Tanning , or hide tanning , is the process of treating skins and hides of animals to produce leather . A tannery is the place where the skins are processed.
72-516: Leather is a strong, flexible and durable material obtained from the tanning , or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle , sheep , goats, equine animals, buffalo, pigs and hogs, and aquatic animals such as seals and alligators. Leather can be used to make a variety of items, including clothing, footwear, handbags, furniture, tools and sports equipment, and lasts for decades. Leather making has been practiced for more than 7,000 years and
144-550: A tannery . The English word for tanning is from medieval Latin tannāre , derivative of tannum ( oak bark ), from French tan (tanbark), from old-Cornish tann (oak). These terms are related to the hypothetical Proto-Indo-European * dʰonu meaning ' fir tree'. (The same word is source for Old High German tanna meaning 'fir', related to modern German Tannenbaum ). Ancient civilizations used leather for waterskins , bags, harnesses and tack, boats, armour , quivers , scabbards , boots , and sandals . Tanning
216-441: A bath solution containing vegetable tannins, such as found in gallnuts , the leaves of sumac , the leaves of certain acacia trees, the outer green shells of walnuts , among other plants. The use of vegetable tanning is a process that takes longer than mineral tanning when converting rawhides into leather. Mineral tanned leather is used principally for shoes, car seats, and upholstery in homes (sofas, etc.). Vegetable tanned leather
288-523: A coloring operation. Chemicals added during crusting must be fixed in place. Crusting culminates with a drying and softening operation, and may include splitting, shaving, dyeing , whitening or other methods. For some leathers, tanners apply a surface coating, called "finishing". Finishing operations can include oiling, brushing, buffing, coating, polishing, embossing, glazing , or tumbling , among others. Leather can be oiled to improve its water resistance. This currying process after tanning supplements
360-427: A high content of glycine , proline , and hydroxyproline , usually in the repeat -gly-pro-hypro-gly-. These residues give rise to collagen's helical structure. Collagen's high content of hydroxyproline allows cross-linking by hydrogen bonding within the helical structure. Ionized carboxyl groups (RCO 2 ) are formed by the action of hydroxide. This conversion occurs during the liming process, before introduction of
432-480: A large factor in how hazardous wastewater results in contaminating the environment. This is especially prominent in small and medium-sized tanneries in developing countries. The UN Leather Working Group (LWG) "provides an environmental audit protocol, designed to assess the facilities of leather manufacturers," for "traceability, energy conservation, [and] responsible management of waste products." Untanned hides can be dried and made pliable by rubbing and stretching
504-622: A properly managed facility. A review of the total pollution load decrease achievable according to the United Nations Industrial Development Organization posts precise data on the abatement achievable through industrially proven low-waste advanced methods, while noting, "even though the chrome pollution load can be decreased by 94% on introducing advanced technologies, the minimum residual load 0.15 kg/t raw hide can still cause difficulties when using landfills and composting sludge from wastewater treatment on account of
576-400: A skin at a slaughterhouse, farm, or local fur trader. Before tanning, the skins are often dehaired, then have fat, meat and connective tissue removed. They are then washed and soaked in water with various compounds, and prepared to receive a tanning agent. They are then soaked, stretched, dried, and sometimes smoked. Preparing hides begins by curing them with salt to prevent putrefaction of
648-526: A unique non-creasing characteristic. Because it is made of connective tissue, it is smooth and lacks the pebbled effect of leather derived from animal skin. Horween Leather Company , the oldest tannery in the United States, is known for its production of shell cordovan and was called the "Cordovan capital of the world" by the Chicago Tribune . After removal from the horse, the hide is measured from
720-558: A vat of water and let them deteriorate for months. The mixture would then be placed over a fire to boil off the water to produce glue. A tannery may be associated with a grindery, originally a whetstone facility for sharpening knives and other sharp tools, but later could carry shoemakers ' tools and materials for sale. There are several solid and waste water treatment methodologies currently being researched, such as anaerobic digestion of solid wastes and wastewater sludge. Shell cordovan Shell cordovan, cordovan, or cordwain
792-626: A wet cloth or soaking the leather in water. Various treatments are available such as conditioners . Saddle soap is used for cleaning, conditioning, and softening leather. Leather shoes are widely conditioned with shoe polish . Due to its high resistance to abrasion and wind, leather found a use in rugged occupations. The enduring image of a cowboy in leather chaps gave way to the leather-jacketed and leather-helmeted aviator . When motorcycles were invented, some riders took to wearing heavy leather jackets to protect from road rash and wind blast; some also wear chaps or full leather pants to protect
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#1732848121137864-420: Is a difficult and expensive material to make, and in the late 19th and early 20th century was mostly used for razor strops to hone razors in barber shops. More recently it has been increasingly used for shoes, wallets, and watch straps due to its aesthetic qualities and exceptional durability. It is also used in archery to protect the fingers. It is smooth and durable, ideal for a finger tab . Shell cordovan has
936-503: Is a type of tanned fibrous connective tissue commonly used in high-end shoemaking . Cordovan is an equine material made from the fibrous flat connective tissue (or shell ) beneath the hide on the rump of the horse. The material derives its name from the city of Cordoba, Spain , where it was first produced by the Visigoths in the seventh century, and later also by the Moors . It
1008-530: Is also used for falconry jesses, soccer footwear, (e.g. Adidas Copa Mundial ) and boxing speed bags. Although originally raised for their feathers in the 19th century, ostriches are now more popular for both meat and leather. Ostrich leather has a characteristic "goose bump" look because of the large follicles where the feathers grew. Different processes produce different finishes for many applications, including upholstery, footwear, automotive products, accessories, and clothing. In Thailand , stingray leather
1080-409: Is called bating. Lipases are used in the degreasing operation to hydrolyze fat particles embedded in the skin. Amylases are used to soften skin, to bring out the grain, and to impart strength and flexibility to the skin. These enzymes are rarely used. The natural fibers of leather break down with the passage of time. Acidic leathers are particularly vulnerable to red rot , which causes powdering of
1152-419: Is considered one of the most effective tanning compounds. Chromium-tanned leather can contain between 4 and 5% of chromium. This efficiency is characterized by its increased hydrothermal stability of the skin, and its resistance to shrinkage in heated water. Vegetable tanning uses tannins (a class of polyphenol astringent chemicals), which occur naturally in the bark and leaves of many plants. Tannins bind to
1224-403: Is consistent with cross-linking by polychromium species, of the sort arising from olation and oxolation. Before the introduction of the basic chromium species in tanning, several steps are required to produce a tannable hide. The pH must be very acidic when the chromium is introduced to ensure that the chromium complexes are small enough to fit between the fibers and residues of the collagen. Once
1296-416: Is excellent for use in handbags and garments. After application of the chromium agent, the bath is treated with sodium bicarbonate in the basification process to increase the pH to 3.8–4.0, inducing cross-linking between the chromium and the collagen. The pH increase is normally accompanied by a gradual temperature increase up to 40 °C. Chromium's ability to form such stable bridged bonds explains why it
1368-419: Is not very flexible. It is used for luggage, furniture, footwear, belts, and other clothing accessories. Wet white is a term used for leathers produced using alternative tanning methods that produce an off-white colored leather. Like wet blue, wet white is also a semifinished stage. Wet white can be produced using aldehydes , aluminum, zirconium, titanium, or iron salts, or a combination thereof. Concerns with
1440-450: Is one of the most exploited reptile species in the world in the leather trade. However, it is not endangered and while monitored, trade is legal in most South American countries. Kangaroo leather is used to make items that must be strong and flexible. It is the material most commonly used in bullwhips . Some motorcyclists favor kangaroo leather for motorcycle leathers because of its light weight and abrasion resistance. Kangaroo leather
1512-428: Is preferred. Once bating is complete, the hides and skins are treated by first soaking them in a bath containing common salt (sodium chloride), usually 1 quart of salt to 1 gallon of hot water. When the water cools, one fluid ounce of sulfuric acid is added. Small skins are left in this liquor for 2 days, while larger skins between 1 week and as much as 2 months. In vegetable tanning, the hides are made to soak in
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#17328481211371584-421: Is tawed by soaking in a warm potash alum and salts solution, between 20 and 30 °C (68 and 86 °F). The process increases the hide's pliability, stretchability, softness, and quality. Then, the hide is air dried (crusted) for several weeks, which allows it to stabilize. The use of alum alone for tanning rawhides is not recommended, as it shrinks the surface area of the skin, making it thicker and hard to
1656-420: Is that raw hides dry out to form a hard, inflexible material that, when rewetted, will putrefy , while tanned material dries to a flexible form that does not become putrid when rewetted. Many tanning methods and materials exist. The typical process sees tanners load the hides into a drum and immerse them in a tank that contains the tanning "liquor". The hides soak while the drum slowly rotates about its axis, and
1728-420: Is the characteristic of the keratin class of proteins that gives strength to hair and wools (keratin typically makes up 90% of the dry weight of hair). The hydrogen atoms supplied by the sharpening agent weaken the cystine molecular link whereby the covalent disulfide bond links are ultimately ruptured, weakening the keratin. To some extent, sharpening also contributes to unhairing, as it tends to break down
1800-439: Is used as a leather tanning agent, can cause problems in the kidneys and liver and is also considered a carcinogen . Formaldehyde and arsenic, which are used for leather finishing, cause health problems in the eyes, lungs, liver, kidneys, skin, and lymphatic system and are also considered carcinogens. The waste from leather tanneries is detrimental to the environment and the people who live in it. The use of old technologies plays
1872-461: Is used in leather crafting and in making small leather items, such as wallets, handbags and clothes. Chromium(III) sulfate ( [Cr(H 2 O) 6 ] 2 (SO 4 ) 3 ) has long been regarded as the most efficient and effective tanning agent. Chromium(III) compounds of the sort used in tanning are significantly less toxic than hexavalent chromium , although the latter arises in inadequate waste treatment. Chromium(III) sulfate dissolves to give
1944-545: Is used in wallets and belts. Stingray leather is tough and durable. The leather is often dyed black and covered with tiny round bumps in the natural pattern of the back ridge of an animal. These bumps are then usually dyed white to highlight the decoration. Stingray rawhide is also used as grips on Chinese swords, Scottish basket hilted swords, and Japanese katanas . Stingray leather is also used for high abrasion areas in motorcycle racing leathers (especially in gloves, where its high abrasion resistance helps prevent wear through in
2016-403: The "front" is typically used in the fabrication of gloves , or blackened, to be used in the tops of shoes. The "butt", after tanning, is passed through a splitting-machine which removes the grain, or hair side, revealing what is termed the "shell". The close fibers of the shell result in a smooth and pliable material used mostly in the manufacture of shoes . Other uses include watch straps and
2088-588: The 1970s and 80s) are well known for wearing leather clothing. Extreme metal bands (especially black metal bands) and Goth rock groups have extensive black leather clothing. Leather has become less common in the punk community over the last three decades, as there is opposition to the use of leather from punks who support animal rights . Many cars and trucks come with optional or standard leather or "leather faced" seating. In countries with significant populations of individuals observing religions which place restrictions on material choices, vendors typically clarify
2160-411: The adoption in medicine of soaking gut sutures in a chromium (III) solution after 1840, it was discovered that this method could also be used with leather and thus was adopted by tanners. The tanning process begins with obtaining an animal skin. When an animal skin is to be tanned, the animal is killed and skinned before the body heat leaves the tissues. This can be done by the tanner, or by obtaining
2232-408: The bark of certain trees, in the production of leather. An alternative method, developed in the 1800s, is chrome tanning, where chromium salts are used instead of natural tannins. Tanning hide into leather involves a process which permanently alters the protein structure of skin, making it more durable and less susceptible to decomposition and coloring. The place where hides are processed is known as
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2304-485: The case of Bangladesh, chickens (the nation's most common source of protein). Up to 25% of the chickens in Bangladesh contained harmful levels of hexavalent chromium, adding to the national health problem load. Chromium is not solely responsible for these diseases. Methylisothiazolinone , which is used for microbiological protection (fungal or bacterial growth), causes problems with the eyes and skin. Anthracene , which
2376-436: The collagen from bacterial growth during the time lag from procuring the hide to when it is processed. Curing removes water from the hides and skins using a difference in osmotic pressure. The moisture content of hides and skins is greatly reduced, and osmotic pressure increased, to the point that bacteria are unable to grow. In wet-salting, the hides are heavily salted, then pressed into packs for about 30 days. In brine -curing,
2448-459: The collagen proteins in the hide and coat them, causing them to become less water-soluble and more resistant to bacterial attack. The process also causes the hide to become more flexible. The primary barks processed in bark mills and used in modern times are chestnut , oak , redoul , tanoak , hemlock , quebracho , mangrove , wattle (acacia; see catechol ), and myrobalans from Terminalia spp., such as Terminalia chebula . In Ethiopia ,
2520-416: The collagen's carboxyl groups, amine groups from the side chains of the amino acids , and masking agents. Masking agents are carboxylic acids , such as acetic acid , used to suppress formation of polychromium(III) chains. Masking agents allow the tanner to further increase the pH to increase collagen's reactivity without inhibiting the penetration of the chromium(III) complexes. Collagen is characterized by
2592-540: The combined vegetable oils of Niger seed ( Guizotia abyssinica ) and flaxseeds were used in treating the flesh side of the leather, as a means of tawing, rather than of tanning. In Yemen and Egypt , hides were tanned by soaking them in a bath containing the crushed leaves and bark of the Salam acacia (Acacia etbaica; A. nilotica kraussiana). Hides that have been stretched on frames are immersed for several weeks in vats of increasing concentrations of tannin. Vegetable-tanned hide
2664-409: The desired level of penetration of chrome into the substance is achieved, the pH of the material is raised again to facilitate the process. This step is known as basification. In the raw state, chrome-tanned skins are greyish-blue, so are referred to as wet blue . Chrome tanning is faster than vegetable tanning (taking less than a day for this part of the process) and produces a stretchable leather which
2736-425: The end use of the leather, hides may be treated with enzymes to soften them, a process called bating . In modern tanning, these enzymes are purified agents, and the process no longer requires bacterial fermentation (as from dung-water soaking) to produce them. Pickling is another term for tanning, or what is the modern equivalent of turning rawhide into leather by the use of modern chemical agents, if mineral tanning
2808-676: The event of an accident). For a given thickness, fish leather is typically much stronger due to its criss-crossed fibers. Leather produces some environmental impact, most notably due to: Estimates of the carbon footprint of bovine leather range from 65 to 150 kg of CO 2 equivalent per square meter of production. One ton of hide or skin generally produces 20 to 80 m of waste water, including chromium levels of 100–400 mg/L, sulfide levels of 200–800 mg/L, high levels of fat and other solid wastes, and notable pathogen contamination. Producers often add pesticides to protect hides during transport. With solid wastes representing up to 70% of
2880-562: The fibers with a hide stretcher, and fatting. However the hide will revert to rawhide if not periodically replenished with fat or oil, especially if it gets wet. Many Native Americans of the arid western regions wore clothing made by this process. Smoke tanning is listed among the conventional methods like chrome tanning and vegetable tanning. Impregnation of the hide's cells with formaldehyde (from smoke) offers some microbial and water resistance. Leftover leather would historically be turned into glue . Tanners would place scraps of hides in
2952-446: The following grades: The term "genuine leather" does not describe a specific grade. The term often indicates split leather that has been extensively processed, and some sources describe it as synonymous with bicast leather, or made from multiple splits glued together and coated. In some countries, when it is the description on a product label the term means nothing more than "contains leather"; depending on jurisdiction, regulations limit
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3024-418: The hair proteins. The isoelectric point of the collagen (a tissue-strengthening protein unrelated to keratin) in the hide is also shifted to around pH 4.7 due to liming. Any hairs remaining after liming are removed mechanically by scraping the skin with a dull knife, a process known as scudding. The pH of the collagen is then reduced so the enzymes may act on it in a process known as deliming. Depending on
3096-406: The hexaaquachromium(III) cation, [Cr(H 2 O) 6 ] , which at higher pH undergoes processes called olation to give polychromium(III) compounds that are active in tanning, being the cross-linking of the collagen subunits. The chemistry of [Cr(H 2 O) 6 ] is more complex in the tanning bath rather than in water due to the presence of a variety of ligands. Some ligands include the sulfate anion,
3168-447: The hide is prepared for tanning. Preparatory stages may include soaking, hair removal, liming , deliming , bating , bleaching , and pickling . Tanning is a process that stabilizes the proteins , particularly collagen , of the raw hide to increase the thermal, chemical and microbiological stability of the hides and skins, making it suitable for a wide variety of end applications. The principal difference between raw and tanned hides
3240-459: The hides are agitated in a saltwater bath for about 16 hours. Curing can also be accomplished by preserving the hides and skins at very low temperatures. The steps in the production of leather between curing and tanning are collectively referred to as beamhouse operations. They include, in order, soaking, liming , removal of extraneous tissues (unhairing, scudding and fleshing), deliming , bating or puering, drenching, and pickling. In soaking,
3312-406: The hides are soaked in clean water to remove the salt left over from curing and increase the moisture so that the hide or skin can be further treated. To prevent damage of the skin by bacterial growth during the soaking period, biocides , typically dithiocarbamates , may be used. Fungicides such as TCMTB may also be added later in the process, to protect wet leathers from mold growth. After 1980,
3384-486: The leading producers of leather today are China and India. Critics of tanneries claim that they engage in unsustainable practices that pose health hazards to the people and the environment near them. The leather manufacturing process is divided into three fundamental subprocesses: preparatory stages, tanning, and crusting. A further subprocess, finishing, can be added into the leather process sequence, but not all leathers receive finishing. The preparatory stages are when
3456-440: The leather. Chemical damage can also occur from exposure to environmental factors, including ultraviolet light, ozone, acid from sulfurous and nitrous pollutants in the air, or through a chemical action following any treatment with tallow or oil compounds. Both oxidation and chemical damage occur faster at higher temperatures. There are few methods to maintain and clean leather goods properly such as using damp cloth and avoid using
3528-480: The lower body. Leather's flexibility allows it to be formed and shaped into balls and protective gear. Subsequently, many sports use equipment made with leather, such as baseball gloves and the ball used in cricket and gridiron football . Leather fetishism is the name popularly used to describe a fetishistic attraction to people wearing leather, or in certain cases, to the garments themselves. Many rock groups (particularly heavy metal and punk groups in
3600-399: The natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil , neatsfoot oil , or a similar material keeps it supple and improves its lifespan dramatically. Tanning processes largely differ in which chemicals are used in the tanning liquor. Some common types include: In general, leather is produced in
3672-427: The outskirts of town, among the poor. Tanning by ancient methods is so foul-smelling that tanneries are still isolated from those towns today where the old methods are used. Skins typically arrived at the tannery dried stiff and dirty with soil and gore. First, the ancient tanners would soak the skins in water to clean and soften them. Then they would pound and scour the skin to remove any remaining flesh and fat . Hair
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#17328481211373744-508: The process. Chemicals used in tanned leather production increase the levels of chemical oxygen demand and total dissolved solids in water when not disposed of responsibly. These processes also use large quantities of water and produce large amounts of pollutants. Boiling and sun drying can oxidize and convert the various chromium(III) compounds used in tanning into carcinogenic hexavalent chromium , or chromium(VI). This hexavalent chromium runoff and scraps are then consumed by animals, in
3816-529: The regulations currently in force in some countries." In Kanpur , the self-proclaimed "Leather City of World"—with 10,000 tanneries as of 2011 and a city of three million on the banks of the Ganges —pollution levels were so high, that despite an industry crisis, the pollution control board decided to shut down 49 high-polluting tanneries out of 404 in July 2009. In 2003 for instance, the main tanneries' effluent disposal unit
3888-443: The root of the tail 18 inches forward on the backbone . The hide is cut at right angles to the backbone and the resulting pieces termed a "front" (the forward part) and the "butt". The term cordovan leather applies to the product of both the tanned fronts and tanned butts, but is especially used in connection with the term galoshes , meaning the vamps or boot -fronts cut from the shell of the butt. After being tanned, leather from
3960-468: The shell. It is prized for its mirror-like finish and anti-creasing properties. Lamb and deerskin are used for soft leather in more expensive apparel. Deerskin is widely used in work gloves and indoor shoes. Reptilian skins, such as alligator , crocodile, and snake , are noted for their distinct patterns that reflect the scales of their species. This has led to hunting and farming of these species in part for their skins. The Argentine black and white tegu
4032-536: The source of leather in their products. Such labeling helps facilitate religious observance, so, for example, a Muslim will not accidentally purchase pigskin or a Hindu can avoid cattleskin. Such taboos increase the demand for religiously neutral leathers such as ostrich and deer . Judaism forbids the comfort of wearing leather shoes on Yom Kippur , Tisha B'Av , and during mourning. Also, see Leather in Judaism , Teffilin and Torah Scroll . Jainism prohibits
4104-400: The surface and a change in consistency. Damage from red rot is aggravated by high temperatures and relative humidities. Although it is chemically irreversible, treatments can add handling strength and prevent disintegration of red rotted leather. Exposure to long periods of low relative humidities (below 40%) can cause leather to become desiccated, irreversibly changing the fibrous structure of
4176-403: The tanning agent (chromium salts). Later during pickling, collagen carboxyl groups are temporarily protonated for ready transport of chromium ions. During basification step of tanning, the carboxyl groups are ionized and coordinate as ligands to the chromium(III) centers of the oxo-hydroxide clusters. Tanning increases the spacing between protein chains in collagen from 10 to 17 Å. The difference
4248-438: The tanning liquor slowly penetrates through the full thickness of the hide. Once the process achieves even penetration, workers slowly raise the liquor's pH in a process called basification, which fixes the tanning material to the leather. The more tanning material fixed, the higher the leather's hydrothermal stability and shrinkage temperature resistance. Crusting is a process that thins and lubricates leather. It often includes
4320-436: The term's use in product labelling. Today, most leather is made of cattle (cow) hides, which constitute about 65% of all leather produced. Other animals that are used include sheep (about 13%), goats (about 11%), and pigs (about 10%). Obtaining accurate figures from around the world is difficult, especially for areas where the skin may be eaten. There are significant regional differences in leather production: i.e. goat leather
4392-407: The touch. If alum is applied to the fur, it makes the fur dull and harsh. Depending on the finish desired, the leather may be waxed, rolled, lubricated, injected with oil, split, shaved, or dyed. The tanning process involves chemical and organic compounds that can have a detrimental effect on the environment. Agents such as chromium, vegetable tannins, and aldehydes are used in the tanning step of
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#17328481211374464-492: The toxicity and environmental impact of any chromium (VI) that may form during the tanning process have led to increased research into more efficient wet white methods. The conditions present in bogs, including highly acidic water, low temperature, and a lack of oxygen, combine to preserve but severely tan the skin of bog bodies . Tawing is a method that uses alum and other aluminium salts , generally in conjunction with binders such as egg yolk, flour, or other salts. The hide
4536-418: The use of pentachlorophenol and mercury -based biocides and their derivatives was forbidden. After soaking, the hides are treated with milk of lime (a basic agent) typically supplemented by "sharpening agents" (disulfide reducing agents) such as sodium sulfide , cyanides , amines , etc. This: The weakening of hair is dependent on the breakdown of the disulfide link of the amino acid cystine , which
4608-742: The use of leather, since it is obtained by killing animals. Many forms of artificial leather have been developed, usually involving polyurethane or vinyl coatings applied to a cloth backing. Many names and brands for such artificial leathers exist, including "pleather", a portmanteau of "plastic leather", and the brand name Naugahyde . Another alternative is cultured leather which is lab-grown using cell-culture methods, mushroom-based materials and gelatin-based textile made by upcycling meat industry waste. Leather made of fungi or mushroom-based materials are completely biodegradable. Tanning (leather) Historically, vegetable based tanning used tannin , an acidic chemical compound derived from
4680-455: The weekend of 8 April 2017 in the neighborhood. The higher cost associated with the treatment of effluents than to untreated effluent discharging leads to illegal dumping to save on costs. For instance, in Croatia in 2001, proper pollution abatement cost US$ 70–100 per ton of raw hides processed against $ 43/t for irresponsible behavior. In November 2009, one of Uganda's main leather making companies
4752-720: The wet weight of the original hides, the tanning process represents a considerable strain on water treatment installations. Leather biodegrades slowly—taking 25 to 40 years to decompose . However, vinyl and petrochemical-derived materials take 500 or more years to decompose. Tanning is especially polluting in countries where environmental regulations are lax, such as in India, the world's third-largest producer and exporter of leather. To give an example of an efficient pollution prevention system, chromium loads per produced tonne are generally abated from 8 kg to 1.5 kg. VOC emissions are typically reduced from 30 kg/t to 2 kg/t in
4824-419: Was a fermentative process that relied on enzymes produced by bacteria found in the dung. Among the kinds of dung commonly used were those of dogs or pigeons. Historically the actual tanning process used vegetable tanning. In some variations of the process, cedar oil , alum , or tannin was applied to the skin as a tanning agent. As the skin was stretched, it would lose moisture and absorb the agent. Following
4896-523: Was being carried out by the inhabitants of Mehrgarh in Pakistan between 7000 and 3300 BCE. Around 2500 BCE , the Sumerians began using leather, affixed by copper studs , on chariot wheels . The process of tanning was also used for boats and fishing vessels: ropes, nets, and sails were tanned using tree bark. Formerly, tanning was considered a noxious or "odoriferous trade" and relegated to
4968-543: Was caught directly dumping waste water into a wetland adjacent to Lake Victoria . Enzymes like proteases , lipases , and amylases have an important role in the soaking, dehairing, degreasing, and bating operations of leather manufacturing. Proteases are the most commonly used enzymes in leather production. The enzyme must not damage or dissolve collagen or keratin , but should hydrolyze casein , elastin , albumin , globulin -like proteins, and nonstructural proteins that are not essential for leather making. This process
5040-574: Was dumping 22 tonnes of chromium-laden solid waste per day in the open. In the Hazaribagh neighborhood of Dhaka in Bangladesh , chemicals from tanneries end up in Dhaka's main river. Besides the environmental damage, the health of both local factory workers and the end consumer is also negatively affected. After approximately 15 years of ignoring high court rulings, the government shut down more than 100 tanneries
5112-545: Was historically called "Turkey" or "Morocco" due to its association with the Middle East, while pig skin had historically been used the most in Germany. Other animals mentioned below only constitute a fraction of a percent of total leather production. Horse hides are used to make particularly durable leathers. Shell cordovan is a horse leather made not from the outer skin but from an under layer, found only in equine species, called
5184-424: Was removed by soaking the skin in urine , painting it with an alkaline lime mixture, or simply allowing the skin to putrefy for several months then dipping it in a salt solution. After the hair was loosened, the tanners scraped it off with a knife. Once the hair was removed, the tanners would " bate " (soften) the material by pounding dung into the skin, or soaking the skin in a solution of animal brains. Bating
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