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Leather is a strong, flexible and durable material obtained from the
tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...
, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
,
sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...
, goats,
equine Equinae is a subfamily of the family Equidae, which have lived worldwide (except Indonesia and Australia) from the Hemingfordian stage of the Early Miocene (16 million years ago) onwards. They are thought to be a monophyletic grouping.B. J. MacFa ...
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 the leading producers of leather today are China and India. Animal rights groups claim that modern commercial leather making and the consumption of its products is unethically killing animals. According to the life-cycle assessment (LCA) report for the United Nations Industrial Development Organization, 99% of the raw hides and skins used in the production of leather derive from animals raised for meat and/or dairy production. Critics of
tanneries Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...
claim that they engage in unsustainable practices that pose health hazards to the people and the environment near them. The processing stages of tanneries use thousands of liters of water for one hide or animal skin and release toxic liquid waste into the environment that can cause soil depletion and health issues related to the human skin, respiratory system and more. However, advancements have been made in the amount and treatment of water used by tanneries to reduce impact.


Production processes

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 the hide is prepared for tanning. Preparatory stages may include soaking, hair removal, liming,
deliming The deliming operation in leather processing is a drum/paddle or pit based operation where two main objectives are met: * Removal of alkali from the pelt and the consequent deswelling of the fibres. * Lowering of the liquor pH to the values used i ...
, bating,
bleaching Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...
, and
pickling Pickling is the process of preserving or extending the shelf life of food by either anaerobic fermentation in brine or immersion in vinegar. The pickling procedure typically affects the food's texture and flavor. The resulting food is called a ...
.
Tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...
is a process that stabilizes the
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, particularly
collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
, 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 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 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 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 Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular ...
, 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 In mathematics and computer science, currying is the technique of translating the evaluation of a function that takes multiple arguments into evaluating a sequence of functions, each with a single argument. For example, currying a function f that ...
process after tanning supplements 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 Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...
,
neatsfoot oil Neatsfoot oil is a yellow oil rendered and purified from the shin bones and feet (but not the hooves) of cattle. "Neat" in the oil's name comes from an Old English word for cattle. Neatsfoot oil is used as a conditioning, softening and preserva ...
, or a similar material keeps it supple and improves its lifespan dramatically.


Tanning methods

Tanning processes largely differ in which chemicals are used in the tanning liquor. Some common types include: * is tanned using
tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'', ...
s extracted from
vegetable matter Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
, such as tree
bark Bark may refer to: * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, ...
prepared in
bark mill Bark mills, also known as Catskill's mills, are water, steam, horse, ox or wind-powered edge mills used to process the bark, roots, and branches of various tree species into a fine powder known as tanbark, used for tanning leather. This powderin ...
s. It is the oldest known method. It is supple and light brown in color, with the exact shade depending on the mix of materials and the color of the skin. The color tan derives its name from the appearance of undyed vegetable-tanned leather. Vegetable-tanned leather is not stable in water; it tends to discolor, and if left to soak and then dry, it shrinks and becomes harder, a feature of vegetable-tanned leather that is exploited in traditional shoemaking. In hot water, it shrinks drastically and partly congeals, becoming rigid and eventually brittle.
Boiled leather Boiled leather, often referred to by its French translation, cuir bouilli (), was a historical material common in the Middle Ages and Early Modern Period and used for various purposes. It was leather that had been treated so that it became tough ...
is an example of this, where the leather has been hardened by being immersed in boiling water, or in
wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give low ...
or similar substances. Historically, it was occasionally used as
armor Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or fr ...
after hardening, and it has also been used for
book binding Bookbinding is the process of physically assembling a book of codex format from an ordered stack of ''signatures'', sheets of paper folded together into sections that are bound, along one edge, with a thick needle and strong thread. Cheaper, b ...
. * Chrome-tanned leather is tanned using chromium sulfate and other
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
s. It is also known as "wet blue" for the pale blue color of the undyed leather. The chrome tanning method usually takes approximately one day to complete, making it best suited for large-scale industrial use. This is the most common method in modern use. It is more supple and pliable than vegetable-tanned leather and does not discolor or lose shape as drastically in water as vegetable-tanned. However, there are environmental concerns with this tanning method, as chromium is a heavy metal; while the trivalent chromium used for tanning is harmless, other byproducts can contain toxic variants. The method was developed in the latter half of the 19th century as tanneries wanted to find ways to speed up the process and to make leather more waterproof. * Aldehyde-tanned leather is tanned using
glutaraldehyde Glutaraldehyde is an organic compound with the formula . The molecule consists of a five carbon chain doubly terminated with formyl (CHO) groups. It is usually used as a solution in water, and such solutions exists as a collection of hydrates, c ...
or
oxazolidine An oxazolidine is a five-membered ring compound consisting of three carbon atoms, a nitrogen atom and an oxygen atom. The O atom and NH group are the 1 and 3 positions, respectively. In oxazolidine derivatives, there is always a carbon atom betwee ...
compounds. It is referred to as "wet white" due to its pale cream color. It is the main type of "chrome-free" leather, often seen in shoes for infants and automobiles.
Formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
has been used for tanning in the past; it is being phased out due to danger to workers and sensitivity of many people to formaldehyde. **
Chamois leather Chamois leather () is a type of porous leather, traditionally the skin of the chamois (''Rupicapra rupicapra''), a type of European mountain goat, but today made almost exclusively from the flesh split of a sheepskin. United Kingdom The Brit ...
is a form of aldehyde tanning that produces a porous and highly water-absorbent leather. Chamois leather is made using oil (traditionally cod oil) that oxidize to produce the aldehydes that tan the leather. * Brain tanned leathers are made by a labor-intensive process that uses emulsified oils, often those of animal brains such as deer, cattle, and buffalo. They are known for their exceptional softness and washability. * Alum leather is transformed using
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
salts mixed with a variety of binders and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
sources, such as flour and egg yolk. Alum leather is not actually tanned; rather the process is called "tawing", and the resulting material reverts to rawhide if soaked in water long enough to remove the alum salts.


Grades

In general, leather is produced in the following grades: * Top-grain leather includes the outer layer of the hide, known as the grain, which features finer, more densely packed fibers, resulting in strength and durability. Depending on thickness, it may also contain some of the more fibrous under layer, known as the corium. Types of top-grain leather include: **Full-grain leather contains the entire grain layer, without any removal of the surface. Rather than wearing out, it develops a
patina Patina ( or ) is a thin layer that variously forms on the surface of copper, brass, bronze and similar metals and metal alloys (tarnish produced by oxidation or other chemical processes) or certain stones and wooden furniture (sheen produced b ...
during its useful lifetime. It is usually considered the highest quality leather. Furniture and footwear are often made from full-grain leather. Full-grain leather is typically finished with a soluble
aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...
dye.
Russia leather Russia leather is a particular form of bark-tanned cow leather. It is distinguished from other types of leather by a processing step that takes place after tanning, where birch oil is worked into the rear face of the leather. This produces a leather ...
is a form of full-grain leather. ** Corrected grain leather has the surface subjected to finishing treatments to create a more uniform appearance. This usually involves buffing or sanding away flaws in the grain, then dyeing and embossing the surface. **
Nubuck Nubuck (pronounced ) is top-grain leather that has been sanded or buffed on the grain side, or outside, to give a slight nap of short protein fibers, producing a velvet-like surface. It is resistant to wear, and may be white or coloured. Nubuck ...
is top-grain leather that has been sanded or buffed on the grain side to give a slight nap of short protein fibers, producing a velvet-like surface. * Split leather is created from the corium left once the top-grain has been separated from the hide, known as the drop split. In thicker hides, the drop split can be further split into a middle split and a flesh split. **
Bicast leather Bicast leather (also spelled as bi-cast leather or bycast leather) is a material made with a split leather backing covered with an embossed layer of polyurethane or vinyl. Bicast leather was originally made for the apparel industry for glossy shoe ...
is split leather that is pressed into a wet layer of
polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...
or
vinyl Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from vinyl m ...
on embossed
release paper A release liner or ''release paper'' is a paper or plastic-based film sheet (usually applied during the manufacturing process) used to prevent a sticky surface from prematurely adhering. It is coated on one or both sides with a release agent, whic ...
, then cured. This gives it the appearance of a grain. It is slightly stiffer than top-grain leather but has a more consistent texture. **
Patent leather Patent leather is a type of coated leather that has a high-gloss finish. The coating process was introduced to the United States and improved by inventor Seth Boyden, of Newark, New Jersey, in 1818, with commercial manufacture beginning Septemb ...
is leather that has been given a high-gloss finish by the addition of a coating. Dating to the late 1700s, it became widely popular after inventor
Seth Boyden Seth Boyden (November 17, 1788 – March 31, 1870) was an American inventor. Early life He was born in Foxboro, Massachusetts, on November 17, 1788, the son of Seth Boyden and Susannah Atherton. His father was a farmer and blacksmith. His yo ...
developed the first mass-production process, using a linseed-oil-based lacquer, in 1818. Modern versions are usually a form of bicast leather. **
Suede Suede (pronounced ) is a type of leather with a fuzzy, napped finish, commonly used for jackets, shoes, fabrics, purses, furniture, and other items. The term comes from the French , which literally means "gloves from Sweden". The term was fir ...
is made from the underside of a split to create a soft, napped finish. It is often made from younger or smaller animals, as the skins of adults often result in a coarse, shaggy nap. *Genuine leather is a term with many definitions. In some countries, when it is the description on a product label the term means nothing more than "contains leather". The term often indicates split leather that has been extensively processed, which is not considered a high-quality product. Some sources describe it as synonymous with bicast leather, or made from multiple splits glued together and painted, or even bonded leather. In some countries regulations limit the term's use in product labelling. *
Bonded leather Bonded leather, also called reconstituted leather, composition leather or blended leather, is a term used for a manufactured upholstery material which contains animal hide. It is made as a layered structure of a fiber or paper backer covered with ...
, also called ''reconstituted leather'', is a material that uses leather scraps that are shredded and bonded together with polyurethane or
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
onto a fiber mesh. The amount of leather fibers in the mix varies from 10% to 90%, affecting the properties of the product.


From other animals

Today, most leather is made of
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
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. 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 Shell cordovan or cordovan is a type of leather commonly used in high-end shoemaking. Cordovan is an equine leather made from the fibrous flat connective tissue (or ''shell'') beneath the hide on the rump of the horse. The leather derives its nam ...
is a horse leather made not from the outer skin but from an under layer, found only in equine species, called 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 An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additiona ...
, crocodile, and
snake Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
, 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 The Argentine black and white tegu (''Salvator merianae''), also known as the Argentine giant tegu, the black and white tegu, the huge tegu, is a species of lizard in the Family (biology), family Teiidae. The species is the largest of the "tegu l ...
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 Kangaroo leather is a strong light weight leather derived from the hide of the kangaroo. Kangaroos are harvested. Both the meat and the hides are sold. Although hunting most species of macropod is prohibited, a small number of the large-sized ...
is used to make items that must be strong and flexible. It is the material most commonly used in
bullwhip A bullwhip is a single-tailed whip, usually made of braided leather or nylon, designed as a tool for working with livestock or competition. Bullwhips are pastoral tools, traditionally used to control livestock in open country. A bullwhip's leng ...
s. Some
motorcyclists Motorcycling is the act of riding a motorcycle. For some people, motorcycling may be the only affordable form of individual motorized transportation, and small-displacement motorcycles are the most common motor vehicle in the most populous co ...
favor kangaroo leather for
motorcycle leathers A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising, ...
because of its light weight and abrasion resistance. Kangaroo leather is also used for falconry jesses, soccer footwear, (e.g.
Adidas Copa Mundial The Adidas Copa Mundial (Spanish for ''World Cup'') is a football boot manufactured by multinational corporation Adidas and released in 1979.
) and boxing speed bags. Although originally raised for their feathers in the 19th century,
ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
es are now more popular for both meat and leather.
Ostrich leather Bag «Classic» Braun. Ostrich leather is the result of tanning skins taken from African ostriches farmed for their feathers, skin and meat. The leather is distinctive for its pattern of bumps or vacant quill follicles, ranged across a smooth fie ...
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 Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
,
stingray Stingrays are a group of sea rays, which are cartilaginous fish related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae ( ...
leather is used in
wallets A wallet is a flat case or pouch often used to carry small personal items such as paper currency, credit cards; identification documents such as driver's license, identification card, club card; photographs, transit pass, business cards and oth ...
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
katana A is a Japanese sword characterized by a curved, single-edged blade with a circular or squared guard and long grip to accommodate two hands. Developed later than the ''tachi'', it was used by samurai in feudal Japan and worn with the edge fa ...
s. 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 the event of an accident). For a given thickness, fish leather is typically much stronger due to its criss-crossed fibers.


Environmental impact

Leather produces some environmental impact, most notably due to: * The carbon footprint of cattle rearing (see
environmental impact of meat production The environmental impact of meat production varies because of the wide variety of agricultural practices employed around the world. All agricultural practices have been found to have a variety of effects on the environment. Some of the environmen ...
) * Use of chemicals in the tanning process (e.g.,
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
,
phthalate esters Phthalates (, ), or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften ...
, nonyl phenol ethoxylate soaps,
pentachlorophenol Pentachlorophenol (PCP) is an organochlorine compound used as a pesticide and a disinfectant. First produced in the 1930s, it is marketed under many trade names. It can be found as pure PCP, or as the sodium salt of PCP, the latter of which diss ...
and
solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s) * Air pollution due to the transformation process (
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
is formed during mixing with acids and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
liberated during deliming, solvent vapors)


Carbon footprint

Estimates of the
carbon footprint A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
of bovine leather range from 65 to 150 kg of CO2 equivalent per square meter of production.


Water footprint

One ton of hide or skin generally produces 20 to 80 m3 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 the wet weight of the original hides, the tanning process represents a considerable strain on water treatment installations.


Disposal

Leather
biodegrade Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
s slowly—taking 25 to 40 years to
decompose Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...
. However, vinyl and petrochemical-derived materials take 500 or more years to decompose.


Chemical waste disposal

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 VOC, VoC or voc may refer to: Science and technology * Open-circuit voltage (VOC), the voltage between two terminals when there is no external load connected * Variant of concern, a category used during the assessment of a new variant of a virus ...
emissions are typically reduced from 30 kg/t to 2 kg/t in a properly managed facility. A review of the total pollution load decrease achievable according to the
United Nations Industrial Development Organization The United Nations Industrial Development Organization (UNIDO) (French: Organisation des Nations unies pour le développement industriel; French/Spanish acronym: ONUDI) is a specialized agency of the United Nations that assists countries in e ...
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 the regulations currently in force in some countries." In
Kanpur Kanpur or Cawnpore ( /kɑːnˈpʊər/ pronunciation (help·info)) is an industrial city in the central-western part of the state of Uttar Pradesh, India. Founded in 1207, Kanpur became one of the most important commercial and military stations o ...
, 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 The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
—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 was dumping 22 tonnes of chromium-laden solid waste per day in the open. In the Hazaribagh neighborhood of Dhaka in
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...
, 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 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 , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = "Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capit ...
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 was caught directly dumping waste water into a wetland adjacent to
Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
.


Role of enzymes

Enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s like
protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...
s,
lipase Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually tr ...
s, and
amylase An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ') into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of ...
s 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 Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
or
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
, but should hydrolyze
casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...
,
elastin Elastin is a protein that in humans is encoded by the ''ELN'' gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the bod ...
,
albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...
,
globulin The globulins are a family of globular proteins that have higher molecular weights than albumins and are insoluble in pure water but dissolve in dilute salt solutions. Some globulins are produced in the liver, while others are made by the immune ...
-like proteins, and nonstructural proteins that are not essential for leather making. This process 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.


Preservation and conditioning

The natural fibers of leather break down with the passage of time. Acidic leathers are particularly vulnerable to
red rot Red rot is a degradation process found in vegetable-tanned leather. Red rot is caused by prolonged storage or exposure to high relative humidity, environmental pollution, and high temperature. In particular, red rot occurs at pH values of 4.2 ...
, which causes powdering of 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 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 a wet cloth or soaking the leather in water. Various treatments are available such as
conditioners A conditioner is something that betterment, improves the quality of another material. Conditioner may more specifically refer to: * Conditioner (chemistry) * Conditioner (farming) * Air conditioner * Fabric conditioner * Hair conditioner * Leathe ...
.
Saddle soap Saddle soap is a compound used for cleaning, conditioning, and protecting leather. It typically contains mild soap, softening ingredients such as lanolin, and preservatives such as beeswax. It is commonly used on leather footwear, saddles, and ot ...
is used for cleaning, conditioning, and softening leather. Leather shoes are widely conditioned with
shoe polish Shoe polish (or boot polish) is a waxy paste, cream, or liquid that is used to polish, shine, and waterproof leather shoes or boots to extend the footwear's life and restore its appearance. Shoe polishes are distinguished by their textures, ...
.


In modern culture

Due to its excellent resistance to abrasion and wind, leather found a use in rugged occupations. The enduring image of a
cowboy A cowboy is an animal herder who tends cattle on ranches in North America, traditionally on horseback, and often performs a multitude of other ranch-related tasks. The historic American cowboy of the late 19th century arose from the '' vaquer ...
in leather
chaps Chaps ( or ) are sturdy coverings for the legs consisting of leggings and a belt. They are buckled on over trousers with the chaps' integrated belt, but unlike trousers, they have no seat (the term "assless chaps" is a tautology) and are not jo ...
gave way to the leather-jacketed and leather-helmeted
aviator An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...
. When
motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...
s were invented, some riders took to wearing heavy leather
jackets A jacket is a garment for the upper body, usually extending below the hips. A jacket typically has sleeves, and fastens in the front or slightly on the side. A jacket is generally lighter, tighter-fitting, and less insulating than a coat, which ...
to protect from
road rash Road rash is a colloquial term for skin injury caused by abrasion with road surfaces, often as a consequence of cycling and motorcycling accidents. It may also result from running, inline skating, roller skating, skateboarding, and longboarding ...
and wind blast; some also wear chaps or full leather pants to protect 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 glove A baseball glove or mitt is a large glove (traditionally made of leather, today other options do exist) worn by baseball players of the defending team, which assists players in catching and fielding balls hit by a batter or thrown by a teammate ...
s and the ball used in
cricket Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by striki ...
and
gridiron football Gridiron football,"Gridiron football"
''Encyclopædia Britannica''. Ret ...
.
Leather fetishism Leather subculture denotes practices and styles of dress organized around sexual activities that involve leather garments, such as leather jackets, vests, boots, chaps, harnesses, or other items. Wearing leather garments is one way that parti ...
is the name popularly used to describe a
fetishistic A fetish (derived from the French , which comes from the Portuguese , and this in turn from Latin , 'artificial' and , 'to make') is an object believed to have supernatural powers, or in particular, a human-made object that has power over oth ...
attraction to people wearing leather, or in certain cases, to the garments themselves. Many
rock group A musical ensemble, also known as a music group or musical group, is a group of people who perform instrumental and/or vocal music, with the ensemble typically known by a distinct name. Some music ensembles consist solely of instrumentalists, ...
s (particularly heavy metal and
punk Punk or punks may refer to: Genres, subculture, and related aspects * Punk rock, a music genre originating in the 1970s associated with various subgenres * Punk subculture, a subculture associated with punk rock, or aspects of the subculture s ...
groups in the 1970s and 80s) are well known for wearing leather clothing.
Extreme metal Extreme metal is a loosely defined umbrella term for a number of related heavy metal music subgenres that have developed since the early 1980s. It has been defined as a "cluster of metal subgenres characterized by sonic, verbal, and visual tran ...
bands (especially
black metal Black metal is an extreme metal, extreme subgenre of heavy metal music. Common traits include Tempo#Beats per minute, fast tempos, a Screaming (music)#Black metal, shrieking vocal style, heavily distorted Electric guitar, guitars played with t ...
bands) and
Goth rock Gothic rock (also called goth rock or simply goth) is a style of rock music that emerged from post-punk in the United Kingdom in the late 1970s. The first post-punk bands which shifted toward dark music with gothic overtones include Siouxsie an ...
groups have extensive
black leather Fetish fashion is any style or appearance in the form of a type of clothing or accessory, created to be extreme or provocative in a fetishistic manner. These styles are by definition not worn by the majority of people; if everyone wears an it ...
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.


Religious sensitivities

In countries with significant populations of individuals observing religions which place restrictions on material choices, vendors typically clarify the source of leather in their products. Such labeling helps facilitate religious observance, so, for example, a
Muslim Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...
will not accidentally purchase pigskin or a
Hindu Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
can avoid cattleskin. Such
taboo A taboo or tabu is a social group's ban, prohibition, or avoidance of something (usually an utterance or behavior) based on the group's sense that it is excessively repulsive, sacred, or allowed only for certain persons.''Encyclopædia Britannica ...
s increase the demand for religiously neutral leathers such as
ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
and
deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindeer ...
.
Judaism Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in the ...
forbids the comfort of wearing leather shoes on
Yom Kippur Yom Kippur (; he, יוֹם כִּפּוּר, , , ) is the holiest day in Judaism and Samaritanism. It occurs annually on the 10th of Tishrei, the first month of the Hebrew calendar. Primarily centered on atonement and repentance, the day's ...
,
Tisha B'Av Tisha B'Av ( he, תִּשְׁעָה בְּאָב ''Tīšʿā Bəʾāv''; , ) is an annual fast day in Judaism, on which a number of disasters in Jewish history occurred, primarily the destruction of both Solomon's Temple by the Neo-Babylonian E ...
, and during mourning. Also, see
Teffilin Tefillin (; Israeli Hebrew: / ; Ashkenazic pronunciation: ), or phylacteries, are a set of small black leather boxes with leather straps containing scrolls of parchment inscribed with verses from the Torah. Tefillin are worn by adult Jews durin ...
and
Torah Scroll A ( he, סֵפֶר תּוֹרָה; "Book of Torah"; plural: ) or Torah scroll is a handwritten copy of the Torah, meaning the five books of Moses (the first books of the Hebrew Bible). The Torah scroll is mainly used in the ritual of Tora ...
.
Jainism Jainism ( ), also known as Jain Dharma, is an Indian religions, Indian religion. Jainism traces its spiritual ideas and history through the succession of twenty-four tirthankaras (supreme preachers of ''Dharma''), with the first in the current ...
prohibits the use of leather, since it is obtained by killing animals.


Alternatives

Many forms of
artificial leather Artificial leather, also called synthetic leather, is a material intended to substitute for leather in upholstery, clothing, footwear, and other uses where a leather-like finish is desired but the actual material is cost prohibitive or unsuitab ...
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 Naugahyde is an American brand of artificial leather. Naugahyde is a composite knit fabric backing and expanded polyvinyl chloride (PVC) coating. It was developed by Byron A. Hunter, senior chemist at the United States Rubber Company, and is now ...
. Another alternative is cultured leather which is lab-grown using cell-culture methods, mushroom-based materials and gelatin-based textile made by
upcycling Upcycling, also known as creative reuse, is the process of transforming by-products, waste materials, useless, or unwanted products into new materials or products perceived to be of greater quality, such as artistic value or environmental value ...
meat industry waste. Leather made of
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
or mushroom-based materials are completely biodegradable.


References


Further reading

* * * * * (includes several diagrams) {{Authority control Hides (skin)