Leather
Leather making has been practiced for more than 7,000 years. Ancient civilizations developed methods to transform raw animal hides into durable materials that could last for decades. The oldest known method involves tannins extracted from vegetable matter like tree bark prepared in bark mills. This process creates a supple material that is light brown in color. The exact shade depends on the mix of materials and the color of the skin. Historically, boiled leather was occasionally used as armor after hardening. It also found use for book binding. Tanning stabilizes proteins particularly collagen within the raw hide to increase thermal chemical and microbiological stability. Raw hides dry out to form a hard inflexible material that will putrefy when rewetted. Tanned material dries to a flexible form that does not become putrid when rewetted. Leading producers of leather today are China and India. These nations continue ancient traditions while adapting them to modern industrial scales.
The leather manufacturing process divides into three fundamental subprocesses: preparatory stages, tanning, and crusting. A further subprocess called finishing can be added but not all leathers receive it. Preparatory stages include soaking hair removal liming deliming bating bleaching and pickling. Tanners load hides into a drum and immerse them in a tank containing tanning liquor. The hides soak while the drum slowly rotates about its axis. The tanning liquor penetrates through the full thickness of the hide once even penetration is achieved workers raise the liquor's pH in a process called basification. This fixes the tanning material to the leather. Crusting thins and lubricates leather often including a coloring operation. Chemicals added during crusting must be fixed in place. Crusting culminates with drying and softening operations which 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 water resistance using mink oil neatsfoot oil or similar materials.
Most leather comes from cattle hides which constitute about 65% of all leather produced. Other animals used include sheep at about 13% goats at about 11% and pigs at about 10%. Horse hides make particularly durable leather. Shell cordovan is a horse leather made not from the outer skin but from an under layer found only in equine species. 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 reflect the scales of their species. The Argentine black and white tegu is one of the most exploited reptile species in the world in the leather trade. Kangaroo leather makes 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. Ostrich leather has a characteristic goose bump look because of large follicles where feathers grew. In Thailand stingray leather is used in wallets and belts. Stingray leather is tough and durable often dyed black and covered with tiny round bumps. For a given thickness fish leather is typically much stronger due to criss-crossed fibers.
Leather produces environmental impact notably due to carbon footprint of cattle rearing and use of chemicals in tanning processes. Estimates of the carbon footprint of bovine leather range from 65 to 150 kg of CO2 equivalent per square meter of production. 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 reach 200, 800 mg/L with high levels of fat and other solid wastes. Producers often add pesticides to protect hides during transport. With solid wastes representing up to 70% of wet weight of original hides the process strains water treatment installations. Tanning is especially polluting in countries where regulations are lax such as India the world's third-largest producer. In Kanpur self-proclaimed Leather City of World with 10,000 tanneries as of 2011 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 main tanneries' effluent disposal unit was dumping 22 tonnes of chromium-laden solid waste per day in open. In Hazaribagh neighborhood of Dhaka in Bangladesh chemicals from tanneries end up in Dhaka's main river.
Leather found use in rugged occupations due to its high resistance to abrasion and wind. The enduring image of a cowboy in leather chaps gave way to leather-jacketed and leather-helmeted aviators. When motorcycles were invented some riders took to wearing heavy leather jackets to protect from road rash and wind blast. Many sports use equipment made with leather such as baseball gloves and ball used in cricket and gridiron football. Leather fetishism describes attraction to people wearing leather or garments themselves. Many rock groups particularly heavy metal and punk groups in 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 punk community over last three decades as there is opposition to use of leather from punks who support animal rights. Many cars and trucks come with optional or standard leather or leather faced seating. Patent leather dating to late 1700s became widely popular after inventor Seth Boyden developed first mass-production process using linseed-oil-based lacquer in 1818.
In countries with significant populations observing religions which place restrictions on material choices vendors typically clarify source of leather in products. Such labeling helps facilitate religious observance so Muslim will not accidentally purchase pigskin or Hindu can avoid cattleskin. Such taboos increase demand for religiously neutral leathers such as ostrich and deer. Judaism forbids comfort of wearing leather shoes on Yom Kippur Tisha B'Av and during mourning. Jainism prohibits use of leather since it is obtained by killing animals. These dietary laws influence sourcing choices and consumer behavior across different faiths. Vendors must navigate complex requirements to ensure their products align with specific religious mandates. The market responds by offering alternatives that meet these ethical standards while maintaining durability and style. Religious sensitivities drive innovation in the industry as companies seek to serve diverse global markets without compromising core values.
Many forms of artificial leather have been developed usually involving polyurethane or vinyl coatings applied to cloth backing. Many names and brands exist including pleather portmanteau of plastic leather and brand name Naugahyde. Another alternative is cultured leather 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. Vinyl and petrochemical-derived materials take 500 or more years to decompose compared to leather which takes 25 to 40 years to break down. Enzymes like proteases lipases and amylases play important role in soaking dehairing degreasing and bating operations. Proteases most commonly used enzyme hydrolyze casein elastin albumin globulin-like proteins and nonstructural proteins not essential for leather making. Lipases used in degreasing operation to hydrolyze fat particles embedded in skin. Amylases soften skin bring out grain impart strength and flexibility though rarely used. These biological tools offer potential for reducing chemical reliance while maintaining material integrity.
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Common questions
When did leather making start and what was the oldest method used?
Leather making has been practiced for more than 7,000 years. The oldest known method involves tannins extracted from vegetable matter like tree bark prepared in bark mills.
Which countries are leading producers of leather today and how many tanneries were in Kanpur as of 2011?
Leading producers of leather today are China and India. Kanpur had 10,000 tanneries as of 2011.
What percentage of all leather produced comes from cattle hides and which animal provides shell cordovan?
Most leather comes from cattle hides which constitute about 65% of all leather produced. Shell cordovan is a horse leather made not from the outer skin but from an under layer found only in equine species.
How much carbon footprint does bovine leather produce per square meter and when were high-polluting tanneries shut down in Kanpur?
Estimates of the carbon footprint of bovine leather range from 65 to 150 kg of CO2 equivalent per square meter of production. The pollution control board decided to shut down 49 high-polluting tanneries out of 404 in July 2009.
Who invented the first mass-production process for patent leather and what year was it developed?
Patent leather dating to late 1700s became widely popular after inventor Seth Boyden developed first mass-production process using linseed-oil-based lacquer in 1818.