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Leather is a material of animal origin with its original fibrous structure more or less intact, tanned to be imputrescible, where the hair or wool may or may not have been removed, whether or not the hide or skin has been split into layers either before or after tanning and where any surface coating or surface layer, however applied, is not thicker than 0,15 mm.[1]
[CAN'T EDIT NEW INTRO - PLEASE COPY WORDING FROM LEATHERMASTER]
A variety of leather products and leather-working tools
OLD INTRO:
Leather is a flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay.[2] The most common raw material used in leather production is cattle hide, which constitutes approximately 69% of all leather.
Leather is used to make a variety of products, including clothing, footwear, accessories, furniture, tools and sports equipment, due to its [PROPERTIES]. Leather making has been practiced for more than 7,000 years [MORE ABOUT HISTORY][3]. The leather industry (including manufacture of products and trade of raw hides) exceeds $80 billion annually,[4] resulting in China and India being the largest producers of leather today.[2][5]
The ethics of leather production are controversial with animal rights groups claiming that modern commercial leather making and the consumption of its products is unethically killing animals.[6] However, according to the 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.[7] Sustainability is also a topical issue in the leather industry relating to the carbon footprint of cattle rearing, chemical management, air pollution and water usage involved in the leather making process. [REF?]
International Trade (currently 208 words max 400) (submitted for all to review)
The worldwide leather industry produces approximately 23-24 billion square feet of leather per year.[8] The value of international trade of raw hides and skins (other than furskin) and leather is nearly $20 billion, and it is the 75th most traded commodity in the world.[9] When combined with leather products (such as footwear, garments and accessories), international trade exceeds $80 billion annually[4] (excluding leather and fashion furs derived from wild and exotic animals, which are banned from international trade by CITES).[4]
Top 5 Raw Hides and Skins and Leather Importing and Exporting Countries
The global leather goods market including leather footwear is valued at $407.92 billion and according to CAGR analysis will grow by 5.9% reaching $624.08 billion in 2028.[11] In developing countries, leather and leather goods production is a labour intensive industry that provides employment to the lower social class often in rural areas.[12] Only in India, 4.42 million people find employment in leather industries with 30% being women .[12] In developed countries due to processes automatisation and optimisation less workforce is required. In the EU, where around 12% of world leather is produced,[10] the leather industries generate a turnover of EUR 48 billion and employ 435,000 people in 36,000 enterprises.[13]
Today, 99% of leather is produced from 4 types of livestock; bovine (69%), sheep (13%), goat (11%) and pig (6%). The remaining 1% is sourced from other animals such as exotics and fish.[14]
Bovine (69%): <Insert brief description> The value of premium US steer hides, the most valuable leather raw material, represent approximately 2.2% of the total market value of the animal. [15] In the US, nearly 14.5% of all cattle hides produced go to landfill, due to low demand [16] <WEAK REF>. Globally, it is estimated that X% of hides end up landfilled or incinerated (ref).
Other animals (1%): Equine and kangaroo hides are used to make particularly durable leathers due to their natural strength. <REF> In contrast, deer skin is used for soft leather. <REF> Reptile (such as alligator, crocodile and snake) and stingray skins are noted for their distinct patterns that reflect the scales of their species, these are often highlighted during the finishing process. <REF> Similarly, Ostrich skin has a characteristic "goosebump" look because of the large follicles where the feathers grew. <REF> Fish leather, given its thickness, is typically much stronger due to its criss-crossed fibers. [17]
Production Processes (currently 358 word max 600) (Norbert drafting)
The leather manufacturing process is divided into three fundamental sub-processes: preparatory stages, tanning, and crusting. There is also a fourth optional sub-process known as finishing. [DIAGRAM?] [REF]
The preparatory stages are when the hide is prepared for tanning. Preparatory stages may include soaking, hair removal, liming, deliming, bating, bleaching, and pickling. [REF]
Leather manufacturing flowchartTanning 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 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. [REF] 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. [REF]
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, whitening or other methods. [REF]
The optional stage of finishing involves tanners applying a surface coating. Finishing operations can include oiling, brushing, buffing, coating, polishing, embossing, glazing, or tumbling, among others. [REF]
[WHERE DOES THIS GO?] Leather can be oiled to improve its water resistance. This currying 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, neatsfoot oil, or a similar material keeps it supple and improves its lifespan dramatically.[18]
Role of Enzymes (currently 104 words 200 max) (Rachel drafting)
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 is called bating.[19]
Lipases are used in the degreasing operation to hydrolyze fat particles embedded in the skin.[20]
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.
Tanning processes largely differ in which chemicals are used in the tanning liquor. Some common types include:
Vegetable-tanned leather [ALSO KNOWN AS VEGETAN?] is tanned using tannins extracted from vegetable matter, such as tree bark prepared in bark mills. It is the oldest known method. [SENTENCE TOO SHORT] 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 tends to discolor in water, and if left to soak and 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 is an example of this, where the leather has been hardened by being immersed in hot water, or in boiled wax or similar substances. Historically, it was occasionally used as armor after hardening, and it has also been used for book binding.[21][22]
Chrome-tanned leather is tanned using chromium sulfate and other chromiumsalts. It is also known as "wet blue" due to the pale blue color of the undyed leather. The chrome tanning method takes approximately one day to complete, making it best suited for large-scale industrial use. This is the most common method in modern use. [TOO SHORT] It is more supple and pliable than vegetable-tanned leather and does not discolor or lose shape as drastically in water compared to 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 explored methods to speed up the process and make leather more waterproof.[23][22] [MENTION REGULATIONS?]
Aldehyde-tanned leather is tanned using glutaraldehyde or oxazolidine compounds. It is referred to as "wet white" due to its pale cream color. It is the main type of "chrome-free" leather, often used in shoes for infants and automobiles. Formaldehyde 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. [MENTION REGULATION?]
Chamois leather is a form of aldehyde tanning that produces a porous and highly water-absorbent leather. Chamois leather is made using marine oils (traditionally cod oil) that oxidize to produce the aldehydes that tan the leather.
Brain-tanned leather is 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 salts mixed with a variety of binders and protein 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 aluminium salts.
Leather Classifications (397 words max 500) (unassigned)
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 during its useful lifetime. Considered the highest quality of leather, it is frequently used for furniture and footwear. Full-grain leather is typically finished with a soluble aniline dye. Russia leather is a form of full-grain leather.
Corrected-grain leather has the surface [CHANGE TO IS?] 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 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 remaining corium 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 is split leather that has a polyurethane or vinyl layer applied to the surface and embossed to give it the appearance of a grain. It is slightly stiffer than top-grain leather but has a more consistent texture.
Patent leather 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 developed the first mass-production process, using a linseed-oil-based lacquer, in 1818. Modern versions are usually a form of bicast leather.
Suede 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. [WHAT DOES THIS MEAN?]
Bonded leather, also called reconstituted leather, is a material that uses leather scraps that are shredded and bonded together with polyurethane or latex onto a fiber mesh. The amount of leather fibers in the mix varies from 10% to 90%, affecting the properties of the product.[24]
The process of leather making has been practiced for more than 7,000 years.[25] In the prehistoric period, Homo sapiens would use animal hides for protection in cold climates to provide warmth. [26] However, the raw hides and skins would eventually putrefy or dry out making them rigid, stiff and inflexible, therefore different civilisations started to apply various techniques to cure and treat the hides and skins to strengthen and preserve them. <REF> The early tanning process involved drying fresh skins in the sun which were softened by animal fats and brains, further preserved by salting and smoking.[25]
Several artefacts have been discovered evidencing the process of leather making throughout history:
Evidence of the oldest surviving leather shoe known as the Areni-1 shoe was discovered in 2010 in the Areni-1 cave in the Vayotz Dzor Province of Armenia. [27] Estimated at 5,500 years old (dating back to 3,500 BCE), archeologists believe the shoe’s preserved state was due to the stable, cool and dry conditions within the cave as well as the floor of the cave being covered by a thick layer of sheep dung which acted as a preservative seal. [27]
The oldest leather manuscript dates back to 2,300 BC - 2,000 BC during the Ancient Egyptian period. [29]
The grave of Tutankhamun (buried 1500 BC) contained sandals made of wood and overlaid with a marquetry veneer of bark, green leather and gold foil on a stucco base. [30]
Tanning techniques and the applications of leather continued to develop during Ancient History, into the Middle Ages. By Medieval times, leather was already a mass-produced material used to make footwear, garments, gloves, bags and accessories, as well as being used in bookbinding, upholstery and saddlery <REF>. Vegetable tanning techniques were developed by the Moors, an indigenous culture that arrived in mainland Europe in the 8th century <REF>. Clusters of leather producers shortly began to appear in Italy (Tuscany and Florence), Spain (Córdoba), Morocco (Fez), Germany (Nuremberg), Turkey (Anatolia) and the UK (Northampton). <REF> Due to the increased prominence of tanning in Europe, the Tanner's Guild was formed in the 11th century to aid and protect the trade and is believed to be one of the oldest guilds in Europe. [31]
The Industrial Revolution lead to substantial changes in the leather making process. The introduction of machinery, which itself used leather for drive belts, reduced the lead time for leather production. <REF> By the mid-19th century, power-driven machines performed operations such as splitting, fleshing, and dehairing. [32] This resulted in almost 16% of the workforce in America being employed in leather-related trades in the 1850s. <REF>
Leather working in Nuremberg, Germany depicted in Conrad Mendel manuscript "House Book of Mendel" dated 1425.
In 1858, Friedrich Ludwig Knapp patented and introduced chromium (chrome) tanning, a faster and cheaper method of tanning that over time, has reduced the popularity of the traditional process of vegetable tanning. <REF> Currently chrome tanning accounts for approximately 85% of the world's leather. <REF>
Leather dominated the markets and was one of the most traded materials until the 1960s. <REF> However, the technological advancements during WWI and WWII led to new materials being developed such as plastics and rubbers, which led to a decline in demand for genuine leather. <REF>
The globalisation process provoked the shift of leather production to developing countries, where producers benefit from low wages, reduced socio-environmental regulations and cheaper raw materials. <REF> These changes have resulted in due diligence and environmental issues. <MORE INFO/REF>
The natural fibers of leather break down with the passage of time. Acidic leathers are particularly vulnerable to red rot, 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.
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.[33]
Tanneries are B2B companies that supply leather (by volume) to footwear (47%), automotive (17%), leather goods (12%), furniture (10%), apparel (10%) and gloves (4%) industries4. In 2019 leather was used to produce 3 billion pairs of shoes, 19 million vehicles with leather interior, $70 billion worth of leather goods, garment and gloves, and $31 billion of leather furniture.
Due to its resistance to abrasion and wind, leather is frequently used in rugged occupations [REF]. 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 the lower body. [REF] [WORKWEAR?]
Leather's flexibility also allows it to be formed and shaped into balls and protective gear. Subsequently, many types of sports equipment are made from leather, such as baseball gloves and the ball used in American football. [MORE EXAMPLES] [REF]
Leather fetishism is the name popularly used to describe a fetishistic attraction to people wearing leather, or in certain cases, to the garments themselves.
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 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.
Critics of tanneries claim that they engage in unsustainable practices that pose health hazards to the people and the environment near them.[35] [SOME] 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.[36]
Leather produces some environmental impact, most notably due to: [SHOULD LIST ALL BELOW]
Air pollution due to the transformation process (hydrogen sulfide is formed during mixing with acids and ammonia liberated during deliming, solvent vapors)
Worldwide 40% of hides are disposed of (USHSLA,2021). In the US, in 2019, almost 16% of cattle hides (4.8mln) were discarded (Kay, 2020) that could have instead been used to produce leather for approximately 86.4 million pairs of shoes (USLHCA, 2021), which are now more often produced using synthetic materials instead - leather international footwear export dropped from 75% to 40% (value-wise) and from 33% to 15% (volume-wise) from early 2000 to 2016 with the clear upward trend in rubber and plastic footwear (APICCAPS, 2011). At the same time, FAO (2013) reports that cow farming is responsible for 14.5% of GHG emissions, but it remains undetermined how much of that carbon footprint should be borne with meat, dairy products and leather. Fair and transparent allocation of carbon footprint between the economic actors is not possible without the understanding of upstream supply chains, therefore more studies are needed to determine if and how much better off the world is if we make use of all the hides available. <FOR REVISION>
Estimates of the carbon footprint of bovine leather range from 65 to 150 kg of CO2 equivalent per square meter of production.[37]
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.[38]
OLD ARTICLE:Leather biodegrades slowly—taking 25 to 40 years to decompose.[39][failed verification] However, vinyl and petrochemical-derived materials take 500 or more years to decompose.[40]
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 a properly managed facility. A review of the total pollution load decrease achievable according to the United Nations Industrial Development Organization[41] 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, 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.[42] In 2003 for instance, the main tanneries' effluent disposal unit was dumping 22 tonnes of chromium-laden solid waste per day in the open.[43]
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.[44] 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.[45]
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.[46] In November 2009, one of Uganda's main leather making companies was caught directly dumping waste water into a wetland adjacent to Lake Victoria.[47]
Sector growth has slowed due to leather being replaced with competitive, synthetic materials. As a result, the share of leather shoes in international footwear export dropped from 75% to 40% (value) and from 33% to 15% (volume) between 2000-2016 with the clear upward trend in rubber and plastic footwear11.
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.[48]
Another alternative is cultured leather which is lab-grown using cell culture methods,[49][50] mushroom-based materials and gelatin-based textile made by upcycling meat industry waste.[51][52]
^Chen et. al., Analyzing the Carbon Footprint of the Finished Bovine Leather: A Case Study of Aniline Leather Energy Precidia 61, 2014, p. 1063. https://doi.org/10.1016/j.egypro.2014.11.1023
^"The scope for decreasing pollution load in leather processing"(PDF). United Nations Industrial Development Organization Regional Programme for Pollution Control in the Tanning Industry in South-East Asia. 9 August 2000. Archived from the original(PDF) on November 2017. Retrieved 2 January 2010. {{cite web}}: Check date values in: |archive-date= (help)
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