc, belong to this group. The major differences between the two types of tannins are displayed in Table 2.


    Mechanism of tanning

    In mechanism of vegetable tanning, acidic groups of vegetable tannins may combine with the basic groups of the hide collagen by polyfunctional cross-linking via so-called hydrogen bridges. The mechanism of vegetable tannins is indicated in Figure 2.

    The factors responsible for influencing the tanning mechanism during leather processing are as follows:

    Condition of pelt

    The condition of a pelt is said to be the most ideal if the collagen fibres are clearly separated. This inter-fibre separation is dependent on liming, deliming and any pretanning processes.

    Particle size

    Tanning solutions are colloidal in nature and they contain tannin particles of different molecular weights.

    The low molecular weight compounds are too small for effective cross-linking and high molecular weight compounds are either insoluble or too large for cross-linking with polypeptide chains.

    So tannin solutions in the range of 500-3,000 molecular weights can suitably associate with protein molecules to form stable cross-linked structures.


    Tanning takes place over a wide range of pH, but fixation varies considerably at different pH levels. If the pH is lowered sufficiently, fixation is so rapid on the outer layers of the pelt that further penetration virtually ceases. This state is called 'case hardening'. It should be noted that at the iso-electric point of collagen, tan fixation is at its lowest. For this reason, tanning is recommended at about pH 5 where tannin fixation is at its minimum and penetration at its maximum. After full penetration is achieved, the pH of the whole system is lowered, usually with an organic acid which has the effect of 'fixing' the tan in the interior of the leather.

    Low pH - High Fixation

    Acid and salt content

    The major non-tannin constitutes of a tanning liquor are natural acids and salts. The amount of acid and salt varies in different tanning liquors and these substances greatly influence the character of leather. If the salt content is too high the resultant leather will be soft while high acid contents gives firm leather.
    Generally speaking the catechol tanning materials contain low acid content whereas the pyrogallol tanning materials have comparatively high acid content.

    The most astringent tanning materials, eg quebracho and mimosa contain low acid and salt contents.

    Relation of tannin to acid and salt contents

    Low acid content - High diffusion or penetration

    Low salt content - High fixation or combination


    The rate of diffusion is closely bound up with temperature. If the temperature is allowed to fall to freezing point, tannage virtually ceases. Increase in temperature up to a certain limit will accelerate diffusion of the tan liquor into the pelt.

    Good diffusion is a necessary condition for achieving correct tanning fixation.

    Tannin concentration

    The amount of tannin penetration and combination with the hide substance is governed largely by the actual concentration of tan liquor in contact with the fibre. In the early stages of the tanning process, tannin concentration in the outside liquor is stronger than that of the internal liquor between the fibres, the faster diffusion will occur.

    If the tan concentration in the outside phase is doubled, fixation is increased sufficiently. Thus, diffusion and fixation depend to a large extent on each other. A 20-35 % tannin concentration of 80-140 barkometer is found beneficial for rapid tanning.

    Importance of vegetable tannins

    Most types of leather, from compact, firm sole leather to soft lining leather, can be manufactured by vegetable tannage. Of all the vegetable tannins produced in the world 90% are consumed by the leather industry. Of this, 65-70% is used by the heavy leather industry and the rest by the light leather industry. Vegetable tannage of light and heavy leather require 18-20% and 25-30% tannins respectively.

    In addition, the recent increase in the awareness of the use of ecofriendly materials in processing industries has seen a growing demand for vegetable tanning materials as they are one of the few environmentally friendly products causing minimum pollution/effluent problems. The effluents thus generated in the process are biodegradable.

    Created by:LANCEY, Ms. Raphaelle 19/09/2008 11:10:33 AM
    Modified by:LANCEY, Ms. Raphaelle 22/09/2008 5:12:17 PM

    TA.1.13 - Automotive Upholstery

    New fatliquors for car upholstery leather - November 2005
    Contributed by: Leather International magazine
    Last updated: 19/09/2008 11:21:36 AM

    According to Zschimmer & Schwarz, two important requirements for automotive upholstery leather are ageing resistance and the nature of evaporation or sublimation of chemical substances.

    When it comes to physical requirements, car upholstery leather differs from normal upholstery leather. Out of many, Zschimmer & Schwarz say that two requirements stand out as being particularly important:

    1. Evaporation of chemical substances
    2. Ageing resistance

    The evaporation of substances is determined by carrying out fogging tests, eg according to DIN 75201 or SAE J 1756 and static or dynamic headspace according to VDA 277 and 278. All evaporating or sublimating substances in the leather can be detected with these methods under defined conditions, such as temperature and time.

    The ageing of the leather is influenced by heat and light-resistance but also by the resistance to environmental cycles (climatic chamber test).

    An important point in order to meet the physical expectations, is the correct choice of fatliquor. Latest results of analysis, made by headspace chromatography, show the responsibility of substances for emissions, especially compounds with a high vapour tension. These can be hydrocarbons and oils, as well as waxes with a relative low boiling point and substances without any linkage to the fibres are risky. Also substances with the tendency to sublimate, such as nitrogen products or ammonia-salts, have to be avoided.

    For the ageing of leather, the parts of unsaturated substances in the fatliquor are responsible. In this case, for example, fish oil or vegetable-oils contain unsaturated fatty acids. The high offer of double-bonds makes an oxidation possible. It can result in a yellowing-effect, unpleasant smell and a hardening of the leather.

    Out of this experience and knowledge, Zschimmer & Schwarz have developed a range of products for car seat leather.

    Prinol CRC is particularly suitable for pre-fatliquoring. The product is based on a synthetic ester sulfonate and shows an excellent stability to all electrolytes. It can be applied in a pH below 2 (eg pickle for unsplit hides). It is easily soluble in cold water and can be added directly to the float. Prinol CRC is able to reduce the emission of volatile substances (fogging, haze, VOC, FOG). Furthermore, Prinol CRC has the following advantages:

    * an accelerated even absorption of all chemicals in the pickle and tannage
    * a very good exhaustion coupled with a low extractability
    * good softness and grain elasticity
    * excellent light and heat fastness

    Prinol CRC treated wet-blue or wet-white material generally shows an improvement in mechanical processes such as sammying and shaving.

    Prinol F-GB is a main fatliquor for all types of car seat leather. The product is based on a combination of polymeric, synthetic and natural softeners not containing any fish oil. It is easily soluble in cold water and can be added directly to the float. The application of Prinol F-GB results in an excellent softness and a pleasant touch. All fogging values such as VOC and FOG are very low. The heat and light fastness, as well as a neutral odour, is also very good.

    Provol CAD is a main fatliquor for chrome-free automotive leathers, resulting in a very good softness, body and touch. The product is based on a combination of natural and synthetic oils with special emulsifiers, containing a high amount of high-grade lecithin. It does not contain any fish oil. All emission values such as fogging, VOC and FOG, are very low. In the following figures the influence of the products to the emission of volatile substances is described graphically.

    Created by:LANCEY, Ms. Raphaelle 19/09/2008 11:21:36 AM
    Modified by:LANCEY, Ms. Raphaelle 19/09/2008 11:21:36 AM

    Fogging for automotive leathers - the new EN 14288/ISO 17071 test method - November 2005
    Contributed by: Leather International magazine
    Last updated: 22/09/2008 5:12:58 PM

    One of the most important tests which automotive upholstery leather has to undergo determines its potential for fogging. Campbell Page, Jolanda Noger and Sabine Dickhaut-Güdemann, TFL Ledertechnik AG, Basel, Switzerland, co-wrote the following paper which Campbell Page presented at the IULTCS Congress in Florence earlier this year.


    One of the key emission tests that leather is required to undergo by the automotive industry is its propensity to fogging, that is, the ability when heated to emit substances that form a haze-like layer on the windscreen of a car. Naturally the automotive industry requires that the interior materials of a car do not exhibit this fogging effect to any significant effect.

    Until now the German DIN 75201 test method adopted in 1992 has been the standard reference for many supplying leather to the European automotive industry. Variations on this method have been used by other non-European automotive manufacturers.

    In December 2003 the European Committee for Standardization, CEN, released a new European Standard test method for the determination of fogging characteristics for leather. This Standard test method is EN 14288 Leather - Physical and mechanical tests - Determination of fogging characteristics. This test method is also in the process of being adopted as an ISO Standard, namely ISO 17071.

    With the new EN method, the limits of the reflectometric procedure are clearly indicated and there are some practical changes in the test parameters when compared with the DIN procedure. The new EN method more closely reflects that which is being used in many tannery test laboratories.

    A study has been undertaken to evaluate the influence of the new parameters on the test results for automotive leathers. A further study has been made to compare several of the differing test methods used internationally.

    The results and their implications for automotive leather suppliers are presented.

    It has been well documented over the past years which leather processes and which chemicals influence the degree of fogging that occurs, so this aspect does not form part of this presentation.

    New, highly sophisticated methods for measuring and analysing the emissions from automotive interior trim materials are starting to be requested by some car manufacturers (1). Typically these tests are made using gas chromatographic head space techniques and typically involve extremely small samples (eg 10mg) and temperatures in the range 90-120°C. No doubt these new procedures will develop further but the basic standard for the tannery remains the traditional fogging test method.


    With a large amount of work, the German Standard, DIN 75201, was published in 1992 as the definitive method for measuring fogging of automotive interior trim materials. The DIN 75201 method is actually two completely separate test procedures, which were unfortunately mixed together in the one Standard.
    Method A is the so-called reflectometric method that measured the opaqueness of the fogging layer on a cold glass surface.

    Method B, the gravimetric method, measured the quantity of condensate that formed on a cold surface.

    The results obtained from Method A and Method B have been found to have no relationship with one another as they are measuring different parameters.

    Why was there a need for a new method?

    Over the past ten years, it was quite noticeable that different test houses were obtaining considerably different results for one of the two methods, namely the reflectometric method.

    Additionally for very practical reasons, many suppliers of automotive leather were not following precisely the DIN 75201 procedures and had introduced their own variations to the methods. In the present day, to hold a production lot for up to ten days to await a quality test result is economically impossible.

    The DIN Standard incorporated two quite different test procedures but they were not separated in the text. So it was difficult to clearly follow one or the other method on its own. Over time, it was obvious some additional explanations to the methods were necessary.

    It was necessary to evaluate the significance of these aspects and if they could be incorporated into a new Standard.

    What is the fogging test as in EN 14288 and DIN 75201?

    The standard procedure for testing the propensity to cause fogging involves cutting an 80mm diameter circular sample of leather and removing absorbed water by drying over a desiccant. This sample is then placed at the bottom of a tall glass beaker, which is immersed in an oil bath heated at 100°C. The top cover of the beaker is cooled at 21°C to allow the substances emitted from the leather sample to condense on the cool surface.

    In the case of the reflectometric method, a glass plate (at 21°C) covers the heated beaker for 3 hours. The glass plate is removed and, after conditioning, the opaqueness of the condensate is measured with a reflectometer.

    For the gravimetric method, the top of the heated beaker is covered with a pre-weighed aluminium foil (at 21°C) for 16 hours. The aluminium foil is removed and dried over a desiccant for four hours before re-weighing.

    Are there other procedures than the DIN method?

    Yes. As is common in the automotive industry, different car manufacturers have introduced their own variations of this procedure. Some specify heating the sample less, for example only to 85°C or 90°C, and cooling the glass plate less, for example to 38°C.

    These parameters give quite different results when compared with the DIN procedure. Hence it is extremely important that the test method parameters are presented along with the results obtained.


    1) Why is the reflectometric method less used?

    It has been very noticeable that the inter-laboratory variations in results for Process A, the reflectometric method, have resulted in many of the European automotive manufacturers now specifying only the much more consistent Process B, gravimetric method.

    A well reported inter-laboratory trial (2) using results from seven laboratories confirmed this variation. The results are shown in Table 1.

    Various additional round-trials were undertaken to try and identify the reason for the variability in Process A. Variations in drying agents, temperature of the oil bath and cleanliness of the glass plates did not result in an improvement in the inter-laboratory agreement.

    For the reflectometric method, the automotive manufacturers typically set specifications in the range of 60-90%. As shown above, the inter-laboratory confidence interval for this range is quite large, approximately 25, such that a definite compliance with the specifications is almost impossible to ascertain. Even if the repeat testing within the one laboratory shows very good agreement, it is the testing between laboratories that is the critical variance where problems occur.

    For the gravimetric method the requirements from the automotive manufacturers vary from less than 3mg to less than 7mg. In this range, one can conclude that a typical inter-laboratory confidence for the test results is around 1mg .

    Furthermore, the new EN 14288 test method now clearly separates the two procedures into Method A and Method B. The new Standard informs the user that there is no mathematical correlation between the results from the two methods. Moreover, it clearly explains that the reflectometric Method A has high variability in results.

    2) Using alternative drying agents

    In DIN 75201, the leather samples are required to be dried using the drying agent phosphorous pentoxide, P2O5. This chemical has handling problems especially for staff not well trained in the use of chemicals. P2O5 combines with moisture to form a very corrosive acid. Further, once the surface of the chemical is wet from absorbed moisture, this layer blocks the underlying P2O5 from absorbing further moisture. Reusable silica gel is commonly used as a laboratory drying agent and many tanneries have adopted it for the fogging test.

    Comparison of the gravimetric values of leather samples dried over two different drying agents confirmed for tannery test laboratories that while the phosphorous pentoxide gave the lowest results, for production QC purposes, in many cases a two day drying over reusable silica gel was capable of giving results within the specification. Results for two leather samples are shown in Table 2. They are representative of results from many leather samples.

    The new EN 14288 test method still recommends phosphorous pentoxide as the drying agent but importantly it allows for the use of alternative drying agents when they give equivalent results. This reflects the situation which is being practised by much of the industry, both in the tanneries and by automotive companies.

    3) Are long drying times necessary?

    The long drying time requested prior to testing for items made of natural products, such as leather, has been a big problem for tanners. A seven day drying time before even starting to carry out the test is, in most cases, not economically possible today.

    A series of different leather samples were dried over two different desiccants; phosphorous pentoxide and reusable silica gel. The weight loss after two days and seven days was measured:

    Leather weight loss (%)
    Weight loss after 2 days
    Phosphorous pentoxide 2.8%
    Reusable silica gel 4.6%
    Weight loss after 7 days
    Phosphorous pentoxide 5.3%
    Reusable silica gel 6.5%

    So taking into account the ease of handling and reusability, the results clearly support the use of reusable silica gel as the desiccant of preference for use in tannery test laboratories. This drying agent removes moisture quickly allowing a prompt testing of the leather.

    The new EN 14288 test method recognises the economical constraints of production and allows the use of two days for the drying of samples. A repeat using the traditional seven days is offered in cases when a sample fails to meet the customer's specifications.

    4) Interpretation of the fogging condensate

    Reflectometric Method A is only valid for those condensates that form fine 'fog-like' particles spread relatively evenly over the glass surface. Often larger transparent droplets and films can form; in this case the method reports them as having little reflection, implying a good result, when the truth is that the results are very bad. A visual evaluation of the condensate is important. It is clear from numerous 'unusual' test results seen that in many cases this aspect is overlooked and the glass plate reflection value is simply measured regardless of the condensate type.

    The new EN 14288 test method requires a visual assessment of the condensate and if it is a transparent film or similar, then the test procedure is stopped at this point, as the reflectometric method is not able to give meaningful results.

    5) What influence do different test parameters have on the result?

    The SAE J1756 test method for fogging has various options for heating the sample and the temperature of the cooling surface.

    An evaluation of the differences between the EN 14288 / DIN 75201 Method A conditions was undertaken. This involved three hours heating at 100°C and 21°C condensate cooling and the commonly used SAE J1756 test method option with six hours heating at 85°C and 38°C condensate cooling. The reflectometric results taken after one hour conditioning are shown in Table 3.

    For this SAE J1756 method, the lower heating temperature of the leather sample and the higher temperature of the cooling glass plate combine to give considerably higher reflectometric values. Additionally, the SAE method is clearly not sensitive in differentiating between leather samples when compared with the EN 14288 / DIN 75201 procedure. In fact the reflectometric results using this option of the SAE method do not vary even if the leather test sample is not dried prior to testing!

    Therefore, it is clear that the test parameters are very important and, as indicated here, it is extremely difficult to compare results for different car manufacturers as most have different test parameters.


    While the new EN 14288 Standard retains the basic elements of the traditional DIN 75201 Standard, it has been introduced to update the procedures and align with the practices being used by the industry. It takes into account tanners' economic needs and gives results which can be confidently used to meet customers' needs. The EN 14288 Standard is also in the process of being introduced as an ISO Standard, namely ISO 17071.

    Created by:LANCEY, Ms. Raphaelle 22/09/2008 2:42:44 PM
    Modified by:LANCEY, Ms. Raphaelle 22/09/2008 5:12:58 PM

    TA.1.14. - Formaldehyde

    Formaldehyde in leathergoods: remedies and solutions - December 2005
    Contributed by: Leather International magazine
    Last updated: 22/09/2008 5:05:52 PM

    Growing concern about health and environmental problems has led to a whole new generation of environment-friendly processing systems. Eligio Stoppa, FGL International SpA, presented the following paper at the ACLE in Shanghai in September.

    Evolution of the market, application and cognitive technologies have in recent years significantly modified the requirements that must be met in the production of consumer goods.

    The constantly growing interest in 'health' at a worldwide level and, therefore, with regard to environmental problems, has led the industrial system to an increased attention to 'environment-friendly quality' articles.
    For this reason, Ecolabel trademarks and design labels have been established, such as:

    * Oeko - Tex standard
    * SG trademark
    * ICT ECO - tox guidelines No.1/96
    * Draft EU Ecolabel for footwear

    and copious technical drafts for specific sectors including car upholstery or footwear and involving numerous, more or less restrictive control parameters.

    Of all the parameters, special attention must be paid to the aspect of free formaldehyde, its presence in leathergoods being considered strictly linked with the kind of chemical products used in the manufacturing process.

    In articles, free formaldehyde is permitted only within very strict limits of 150/50 ppm max for the purposes of certain trademarks (SG) and usage; in some cases even lower limits are applied, eg in the car and footwear industries. In order to handle this important subject, it is crucial to know and systematically assess all aspects, to enable us to prepare all the corrective and preventive measures to produce articles that meet the necessary requirements.

    Formaldehyde in leather

    Formaldehyde, the simplest of aliphatic aldehydes, is of considerable importance in the wider chemical industry, in synthesis, and has known industrial scale production for more than a century. It is used in the production of foam plastics, plastic products for engineering, regenerated wood, paints, dyes, vitamins and in preparations used in the paper industry.

    In the tanning industry, it is used as a tanning agent, as a casein fixing agent in finishing and is used in the production of pre-tanning, tanning and re-tanning agents based on synthesis and condensation, such as tannins and resins.

    Products most commonly used in tanning, involving synthesis based on polymerisation and condensation of various substances, including formaldehyde, are as follows:

    * Synthetic tannins
    * Melamine and dicyandiamide resins
    * Urea - formaldehyde etc

    As is known, synthetic tannins contain more phenolic functions, obtained by synthesis and used as principal or auxiliary agents (to aid solubilisation and penetration of vegetable tannins and dyes) in tanning. They were studied and synthesised mainly to produce substitutes for natural tannins, commencing from a base molecule such as phenol which, after preliminary sulphonation treatments, underwent condensation with a loss of one water molecule.

    Figures 1 and 2 show two reaction diagrams.

    In the case of the tanning industry, synthetic resins are achieved by polymerisation and/or condensation from a monomer, then the required reactions (suitably varying temperature and pH) are performed in situ (in the leather) in order to obtain polymers, possibly straight chain.

    From the various diagrams, it is clear that formaldehyde used as a condensing agent will certainly be present as a non-reacted element in products and will also be encountered, not only in tannins or resins, but also in all other products synthesised by this process.

    However, it must be emphasised that the use of products in which formaldehyde is present as a residue of reactions, will offer a modest contribution with respect to its direct use. In fact, the quantity of formaldehyde may be optimised, ie so that its presence is the minimum possible, if at factory level the production process respects the stoichiometric ratio and takes account of certain important parameters such as: temperature, rotation times, agitation speeds etc.

    As a matter of fact, the situation is completely different when using compounds such as vegetable tannins, polymer tanning agents and glutaraldehyde, which offer no contribution to the formaldehyde in the leather. Naphthalenic and sulphonic tanning agents are also comparable with vegetable tanning agents provided that the above parameters are respected.

    In tanning and re-tanning, formaldehyde can react with collagen-free base groups to form methylene compounds via an alcohol condensation reaction (a stable C-C methylene bond is formed which remains intact under analysis conditions) as shown in Figure 5. 


    In this kind of tanning, the bond is covalent and, in particular, the pH interval of 6-8 used in practice is ideal for achieving the set maximum quantity. When tanning application conditions are such that they guarantee this kind of bond, the problem of free formaldehyde would seem to be inexistent, in the sense that drastic hydrolysis conditions would be needed to free it. It is no coincidence that the main analytical method to determine the bonded formaldehyde involves hydrolysis of the leather using sulfuric acid and subsequent distillations.

    The use of formaldehyde as such, and of products that release it by decomposition, will become increasingly less diffused as formaldehyde limits are lowered, with the aim of achieving environment-friendly articles.

    Formaldehyde: characteristics and assessment analysis methods

    Formaldehyde is not easy to handle: it has a penetrating odour, irritates the eyes and mucous membranes, and skin exposure to formaldehyde in those subject to allergies may induce allergic reactions. According to current regulations on the subject of labelling and hazardous preparations, formaldehyde in a maximum 50% solution is classified with the toxic T symbol, with the following hazard warnings:

    R 23/24/25 Toxic by inhalation, in contact with skin and if swallowed
    R 34 Causes burns
    R 40 Possible carcinogenic effects
    R 43 May cause sensitisation by skin contact

    Besides its allergenic properties, formaldehyde was indicated as a potential carcinogenic agent during experiments conducted in 1980 by the Chemical Industry Institute of Toxicology in North Carolina (USA).
    Nevertheless, formaldehyde was classified by the European Union as a suspected carcinogen under Category 3, and this has certainly accelerated efforts to lower limits in leather and articles in general.

    Formaldehyde may be present in articles in free form, reversibly or irreversibly bonded. Among the numerous methods developed to identify it, the more significant are those operating in the gaseous phase (AUDI/VW) PV 3925 and in aqueous media DIN 53315.

    Free formaldehyde, which is not bonded to the leather itself or to other substances applied to the leather, may be measured by the gaseous phase method. Reversibly bonded formaldehyde is measured by the water extraction method (results obtained via the extraction method represent the total of reversibly bonded and free formaldehyde); irreversibly bonded formaldehyde, ie the total formaldehyde content, may be assessed for example by treating the leather with sulfuric acid and subsequent distillation.

    Water extraction and gaseous phase analysis methods are compared in Table 2.

    Skins containing formaldehyde within required limits: how are they produced?

    The tanning industry needs to aim for clean products and processes. Therefore, innovative solutions are required to achieve this objective. Clearly, the greater undertaking falls to those producing and marketing chemical products for manufacturing processes but the technical and applicational contribution to the product is equally fundamental, with a mental approach that aims to optimise the application by exploiting all acquired know-how.

    To achieve the objective, steps are necessary on various fronts:

    * to produce products such as tannins, high-quality resin products, by developing advanced chemistry and technical systems that reduce formaldehyde content to a minimum

    * to produce skins by methods that take into account the characteristics of applied products

    * to introduce the use of new concept substitute products that overcome the problem and achieve the same product results

    * to study new products and application techniques, for cases in which the use of condensation products requiring formaldehyde is inevitable, in order to reduce its quantity

    In this respect, FGL International, aware of this need and with the intention of remaining close to customers by meeting user requirements, have produced a range of low formaldehyde content products which, on application, respect the limits set by law and/or technical drafts.

    * Research and production optimisation has led to the Lecosin range of synthetic tannins and Lecoren melamine and dicyandiamide resins with a reduced free formaldehyde content which, if used in appropriate quantities and type, allows the production of articles that respect legal requirements.

    * Re-tanning agents have also been researched as an alternative to classic phenol, melamine and dicyandiamide condensation products, by producing synthetic polymers with strong crosslinking power and re-tanning ability in the Permasol and Idrosin range.

    * The research and constant efforts underlying FGL International business activities has also produced Permasol TFR, a product able to intervene when the use of products containing formaldehyde that increase values beyond set limits is inevitable.

    Permasol: characteristics and applicational advantages:

    Reacts irreversibly with free formaldehyde and forms stable bonds, reduces the formaldehyde level to bring values well below set limits. The use of Permasol TFR is a valuable aid when the use of classic condensation products containing formaldehyde is inevitable in order to respect the technical requirements of particular articles.

    By application in various kinds of skin recipes involving the use of phenolic, dihydroxyphenyl sulfone and melamine resin synthetic tannins and repeating the same process on the other half of the skin using Permasol TFR, free formaldehyde values proved to be halved.

    The resulting average values are given in Table 3.


    The continuous development of market and legal requirements force industry, including the tanning industry and related sectors, into facing constant challenges and adaptation.

    With the awareness that all of this is necessary to improve workplace and environmental quality, the aim for all parties involved must be that of undertaking the research and development of production and application techniques to achieve products that meet requirements.

    Created by:LANCEY, Ms. Raphaelle 22/09/2008 3:47:43 PM
    Modified by:LANCEY, Ms. Raphaelle 22/09/2008 5:05:52 PM

    TA.1.15. - Salinity

    Salinity reduction in tannery effluent - January/February 2006
    Contributed by: Leather International magazine
    Last updated: 22/09/2008 5:14:32 PM

    Salinity in tannery effluents, measured as TDS (Total Dissolved Solids), is a critical problem in many countries, particularly India and Australia. Catherine A Money, CSIRO Leather Research Centre, Australia, and N K Chandra Babu, Central Leather Research Institute, India, were both involved in the following project.


    About 60% of Indian tanning occurs in Tamil Nadu where there is a discharge limit for TDS of 2,100mg/l. The Pollution Control Board insists that some tanneries install Reverse Osmosis but this does not solve the salt problem. The aim of a joint CLRI-CSIRO-ACIAR project is to develop and apply industrially viable systems to eliminate or significantly reduce salt use in hide and skin preservation and processing.

    The four major components of the project are:

    * reduced salt in curing

    * short-term preservation with chemicals or chilling

    * pickle liquor recycling
    - in vegetable tanning (India)
    - woolskin processing (Australia)

    * direct chrome liquor recycling (DCLR)

    In Australia, some tanneries have significantly lowered the total amount of salt discharged, mainly by processing green rather than salted hides and by directly recycling chrome tanning liquors (DCLR) (1,2). At the same time, water use has been greatly reduced. Short-term preservation with chilling or chemicals is used to facilitate green processing. Because sodium chloride levels are low, these tanneries are able to use the effluent for irrigation purposes even though the TDS can be over 10,000mg/l (3,4). Many components of the TDS are beneficial but the application rate must be monitored.

    In India, goat skins are salted with 50-100% salt by weight and hides with 40-50%. In Tamil Nadu, soak liquors from the soaking of salted skins are required to be evaporated in solar pans but this is usually inefficient and little salt is removed from the site. Used salt removed from skins before processing is also an environmental problem. Unido has already implemented systems to reduce the amount of salt discharged in tannery effluents (5). Low salt systems with additives have been investigated in the current project with encouraging results and chilling of hides and skins is also being tried in India.

    Australian woolskins are available only seasonally and they are salted then tanned throughout the year. Low salt systems with additives have been investigated for woolskins which do not require prolonged storage. Tannery process improvements which have the greatest impact on TDS reduction are pickle recycle and DCLR.

    Low salt preservation

    Drying and dry-salting of goat skins has been investigated but it is unlikely that they will be adopted for skin preservation in India. Many short-term preservation systems have also been investigated but are not suitable for the rigorous Indian conditions. Low salt systems with additives have given promising results and are being trialled commercially. They could reduce salt use 3-4 fold which will be a significant reduction. Now that skins are not bought by weight, the weight of salt used does not affect the skin price.

    It is feasible for the first handlers of Indian goat skins to salt unopened skins by rubbing salt on the flesh side as usual but with about 20% salt by weight rather than 80% salt. It will be most important that wet skins are drained well before salting. The skins will then be turned hair out.

    The scrotum will remain on the skins and must be well salted. Collection centres, often already controlled or influenced by tanners, could apply additives as necessary to preserve the skins for 7-28 days as required. It is also possible that the additive is mixed with the salt prior to application.

    This low salt system could reduce salt use 3-4 fold and there will be little excess salt on the skins and little solid salt waste. Evaporation of soak liquors will be required, as is the case at present. As waste salt will be significantly reduced, all the evaporated salt should be able to be re-used or used as a fertiliser for coconut palms.

    The choice of additives is critical and health, toxicity and environmental effects must be considered. It appears to be advisable not to use boron or zinc compounds or sodium fluoride for preservation in India. It is unlikely that the Indian Environmental Charter, which excludes the use of boron compounds, will be changed. The concentration of zinc and boron in Indian tanning centres could lead to a build-up of damaging levels in soils.

    A large range of chemicals has been investigated as salt additives for low salt preservation of skins. Trials show that provided there is 20% salt on skin weight, insect infestation is controlled.

    Laboratory trials have indicated the most suitable additive to be magnesium oxide. Sodium carbonate could also be used but for hand application, magnesium oxide is preferable.

    The alkaline treatments have not caused any unhairing problems due to immunisation. Good preservation for one month is also achieved with 20% salt plus 0.5% naphthalene but health and environmental issues must be considered.

    Industry trials using 20% salt and 2% magnesium oxide on skin weight have produced high quality leathers after storage for a month. Even transport from Delhi and storage in Tamil Nadu during hot summer conditions did not cause grain damage.

    It was found to be advantageous to extend the soaking time to 18 hours and use a soaking enzyme to ensure that the leather quality is comparable with leathers from conventionally salted skins.

    Australian companies are collaborating in commercial trials of flat salting woolskins with low salt levels and have compared several additives and produced good quality finished woolskins.

    The salt application equipment has been modified to enable the low salt application. It has been found that low salt preservation using sodium fluoride and boric acid as additives could reduce salt use seven fold. These additives have been used for many years in Australia. The storage time required for the skins will determine the salt reduction achieved.


    Elimination of salt for hide and skin preservation would have the greatest impact on reducing TDS. Chilling in chillers or with ice has been widely used in Australia for many years (1). Chilled hides are usually kept for only a few days but some are kept for over a week at low temperatures.

    Chilling was thought to be too difficult for Indian conditions but it now appears it may be viable for some hides and skins. If hides and skins are available in large numbers in a region within a relatively short drive from a tanning centre, chilling could be feasible.

    Chilling is increasingly being used for food storage and transport in India and CLRI has completed hide trials and costings which are very encouraging. Chillers rather than ice are considered to be best for India.

    A mobile chilling unit designed for industry trials and demonstrations will initially be used for chilling hides in Kerala and transportation to Erode. Ultimately insulated trucks will be used for transport. Some Indian tanners consider that chilling could overcome their salinity problems.


    Pickle liquor recycling

    A collaborating Australian woolskin tanner has recycled commercial pickle liquors for more than 250 cycles. Previously, pickle liquors were discarded after 20 uses. The recycle liquor reached a steady state after cycle 11 with respect to pH, titratable acid and total nitrogen. The pH and total acidity (formic plus sulfuric) at the end of cycles is given in Figure 1. No liquor clarification has been necessary and leather properties are at least as good as standard production.

    A modified DCLR for woolskins has been used successfully for more than 150 cycles. This system does not give greater overall TDS reduction than the two stage pickle and tannage recycle but does reduce labour costs. The tanner is satisfied with the commercial acceptance of skins from both recycling systems. Trials of pickle liquor recycling have also been successful at Indian tanneries producing vegetable tanned goat leathers with no difference in the quality of the leathers.

    Direct chrome liquor recycling

    DCLR has been used for many years in Australia (6) and reduces the use of both sodium chloride and chrome powder, which contains up to 30% sodium sulfate. Spent chrome liquors are used for the subsequent pickle after acidification to pH<1. Excess chrome liquors are precipitated and the chrome re-used as illustrated in Figure 2.

    The greatest savings in salt use are made if the spent chrome liquor from the drum is collected undiluted for recycling and diluted liquors are precipitated. Good practice allows indefinite re-use of the chrome liquor. Total chrome precipitation from all spent chrome liquors results in far higher TDS levels.

    Preparation of pickle liquor

    * The recovered chrome liquor is screened and grease is skimmed if necessary

    * The liquor must be acidified before it is re-used for the next pack of delimed hides. The usual amount of 98% sulfuric acid is all added direct to the pickle tank. The pH is <1 and this prevents chrome staining. At this low pH, the chromium species present are of low molecular weight and rapidly penetrate the hide (7)

    * When the liquor is acidified, calcium sulfate precipitates and emulsified grease is released. Both can be removed periodically but do not cause a problem in the process

    * The acidification should be done early to allow time for the liquor to cool. Cooling systems can be used

    Typical recycle process

    Delime wash

    Drain well

    * 2% salt (it is vital that the SG is sufficient to control swelling to the same degree as in the normal tannery process)

    * 1% sodium formate

    Drum 10 minutes

    * Add 45% acidified recycle pickle while drumming continuously, check pH, SG/Barko, temperature. Drum as for usual pickle, check pH, SG/Barko, adjust if necessary

    * 5.5% chrome powder

    Usual drumming, fungicide addition, basification and checks

    Unload with little washing

    Following laboratory investigations, successful commercial trials have been undertaken in India. It has been found that it is critical that the drum is rotating during the addition of the acidified pickle. Otherwise drawn grain caused by acid burn can occur. Also, the pickle tank should be covered to avoid fumes.


    Technology for TDS reduction has been developed and demonstrated. However, to achieve significant TDS reductions in India, there will need to be considerable uptake of low salt preservation of skins and chilling of hides. The proposed low salt preservation will entail little change for first handlers of skins but greater care will be required to ensure even salt application. There will be resistance to change. One possibility that may bring about change: the tanner could pay more for skins with less salt and good preservation and less for skins with excess salt.

    The costs associated with chilling will be considerable and it is generally accepted that those who gain from the development should bear the cost. It is a possibility that the government may provide loans which industry would repay. Costs and benefits first need to be determined.

    The collaborating tanners will be the champions of the new technologies. Once a technology is proven to them, they will adopt the new systems and others are expected to follow.


    Salinity Reduction in Tannery Effluents in India and Australia is an ACIAR funded project. T Ramasami, N K Chandra Babu, C Muralidharan, J Ragava Rao, P Saravanan, Central Leather Research Institute (CLRI). Catherine Money, Mark Hickey, Ken Montgomery, Cameron Simpson, Chi Huynh, CSIRO Leather Research Centre.

    Created by:LANCEY, Ms. Raphaelle 22/09/2008 4:27:54 PM
    Modified by:LANCEY, Ms. Raphaelle 22/09/2008 5:14:32 PM

    TA. 1.16. - Tanning

    Trends in non-chromium tannages - March 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 10:19:19 AM


    Whilst there has been, and still is, considerable research into new tanning methods, essentially three systems dominate: aldehyde, chrome and vegetable tanning. Each of these tannages produces leathers with different properties but, in general, there seems to be a move towards non-chromium tannages, especially within the automotive sector.

    It is of interest to evaluate the differences between two of the main types of tannages and the properties of the resulting leathers.

    Chrome tanning

    Chromium now forms the basis of virtually all light leather manufacture. It is relatively cheap, has a well-established technology and most auxiliary chemicals used to enhance leather performance have been developed on the basis of a chrome-tanned substrate. The unique characteristic of chrome-tanned leather is a shrinkage temperature greater than 100°C, which allows it to 'withstand the boil' for a period of time (1-3 minutes).

    The key properties of chrome leather are as follows:

    * Lightweight leather with an attractive appearance

    * High tensile strength

    * Good chemical stability (eg stable over a range of pH3-8)

    * Versatile in physical properties (eg softness, stretch)

    * Dyes and finishes in brilliant colours

    * A certain degree of inherent water resistance

    * Good sueding properties

    * Good permeability to water vapour and air

    * Rapid controllable tannage

    * Good setting and other properties for upper material for footwear

    * High hydrothermal and dimensional stability

    The process of tanning occurs when tanning salts, such as chromium, are able to crosslink collagen protein molecules. This crosslinking action makes the hide less susceptible to the effects of heat and putrefaction.

    The key components in the reaction are the chromium III ion, basifying agent or base, and the collagen molecule. The key reactive molecular group on the collagen molecule is the carboxylic acid group (-COOH).

    When chrome powder is added to the acidified pelt, reactions are established between the chromium, the acid, and the pelt. Collagen molecules are crosslinked via the chromium salt, either by one large chromium complex reacting with two collagen carboxyl groups or by two bound chromium complexes reacting together.

    Chrome tannages are cationic and have good affinity for most chemical products added in the post-tanning stages (retanning, dyeing and fatliquoring). This means that they also respond well to any finish or surface treatments that are applied and, consequently, the fastness properties are usually better than other tannage types.

    There are some issues currently with regards to the use of chromium-tanned leathers. One specific area is their use for toys and children's shoes. Currently chromium-tanned leather is not able to meet the testing requirements of EN71-3 which is a legal requirement for toys.

    Aldehyde tanning (wet-white)

    In some cases, it is preferable to avoid the use of chromium in tannage and other options for wet-white production exist.

    One method for producing wet-white is to stabilise the hide sufficiently to withstand splitting and, more specifically, the shaving operation. In this way, only the preferred portion of the hide receives all processing treatments, and the split and shaving by-products may be disposed of to waste or be differently processed into value-added products such as fertiliser or animal feed. Wet-white is also sufficiently stable that it could be sold as a commodity or stored and transported in this state.

    Properties of wet-white include:

    * An adequate shrinkage temperature (~75°C), which allows splitting and shaving (but is poor for lasting)

    * The shaving and trimmings are chrome-free

    * Possesses a high degree of flexibility so the fibre structure can relax after the splitting process and is set out leading to significant area yield

    Advantages also include:

    * No disposal problems of shavings and trimmings, coupled with the possibility to produce a chrome-free leather

    * Considerable savings in chemicals, as the usage of tanning materials is based on sammed/shaved weight and, furthermore, the process is more efficient, leading to less total chemicals being used

    * With vegetable tanning, the shaving is carried out before the tannage, reducing the problem of iron staining

    * The quality of the leather, particularly in regard to grain tightness, can be improved

    Aldehydes react with the amino groups of collagen (the same groups that react with dyes and fatliquors). This means that it is often the case that more of these post-tanning chemicals are required to achieve a given depth of shade and softness. This type of tanning is now quite widely used in the production of automotive upholstery leathers. It should be noted, however, that aldehyde tanning is not suitable as a sole tannage. It needs to be carried out in conjunction with other tanning agents. Also there needs to be consideration of the potential for formaldehyde release that can occur in some cases. Specifically this is an issue for the automotive industry and again for the production of leather that is used for toys.

    New tanning systems

    The BLC, in collaboration with Loughborough University, is working on a DTI funded project 'Development of a High Stability Chromium Free Tannage'. The project is intending to develop a high-performance, thermally-stable epoxy tannage to be used to produce mineral-free leathers, primarily for the automotive sector within the leather industry. One of the forces behind the push towards mineral-free tanning is the automotive industry. In this sector, there is a definite trend towards an increased use of leather for the internal furnishings of motor vehicles. Other leather sectors are also beginning to examine the potential of chrome-free alternatives.

    Currently, many car manufacturers impose a very strict limit for formaldehyde concentration of 10-ppm for automotive leather which is difficult to achieve. Furthermore, glutaraldehyde-based tanning agents can cause problems within biological effluent treatment plants where the aldehyde can act as an effective biocide. This leads to demands for a mineral-free tanning agent, which can crosslink the carboxyl groups rather than the amine side chains of the skin's collagen, to give the thermal and dimensional stability currently offered by chromium.

    Epoxy resin tannage is not new to leather. It is well known that epoxide reacts with nucleophilic substances which have amino, carboxyl and hydroxy groups and it has been suggested that epoxide reacts with such residues on the collagen fibre. In fact, some investigations on the epoxy treatment of proteins can be found in literature which dates back to 1944.

    Epoxy resins are important industrial polymers widely used in many major industrial applications such as coating, adhesive, civil engineering and casting. There are two characters of these polymers, namely high reactivity and high versatility, which make them suitable for various industrial applications.

    It was found in the earliest studies that epoxy tannages required a high reaction temperature, a long reaction time and a large epoxy resin offer for a shrinkage temperature of 80°C to be obtained. Nevertheless, there were still many positive results worthy to note, including:

    * The leather obtained upon tanning with an epoxy resin has good properties of chemical stability, including resistance to acid, alkali, boiling water and organic solvent treatment. The high stability is due to the introduction of covalent crosslinking bonds by the di- or multi-functional epoxides.

    * Most epoxide tannages are carried out under basic conditions of pH8-9 followed by neutralisation

    * Shrinkage temperatures (Ts) of over 80°C have been obtained within 10 hours at 35°C. Epoxy resins with lower molecular weight or higher functionality result in higher hydrothermal stability. A maximum shrinkage temperature of 90ºC has been achieved by using tetra-functional epoxy resins

    Current research has focused on the use of commercially-available epoxy resins. Initial work concentrated on model systems of individual amino acids (lysine and glutamic acid). This illustrated that the reactivity was appropriate for further trials.

    When one epoxy resin was applied to sheepskin, a shrinkage temperature of 89°C was obtained. Various re-tanning agents are currently being investigated to further optimise the Ts and currently 95°C can be achieved. In addition, a considerable improvement in dye uptake and fixation was shown in comparison with vegetable tanned leathers. This was attributed to the epoxy resin providing additional fixation sites for the dye/collagen interactions.

    At present the main limitation to the industrial application of these resins is their poor solubility in water. Further research is currently underway with the project industrial partners to determine solutions to this issue.

    The project has undoubtedly shown epoxy resins to have huge potential as alternative crosslinkers for use in the leather industry. Large-scale trials are underway to enable a full assessment of the physical performance of the leather produced and in addition the environmental fate of the resins will be evaluated.


    The authors would like to acknowledge the input of the Dr R Heath and Dr Y Di of the University of Loughborough to this project along with the assistance of the other industrial partners. This project work has been part funded by the UK Department of Trade and Industry (DTI).

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 10:19:19 AM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 10:19:19 AM

    TA.1.17. - Traceability

    Leather traceability and authentication - June 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 2:36:59 PM

    The 'intelligent' labelling of products (such as RFID - Radio Frequency Identification) is a suitable solution. However, it does not apply to specific needs in the leather sector, particularly in regards to the processing and use of leather as a material.

    The improvement of authentication systems is vital to guarantee traceability along the chain from the sourcing of raw materials at the abattoir to their use when manufacturing a finished product.

    In this article, the authors have set themselves the task of finding solutions in response to the industry's needs related firstly to leather authentication and secondly to finally assembled finished products.

    Technical guidelines: related to the improvement of a leather authentication system. In general, the integration of an additional step in leather processing that does not have a significant effect on the final performance of the material (therefore on the added value) must be carried out in the most hidden way possible. This is particularly the case when using a marker or labelling system for tracing raw materials. The main clauses to follow in the technical guidelines are related to the way leather is used as well as the way it is processed:

    * Leather as a finished product should not be modified. The colour, touch, thickness and handle characteristics should not be altered by the presence of the marker or label

    * When using leather, its appearance should remain constant. Cutting, glueing, sewing and shaping the material should not be affected by the marker or label

    * Applying the tracer should not modify the manufacturing process. The process involves physical and chemical operations which would be difficult to alter afterwards. However, the application should not need specific equipment, but that already existing within the company

    * The company signature or brand should not be visible to the naked eye; identification should be made possible within the factory with simple means (such as the control of batches throughout the process at the tannery or at the point of receipt by the end-user)

    * The signature or brand must be resistant to physical and chemical conditions during leather making operations carried out prior to tracing

    * The signature or brand should also be resistant to physical-chemical conditions during the manufacturing operations of the finished products manufacturer

    * Finally, cost accountability should be directly related to the technique of adding the marker or label. The extra cost of the marking treatment must be realistic. Especially to materials of strong added value such as luxury or technical leathers, some cost must be included.

    The manufacturing process and possible entry points for application of the mark

    The transformation of raw materials into finished leather needs a certain number of consecutive operations: chemical, mechanical and thermal. These operations can be gathered in four main phases: beamhouse, tanning, post-tanning and finishing. Bearing in mind these main phases and the easy integration of the marking treatment, two entry points are possible:

    * following post-tanning at the end of the wet-end operations

    * during finishing at the end of the manufacturing process in the dry state

    Certain leather items are often not finished. In order to brand or mark the material, the treatment must include the whole cross section of the leather structure so that the smallest part of a cut element is marked. It is recommended to mark such items at the end of wet operations: this is called marking during the wet-end procedure.

    With regard to leather items that have been finished, the tracer may be incorporated along with the chemical agents (such as film formers on finishing coats): this is known as marking using a dry procedure.

    These two methods were required to be tested using compatible marking systems for both the wet and dry treatments. Both were investigated by CTC.

    Selection criteria according to the chosen tracer

    Depending on the above mentioned methods (dry and wet), some criteria will differ. Common criteria for both methods:

    * very thin grain with maximum particle sizes between 8-10m;

    * the leather as a product must contain no or little colour

    * compatible with the substrate

    * must remain stable with time

    * resistance to mechanical, thermal and chemical operations applied during leather making

    Specific criteria for the wet-end procedure:

    * Soluble product or able to emulsify or disperse in an aqueous environment

    * Product compatible with the chemical agents used prior to its application (such as fatliquors, dyes, retanning agents and formic acid etc)

    * pH stability around 3 to 5

    * Resistance to rinsing pressure (100/200kg per cm2)

    * Thermal resistance when drying (80ºC maximum)

    * Mechanical resistance to glazing, polishing, stretching, milling and staking

    * Stability and resistance to physical-chemical conditions in the finishing process (see following paragraph)

    Specific conditions to the dry procedure:

    * Soluble products or able to disperse in finishing resins (in an aqueous environment or partially soluble)

    * Compatible with finishing agents (such as binders, pigments, touch modifiers etc)

    * Compatible with finishing equipment such as spray lines or rollercoaters

    * Thermal stability (hot air and/or IR) when drying the final film (80-90ºC)

    * Resistance to mechanical and thermal treatments applied to finished leather such as embossing, ironing and hot plating

    In addition to the criteria related to leather and its manufacturing and the end-use, the selection of tracing agents includes other parameters as follows:

    - It is harmless to the consumer

    - Producing an original ID code

    - Ease of applying the identification code in the procedure

    - Access to deciphering the code (for example at the application site or a specialised laboratory)

    - Unforgeable tracing system

    Analysis of the different procedures

    Following a series of initial trials carried out at CTC to find a suitable ID system, the most convincing results were obtained by using three different types of marking or tracing agents:

    1. Procedure based on micro-spheres

    2. Procedure based on DNA synthesis

    3. Procedure using magnetic resonance

    1. Micro-spheres procedure

    This procedure uses micro-spheres with polymeric envelopes with sizes between 2 and 10 microns.

    These micro-spheres present a variety of physical and chemical properties (nature and shape of the envelope) enabling a large application domain in the paper-carton, plastics, glue, ink and varnish, and textile industries. These products are inert, chemically stable and relatively resistant to thermal and mechanical constraints.

    These hollow micro-envelopes are made up of two types of fillers, firstly, a fluorophore agent and secondly a synthetic DNA filler. These have the potential to be used in the industry.

    With regards to the wet-end procedure, a method based on the use of only wet-blue which is then processed into crust and finished leather has been determined. A standard representation of the procedures used in tanneries as well as a control reference has been established and improved for the different test procedures.

    The operating mode has time constraints which were related to drum operations (approximately 4-5 hours of rotation) as well as to those from mechanical and thermal operations carried out on the leather under industrial conditions.

    The analysed parameters included the concentrations of the used tracer, the particle size, the contact time and the position of introduction of wet retanning agents as well as the influence of the final finishing in terms of detection possibilities of the tracer.

    In this type of application, reproducibility is not guaranteed and there are possibilities of contaminating the equipment (for example sammying felts). Also a heavily pigmented finish on the leather makes detection more difficult.

    As in the wet-end procedure, a method with a control has been determined for the analysis of the dry procedure. The application and finishing processes are entirely comparable to those used in the leather industry.

    They make it possible to check beyond the chemical compatibilities of each component, the behaviour of the tracer when applying a spraying gun (application pressure through the spraying valve etc) and mechanical finishing treatments such as ironing or embossing to flatten the grain (pressure and thermal effect).

    The analysed parameters were based on the concentrations used, the finishing types, the size of the particles and their position within the different layers of the finish. This procedure has a good reproducibility and needs relatively lighter concentrations of the tracer.

    There is no risk of contamination and the micro-spheres are resistant to spray gun applications as well as mechanical finishing operations such as ironing and embossing. Additionally, the use of pigments does not interfere in the detection. The process optimisation depends on a balance between particle size and its position within the film.

    2. Process based on DNA synthesis

    DNA synthesis creates the base for a biological marking system with an almost unlimited coding capacity. These procedures are already being applied to banknote paper, perfumes and in general it can be added to all liquid and solid materials. DNA presents the advantage of great safety in terms of marking as well as total security towards the consumer.

    DNA can be used either in its free state directly mixed onto the area to mark or in micro-sphere capsules, particularly when conditions within the environment are less favourable.

    This process has been assessed with a view to its use for leather marking. The blending procedure is carried out with free DNA in a dry state which is mixed with the leather finishing preparation. The analysis of dry DNA has been developed in two ways:

    * Chemical compatibility with the finishing components

    * Application and detection of DNA in finished leather

    It was also necessary to check that leather containing natural DNA in itself was not interfering in the process.

    This analysis has been carried out for the first time and this particular experiment had never been studied before.

    For each case, the compatibility was analysed with the finishing preparations to apply before and after drying and with each component included in these preparations:

    * The DNA mixed with the compounds of acrylic-polyurethane preparations non-dried and polymerised is totally detectable and therefore compatible

    * In semi-aniline finishes of a proteic type, all analysed combinations show compatibility with DNA-finishing resins

    * Compatibility trials with a DNA/nitrocellulose fixation layer have led to positive results in all studied cases. These results give rise to the possibility of marking the surface layers

    Applications on leather have been carried out on semi-aniline and pigmented finished material. In all cases, the tracer concentration was analysed. The following trends were obtained:

    * The mixing of free DNA in proteic and acrylic finishes is completely feasible. Finishes based on polyurethane need further analysis in terms of the extraction of DNA from the dried and polymerised film and compatibility with certain components

    * For companies wishing to mark or brand their products, free DNA marking of finishing films will need further study to check the compatibility between the products used in manufacture and the DNA; certain mechanical operations on finished leather specific to each company will have to be assessed for reproducibility

    * Two level traceability on finished leather is feasible (combining micro-spheres, fluorophore and DNA)

    3. Procedure based on magnetic resonance

    This process is based on an original technique sourced from the magnetic resonance of a material. The marking agent is a preparation made up of a micro-powder that can be mixed in most printing inks or added in the processing of raw ingredients.

    The potential in terms of detection reliability and non-falsification is very good. Current areas where magnetic resonance is used for brand protection include industrial sectors for perfume, wine and spirits, pharmaceutical, banking and other luxury products such as jewels, works of art etc.

    Magnetic resonance detection is carried out through a dedicated portable reader through contact or at a short distance of a few millimetres from the product. The detection readings can be made on the material or product without being physically destructive and monitoring can take place without direct visibility of the surface.

    This labelling system is compatible with other marking/branding technologies thus enabling a tanner or brand to monitor traceability on two levels.

    On the wet-end procedure, CTC noticed a better absorption of the tracer on the reverse (flesh side) of the leather. When thickness is less than or equal to 1.5mm, the detection is possible on the grain side, even if it contains hardly any marking agent. For thicker leathers, the tracer on the side to be monitored needs to be of a sufficient concentration to achieve an accurate result.

    A pigmented finish on leather treated in the wet-end does affect the final detection. With the finishing procedure, CTC found similar conclusions to the ones obtained with micro-spheres: ie the settled tracer quantities were well spread throughout the base coats and pigment finishing layers and were not adversely affected by applying via a spray gun.

    The only point to monitor when using this procedure is the desired distribution of the tracer in the finishing recipe to be added to the leather.

    Conclusion and future investigation

    In order to give a more complete answer for businesses in the leather sector, CTC will endeavour to carry out further analysis. Firstly, marking of pu finishes using free DNA is currently being tested. Secondly, CTC is looking at adding tracer elements to other components used with leather products such as threads and glues etc.

    The initial work which has been presented in this paper requires the acceptance of the three techniques investigated to go through a further validation phase before being commercially ready for use. Settling, compatibility, mixing, blending and detection (direct reading or laboratory analysis) all require further investigation. This involves not only adopting formulations of tracers specific to our industry's needs, but also sometimes the improvement of detection equipment suitable for the characteristics and manufacturing conditions of the treated materials and to those of individual companies.

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 2:36:59 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 2:36:59 PM

    TA.1.18. - Enzymes

    Waterproof leather - requirements and technology - August 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 4:27:19 PM


    Waterproof leathers are commercially of high interest as they are sold at a relatively high price. This higher price level is justified because the processing of waterproof leathers requires a special selection of wet-blue, special products - waterproofing agents and selected retanning, neutralisation and dispersing agents - and special application know-how. In addition, end users are willing to pay high prices for excellent trekking boots for example; therefore, tanneries can demand higher sales revenues compared with standard leather.

    The historical cavalry boot shown is made of Russian leather, which was subsequently impregnated by chrome stearate. This boot is heavy and the foot might get soaked with sweat when worn for a long time. In contrast, the trekking boot is made of state-of-the-art waterproof leather.

    Ramblers can walk quite long distances in these shoes and the feet stay comfortable in spite of perspiration even in the rain, even when walking in a meadow moist with dew, which is a very harsh test for the water resistance of shoes.

    Demands on waterproof leathers

    The aim of processing waterproof leather is the production of leather which has an appealing appearance and results in shoes or motorbike garments etc with high wearing comfort even under wet and cold conditions. Leather should act as a second breathing skin. The skin protects humans against external influences. However, it also allows the body to regulate its temperature by perspiration.

    Waterproof leather literally stands for leather which water doesn't penetrate. However, the leather should allow additionally high water vapour permeability and some reversible water up-take to remove perspiration from the foot. The leather should insulate against heat and cold and be lightweight.

    The common testing procedure for waterproofness - the static tests of the life time of a water droplet, Kubelka water up-take and the soaking up test as requested by membrane shoe manufacturers, as well as the dynamic tests, Bally penetrometer and Maeser value, have to be seen in the context of the use of this leather. For example, a high Maeser value will be requested for an outdoor walking boot as the mechanical action during measurement simulates the mechanical action during walking in water.

    The situation is completely different for outdoor boots which are equipped with a polymeric membrane. For this use excellent water vapour permeability is requested. Furthermore, the leather should not soak up water either from the grain side, the flesh side, or through the cut. Then, the static Wicking-test will be sufficient.

    Likewise, the static water droplet test is sufficient for aniline upholstery leather which is required to be resistant against spilled liquids. Leather which has absorbed too much water, looses its ability to insulate against heat and cold. Therefore, waterproof leather should not take up more than 25-30% of water.

    The dynamic tests Maeser flexometer and Bally penetrometer and their comparability are intricate because - depending upon the customer requirements - different modifications are done. Often the customers' needs deviate from the official testing procedure.

    The read-out can be done electronically - sometimes referred to as 'con luce' - or optically. Electron read-out has a higher degree of rigour, especially when thin leathers are processed. In addition, how demanding a requested value is depends on the processed wet-blue, on the storage time, the degree of olation of the wet-blue and on the thickness of wet-blue.

    For example, 50,000 Maeser flexes are excellent when heavy hides are processed with a thickness higher than 2.5mm due to the strong mechanical action during measurement. This value can mostly be exceeded when leathers of 1.5mm are processed.

    Sometimes certain requirements should be challenged, eg the request for leather which stands more than 100,000 Maeser flexes. A boot made out of this leather would allow a 100km walk in rain. However, it is unlikely that a walker would do that.

    This request might come from the experience that waterproof values sometimes break down after buffing or finishing combined with the need for a reasonable 15-40,000 flexes in the final article. However, in such cases the overall leather production process is wrong and should be revised.

    Figure 1: Internal surface coated with the waterproofing agent

    Figure 2: Openly waterproofed leathers act like a membrane

    Some general thoughts about waterproofing

    If we understand how the wetting of leather takes place, then we will understand more easily how we can slow down or completely prevent this process. The wetting of leather takes place in a four-step process. The water spreads over and wets the leather surface. Then the water penetrates the leather and, thereafter, the water wets the fibre network; in other words, it wets the internal surface of the leather.

    Finally, due to attractive interactions between water and the leather network the leather gets soaked with water. The collagen backbone but also tanning agents, dye molecules, salts etc, which are present in the leather network, might be involved in these interactions.

    This chain of process steps must be interrupted to prevent the wetting of leather. At least one process step must be stopped, which will be explained later.

    A closed waterproof film can be applied in finishing. The spreading of water over the surface is prevented by the film and the leather cannot be wetted at least under static conditions. However, such films even with most modern technologies drastically reduce the water vapour permeability.

    The gaps in the leather can be filled in two completely different ways: firstly, impregnation and secondly, hydrophilic waterproofing. Firstly, impregnation is a treatment of leather by molten waxes. The filling of the gaps with wax prevents the penetration of the water into the fibre network. The disadvantage is that the leather is extremely heavy and completely prevents any air and water vapour permeability.

    Secondly, hydrophilic waterproofing is achieved by application of certain surfactants, eg sulphosuccinates which bind to the leather and make the leather absorb a certain quantity of water. The surfactants and the water form a water-in-oil emulsion, which fill the gaps in the fibre network. Additionally, these micelles are hydrophobic on their outer side and, therefore, the gaps are filled with a hydrophobic material.

    Shoes, which are made of this leather, might have an excellent wearing comfort directly after being put on because the leather is absorbing sweat. However, unfavourably, the leather weight increases drastically. In addition, the breathability of this leather will cease when water has been taken up. Afterwards the shoe will be dried and the water will be removed completely and the leather will return to its original state.

    Open waterproofing

    The so-called open waterproofing is the smartest approach to make waterproof leather. The internal surface of the leather is coated by a waterproof agent that binds to the fibres and fibrils through its functional groups. Waterproof agents are more efficient as the surface tension is lower.

    Figure 1 shows the internal surface schematically coated with the waterproofing agent. Generally all molecules attract each other. The molecule 1, in the interior, is attracted equally from all sides. Overall, no resulting force acts on this molecule. In contrast, the molecule 2, at the surface, is attracted into the interior. As all molecules, which are on the surface, are drawn into the interior, surface energy must be spent to form a surface.

    The larger the surface and the higher the surface tension is, more surface energy must be spent. A very thin coat of the internal surface is formed by waterproofing agents, which have a very low surface tension.

    Glycerides, natural oils, have a surface tension of about 40mN/m and are not appropriate for waterproofing. However, this concept can be realised by waterproofing agents which show a surface tension of about 30mN/m, eg chrome stearates, and hydrophobic esters1 and so-called amphiphilic polymers2, which consist of hydrophilic and hydrophobic parts.

    Silicone-based products allow even thinner coatings of the internal surface due to their low surface tension of 23mN/m. The use of chemically modified silicones materialised at the end of the last millennium. Modified silicones are linear polymers. Functional groups are attached to the backbone through a spacer group at the end of the molecule or randomly as a side chain.

    Münzing modified silicones in their laboratory and noticed during their research that the efficiency of waterproofing agents depends on the molecular weight of the silicone, on the nature and number of functional groups per silicone molecule, on the position of the functional groups in the silicone molecule, but also on the spacer group between functional group and silicone. Although silicones act very efficiently, silicone-free products might be preferable for some articles.

    Lastly, Fluorine chemicals could work even more efficiently, however, due to the extremely high costs, this approach is advisable only in cases when additional requirements are requested.

    Openly waterproof treated leathers act like a membrane (Figure 2). Water vapour can penetrate into the fibre network; however, the 'hydrophilic water' droplets possess a high surface tension and cannot spread over the internal surface and, therefore, the fibres cannot be wetted (Figure 1).

    Water cannot penetrate. Water vapour permeates always from the side with higher water vapour concentration to the reverse side with lower concentration, from the side with higher temperature to the side with lower temperature. Therefore, in hot and humid conditions, for example in a tropical rain forest, waterproof boots loose the ability to emit moisture.

    The open waterproof effect can be visualised by an example from nature. Water striders can walk and jump over water. Their tarsus is covered with numerous fine hydrophobic hairs that cannot submerge allowing the water striders to stay on water. If we put soap into this water, the surface tension of the water would decrease and water striders would sink.

    Similarly, waterproof leather cannot be wetted. However, surfactants cause the leather to be wetted quickly and should be strictly avoided. The lotus-effect, the self-cleaning of the bloom of the lotus in the rain which is commercially used in wall paints and in windscreen care, is based on the same physical fundamentals.

    Actually, the presence of all kinds of hydrophilic substances within the leather might negatively influence the waterproof values of this leather by varying degrees. However, the use of dyes, synthetic and vegetable retanning agents is required to obtain the desired article with a pleasing appearance. Appropriate products and application processes ensure that the hydrophilicity, which is an inherent part of all kinds of leather treatment agents, will be masked in the final article.

    Salts originating from the neutralisation are hydrophilic and, therefore, their presence will increase the water absorption of the final leather article. In addition, during the processing of waterproof leather, these salts might be harmful as they could cause the breaking of the emulsion of the waterproof agent and, hence, prevent even distribution through the cross-section. Consequently, waterproof leather should be washed well after neutralisation.

    Likewise, retanning agents, which are huge and bulky molecules, might influence the waterproof values negatively. Therefore, vegetable tanning agents should be selected carefully. Sweetened vegetable tanning agents have to be strictly avoided because they are even more hydrophilic. Normally synthetic retanning agents cause fewer problems and can be applied in normal quantities. Polyacrylates are flexible molecules, which usually do not harm the waterproofness at all. The hydrophilic parts are supposed to bind to the internal surface, the hydrophobic parts are directed into the gaps of the fibre network.

    Despite their hydrophilicity, certain polymers3 and nitrogen containing aromatic syntans4 support the waterproof effect for several reasons. Firstly, these chemicals are anionic and, therefore, the charge of the cationic wet-blue will be changed into a weakly charged or even anionic substrate.

    In other words the isoelectric point of the leather will be reduced by the presence of syntans and polymers. This is a precondition for the penetration of the anionic waterproofing agents into the inner section of the leather. In addition, specially designed nitrogen containing functional syntans4 support the even distribution of the waterproofing agent through the cross-section due to their dispersing power without negatively affecting the tightness of the wet-blue.

    The use of such products is highly recommended when heavy substance wet-blue is processed, when wet-blue which is not uniform over the hide, when wet-blue from different origins are processed together, or when wet-blue is processed which cannot be neutralised too strongly because the tightness would be negatively affected by strong neutralisation. Likewise, special polymers3 improve the waterproofness as they disperse the waterproofing agents and support the penetration through the cross-section. The use of such polymers in the beginning of the waterproofing step is almost always recommended.

    Figure 3 shows the cross-section of three leathers. All leathers were dyed and waterproof treated according to process 1. The straight curves show the distribution of the silicone-based waterproof agent through the cross-section. The lower leather exhibits the best waterproof performance in terms of water resistance and water vapour permeability because the leather was retanned strongly and the waterproof agent is evenly distributed through the cross-section. The content of silicone is higher in the inner section because here the leather is less anionic than in the outer section and, therefore, there are more potential binding sites for the anionic waterproofing agents. However, this leather might be too soft for shoe upper leather and the grain may be on the loose side depending on the wet-blue origin.

    The upper leather was weakly retanned. Therefore there is a strong cationic zone in the middle of the cross-section. The waterproofing agents were fixed where the penetrating anionic agents met the cationic zone. This leather is tight, however, it is not waterproof and dyed through the cross-section.

    Leathers treated in this way fail the Wicking-test which is of a high importance when leather is foreseen to be a component in membrane lined boots. Water is absorbed through the cut of the test strip up to the arrow when this type of leather is tested. The left strip failed, the right one passed.

    The leather in the middle was retanned in a balanced way and just a thin cationic zone remained. Here, both good waterproofing, water vapour permeability and a tight leather character can be achieved. Due to the higher mechanical action, the dye penetration will be complete in a tannery-scale production.

    The dotted line displays the distribution of silicone-based waterproof agents in leathers that were processed by the modified process 2 which involves two additions of waterproof agent.

    As expected, the achieved waterproofness was even better. It was observed that openly waterproof treated leathers are relaxed and lay flat. Here, the waterproof treatment doesn't cause an area loss, which often takes place when waterproof leathers are processed.


    The production of waterproof leathers showing excellent leather properties and wearing comfort requires both appropriate products and application know-how. Both products and application process must be adapted to the requirements for the final article and to the processed wet-blue. Here, the character of the provenance, the charge and the degree of olation has to be considered.


    The author thanks his colleagues at Münzing Chemie, and mentions Stefan Huster and Wolfgang Eberhardt for their highly committed work and Andreas Waechter for providing the photograph of the water strider.


    1. Ombrellon WR

    2. Ombrellon WD


    4. Development product Ombrellon TAN

    5. Development products Ombrellon 072, Ombrellon 073, Ombrellon 2770

    Usage requirements

    No water penetration

    Controllable water up-take

    High water vapour permeability

    Heat and cold insulation


    Wearing comfort

    Second breathing skin

    Testing requirements

    Water droplet test (IUP/420, EN ISO 15700)

    Kubelka water up-take (IUP/7, EN ISO 2417)

    Soaking-up test (Wicking-test)

    Bally penetrometer (IUP/10, EN IS O 5403)

    Maeser (ASTM D 2099)

    Water vapour permeability (EN ISO 14268)

    Process 1

    Wet-blue, 1.8-2.0mm, US origin

    Neutralisation pH, 5.0, wash well

    Treatment with acrylic polymer3

    Retannage and dyeing4

    Addition silicone based waterproofing agent5

    Fixation/hot water

    Process 2

    Wet-blue, 1.8-2.0mm, US origin

    Neutralisation pH, 5.0, wash well

    Treatment with acrylic polymer3

    First addition silicone based waterproofing agent5

    Retannage and dyeing4

    Second addition silicone based waterproofing agent5

    Fixation/hot water/acid/chrome

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 4:27:19 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 4:27:19 PM

    TA.1.19. - Raw Materials

    Control of halobacterial damage on brine cured hides with halocin - November 2006
    Contributed by: Leather International magazine
    Last updated: 23/09/2008 5:07:32 PM


    Halophilic Archaea of the family Halobacteriaceae are dominant microorganisms in hypersaline environments such as salt lakes, crystalliser ponds of solar salterns, salt mines, hypersaline soda lakes (Grant et al, 1998; Oren 2000). Halophilic Archaea can also grow in artificially salted environments such as salted fish, salted meat, salted hides and certain fermented food products (Thai fish sauce) (Thongthai et al, 1991; Bailey and Birbir 1993; Oren 2000).

    They are easily detected in such habitats since they produce a red to orange pigmentation. These pigments are generally carotenoids which are used to stimulate an active photorepair system to repair thymine dimers formed by ultraviolet radiation (DasSarma and Arora 2001). Extremely halophilic Archaea require at least 1.5-2 M NaCl for growth and optimally most species require 2-4 M NaCl (Grant et al, 2001).

    Although halophilic Archaea produce a wide variety of biotechnological products such as bacteriorhodopsins, halorhodopsins, compatible solutes, biopolymers, biosurfactans, exopolysaccharides, polyhydroxyalkanoates, flavouring agents, isomerases, hydrolases, nucleases, amylases, proteases, lipases, anti-tumour drugs and

    liposomes (Grant et al,1998; Oren 2000; Eichler 2001; Rodriguez-Valera et al, 1991), these organisms may also cause significant damage on brine cured hides (Bailey and Birbir 1993; Birbir and Ilgaz 1996; Birbir et al, 1996; Bitlisli et al, 2004) and salted foods such as fish (Graihoski 1973), meat, cheese, olive, tomato paste, grape leaves and pickles with their hydrolytic enzymes (Birbir et al, 2004a).

    Red heat salted skins. The pictures of red heat were kindly supplied by BLC Leather Technology

    Haloarchaeal damage on hides or skins

    Our earlier studies on halophiles showed that brine cured hides processed in different countries had extremely halophilic Archaea (Bailey and Birbir 1993; Birbir 1997). In the US, 131 brine cured hides were tested for extremely halophilic Archaea and 98% of them contained these microorganisms.

    A total of 332 extremely halophilic Archaeal strains were isolated and 94% of these strains were protease positive (Bailey and Birbir 1993). Moreover, 35 salt-cured French and Russian hides were tested for extremely halophilic microorganisms and 91% of them contained these microorganisms (Birbir 1997).

    From these hides, 85 extremely halophilic strains were isolated and 67% of the strains were protease positive. Furthermore, researchers found that most salted sheepskins contained extremely halophilic Archaea and 53-74% of extremely halophilic Archaea showed proteolytic activity (Bitlisli et al, 2004).

    Presence of proteolytic haloarchaeal strains in salt affect hide quality adversely. Halophilic Archaea can cause discoloration of the flesh side of the skins or hides. This condition is referred to as 'red heat' in the hide industry. This discolouration is due to massive growth of halophilic Archaea (Didato et al, 1999).

    In addition, hair slip or pin prick can be seen on hides that have been inadequately salt packed or brine cured. Proteolytic halophilic Archaea in salt may grow in the hair follicles of hides and cause the degradation of the entire follicle leaving a hole in the grain (Didato et al, 1999). Furthermore, microorganisms grown on hides may cause uneven dyeing in leathers (Bitlisli et al, 2004).

    It was also demonstrated that extremely halophilic Archaea damaged the grain of brine cured hides within seven weeks at a temperature of 41°C. This damage was easily observed by the naked eye and scanning electron microscopy clearly showed that the damage done by halophilic microorganisms resembled sueded grain (Bailey and Birbir 1993). In addition, it was also mentioned that halophilic Archaea caused a complete disruption of collagen fibres and production of sponge-like vesicles within hides (Vreeland et al, 1998).

    Natural antibacterial substances (Bacteriocins)

    Considerable attempts have been made to use bactericides during brine curing of hides (Vivian 1969; Hendry et al, 1971; Birbir and Bailey 2000). Effective bactericides (Birbir and Bailey 2000; Weiss and Thornton 1984; Lollar and Kallenberger 1986; Mitchell 1987) and bile salts (Vreeland and Bailey, 1999) have been recommended to prevent halobacterial damage during brine curing of hides but the use of bactericides have been questioned due to environmental pollution risk, mutation of bacteria and bacterial resistance on repeated uses.

    In recent years, the control of the bacterial population by natural antimicrobial substances is an important alternative to chemicals. It is known that thirty genera of the domain Bacteria produce bacteriocins to inhibit closely related species or even different strains of the same species (Pelczar et al, 1993; Shand 1999). Many of human bacterial flora synthesise and release bacteriocins (Prescott et al, 1993). There are many different bacteriocins including those produced by bacteria normally found in the intestine.

    Bacteriocins may give their producers an adaptive advantage against other bacteria. Sometimes, they may increase bacterial virulence by damaging host cells such as mononuclear phagocytes. Bacteriocin Nisin A produced by the lactic acid bacteria strongly inhibits the growth of a wide range of Gram-positive bacteria and is used as a preservative in food industry (Madigan and Martinko 2006).

    Kwaadsteniet et al (2005) explained that 3944 Da bacteriocin (ST15) produced by Enterococcus mundtii which was isolated from soy beans inhibited the growth of Gram-positive and Gram-negative bacteria such as Lactobacillus sakei, Enterococcus faecalis, Bacillus cereus, Propionibacterium sp, Clostridium tyrobutyricum, Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus caprinus.

    Ghrairi et al, (2005) mentioned that Lactococcin MMT24, which is a novel bacteriocin produced by Lactococcus lactis MMT24, was isolated from a Tunisian traditional cheese. The bacteriocin showed a narrow antimicrobial activity against closely related lactic acid bacteria.

    Oh et al (2006) found that bacteriocin produced by Lactococcus sp HY 449 inhibited the growth of Staphylococcus epidermidis ATCC 12228, Staphylococcus aureus ATCC 65389, Streptococcus pyogenes ATCC 21059 and Propionibacterium acnes ATCC 6919. Researchers explained that the bacteriocin produced by Lactococcus sp. HY 449 might be a useful antimicrobial substance to control the growth of Propioni-bacterium acnes and to prevent skin-inflammation and acne.

    Ammor et al (2006) used 87 lactic acid bacteria (LAB) (36 Lactobacillus sakei, 22 Enterococcus faecium, 16 Lactococcus garvieae, eleven Vagococcus carniphilus and two Enterococcus sp isolated from a small-scale facility producing traditional dry sausages to screen for antagonistic activity against other LAB and some spoilage and pathogenic microorganisms, also isolated from the same processing facility. The main goal of their research was to investigate LAB antibacterial activity within the facility microbial ecosystem and to select interesting strains for the role of bio-preservatives. Twenty-one Enterococcus faecium, six Vagococcus carniphilus, four Lactococcus garvieae, three Lactobacillus sakei and two Enterococcus sp were shown to inhibit the growth of some indicator microorganisms in an agar well diffusion assay. Except two Lactobacillu sakei and an Enterococcus sp, all these isolates exhibited antibacterial activity against Listeria innocua but only three Enterococcus faecium, five Vagococcus carniphilus and three Lactococcus garvieae displayed also antagonistic activity against Staphylococcus aureus. The five Vagococcus carniphilus isolates were also found to be inhibitory for the Gram-negative bacterium Hafnia alvei.

    Sarkar (2006) stated that application of more than one bacteriocin may be advantageous to minimise the possibility of survival of microflora resistant to a particular bacteriocin.

    Natural antibacterial substances (halocins)

    As in domain Bacteria, extremely halophilic Archaeal strains in domain Archaea produce antimicrobial substances called halocins to kill or inhibit other halophilic Archaea in the same or different environmental niche. Researchers have explained that halocin production was a near-universal feature of haloarchaeal rods and, based on antagonism studies, hundreds of different types have been found to exist (Price and Shand 2000). Halocins are natural proteinaceous antimicrobials which were first discovered by Francisco Rodriguez-Valera et al, in 1982. The main reason for the existence of halocins has always been that they reduce competition by lysing competitors and enrich the environment for the producer strains (Rodriguez-Valera et al, 1982). In this research, forty extreme halophiles were screened against each other for production of halocins; seven of forty were found to produce effective halocin against other 39 halobacterial strains. Five of the seven producers inhibited a large number (19 to 35) of the 40 strains, while the remaining two inhibited only a few (1-3) (Rodriguez-Valera et al, 1982).

    In other halocin studies, 147 extremely halophilic strains were screened against each other for production of halocins; 144 of the 147 were found to produce halocins and twenty of the 144 were sensitive to their own halocin and none of the isolates was completely insensitive to all halocin. The results of this study showed that some of the strains inhibited nearly all the strains and the others inhibited only a few. Both studies indicated that there were numerous classes or groups of halocins and the halocin production was a practically universal feature of haloarchaea (Rodriguez-Valera et al, 1982; Meseguer et al, 1986).

    Halocins always reduce competition among haloarchaeal strains (Rodriguez-Valera et al, 1982).

    Liu et al (2003) stated that many species of family Halobacteriaceae produce halocin. They found that halocin C8, excreted by the Halobacterium strain AS7092, had a very wide activity spectrum, including most haloarchaea and even some haloalkaliphilic rods. When a sensitive strain of Halorubrum saccharovorum was exposed to halocin C8, the treated cells swelled at the initial stage. The cell wall appeared to be nicked and the cytoplasm was then extruded out, and the whole cell was eventually completely lysed. They explained that halocin C8 was a novel microhalocin and its primary target might be located in the cell wall of the sensitive cells.

    Haloarchaeal growth on hides may be prevented with natural antimicrobial compounds such as halocins produced by halophilic Archaea. In our halocin study, 56 extremely halophilic archaeal strains isolated from Tuz Lake, Kaldirim saltern, Kayacik saltern and Tuzköy salt mine were screened for antagonistic activity against each other. Twelve of the 19 Tuz Lake strains, twelve of 18 Kaldirim Saltern's strains, five of seven Kayacik Saltern's strains and eight of the twelve Tuzkoy Salt Mine strain were gelatinase positive (Birbir et al, 2004b).

    It was found that seven of the 19 Tuz Lake's strains, sixteen of 18 Kaldirim saltern's strains, two of seven Kayacik saltern's and ten of twelve Tuzköy salt mine's strains produced halocin against each other. Five of the seven Tuz Lake producers inhibited a large number (12-16) of the Tuz Lake's strains, while the remaining two inhibited only a few (1-2).

    The results showed that most of the gelatinase positive strains in Tuz Lake might be inhibited by gelatinase negative strains of Tuz Lake and Kayacik saltern. Three of the sixteen Kaldirim saltern's producers inhibited a large number (9-13) of this saltern's strains, while the remaining thirteen inhibited only a few (1-7). Two of Kayacik saltern's producers inhibited five Kayacik saltern's strains.

    The gelatinase negative strain of Kayacik saltern inhibited all the gelatinase positive strains of this saltern. Five out of ten of the Tuzköy salt mine's products inhibited a large number (6-10) of the Tuzköy salt mine's strains, while the remaining five inhibited only a few (1-4). The results showed that most of the gelatinase positive strains in Tuzköy salt mine might be inhibited by gelatinase negative strains of Tuzköy salt mine and Kayacik saltern strains (Birbir et al, 2004b).

    In conclusion, it was found that gelatinase negative halocin producers inhibited gelatinase positive strains. Therefore, it was suggested that these gelatinase negative halocin producers or their isolated halocins may be used in preventing the proteolytic haloarchaeal damage that can occur during brine curing of hides (Birbir et al, 2004).

    Created by:LANCEY, Ms. Raphaelle 23/09/2008 5:04:51 PM
    Modified by:LANCEY, Ms. Raphaelle 23/09/2008 5:07:32 PM