Leather is a material created through the tanning of hides and skins of animals, primarily cattlehide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural material for various uses.
Together with wood, leather formed the basis of much ancient technology. The leather industry and the fur industry are distinct industries that are differentiated by the importance of their raw materials. In the leather industry the raw materials are by-products of the meat industry, with the meat having higher value than the skin. The fur industry uses raw materials that are higher in value than the meat and hence the meat is classified as a by-product. Taxidermy also makes use of the skin of animals, but generally the head and part of the back are used. Hides and skins are also used in the manufacture of glue and gelatin.
Leather—usually vegetable-tanned leather—can be oiled to improve its water resistance. This 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.
Leather with the hair still attached is called hair-on.
The International Union of Leather Technologists and Chemist Societies has a glossary of leather terms that can be found at IULTCS
Other less-common leathers include:
There are two other descriptions of leather commonly used in specialty products, such as briefcases, wallets, and luggage.
The following are not 'true' leathers, but contain leather material. Depending on jurisdiction, they may still be labeled as "Genuine Leather."
The vast majority of leather is sold according to its area. The leather is placed through pin-wheel or electronic measuring machines and its surface area is determined. The unit of measurement is square meter, square decimeter or square foot. The thickness is also important, and this is measured using a thickness gauge (the unit of measurement is millimeters, e.g., 1.8 mm is a standard thickness for a school shoe).
In some parts of the world, top-grain thicknesses are described using weight units of ounces. Although the statement is in ounces only, it is an abbreviation of ounces per square foot. The thickness value can be obtained by the conversion:
Hence, leather described as 7 to 8 oz is 7/64 to 8/64 inches (2.8 to 3.2 mm) thick. The weight is usually given as a range because the inherent variability of the material makes ensuring a precise thickness very difficult. Other leather manufacturers state the thickness directly in millimeters.
Today, most leather is made of cattle skin, but many exceptions exist. Lamb and deer skin are used for soft leather in more expensive apparels. Deer and elk skin are widely used in work gloves and indoor shoes. Pigskin is used in apparel and on seats of saddles.
Kangaroo skin is used to make items which need to be strong but flexible, it is the material most commonly used in high quality bullwhips. Kangaroo leather is favored by some motorcyclists for use in motorcycle leathers specifically because of its lighter weight and higher abrasion resistance compared with cowhide, thus providing greater protection in case of a fall on the roadway. Kangaroo leather is also used for high performance soccer footwear.
In the 1970s, ostrich farming for their feathers became popular, and ostrich leather became available as a side product. There are different processes to produce different finishes for many applications, i.e., upholstery, footwear, automotive products, accessories and clothing. Ostrich leather is considered one of the finest and most durable in the world and is currently used by many major fashion houses such as Hermès, Prada, Gucci, and Louis Vuitton. Ostrich leather has a characteristic "goose bump" look because of the large follicles from which the feathers grew.
In Thailand, sting ray leather is used in wallets and belts in the same way as regular bovine leather. Sting ray leather is as tough and durable as hard plastic. 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. Leather clothing is also popular in Thailand.
In the United States, bison leather has become popular. It is used for gloves, jackets and some baseball gloves. It is rugged but supple and has a waxy feel.
Overall, leather comes from a variety of other sources, including the skins of cattle, hogs, goats, sheep, alligators, ostriches, kangaroos, and yaks.
There is quite a wide range of different animal leather used both for leather garments as well as leather goods, such as handbags, wallets, purses, belts, bags and other customized leather articles.
The most commonly used leather types are cow leather, sheep leather, buffalo Leather and ox leather. Of these, the most expensive is cow leather, followed by buffalo leather, ox leather and sheep leather respectively. Sheep leather is quite famous for its softness and mostly used in leather garments; however due to its smaller overall size, it cannot be used for the long coats for which cow leather and buffalo leather are widely used.
The leather manufacturing process is divided into three fundamental sub-processes: preparatory stages, tanning and crusting. All true leathers will undergo these sub-processes. A further sub-process, surface coating can be added into the leather process sequence but not all leathers receive surface treatment. Since many types of leather exist, it is difficult to create a list of operations that all leathers must undergo.
The preparatory stages are when the hide/skin is prepared for tanning. Preparatory stages may include: preservation, soaking, liming, unhairing, fleshing, splitting, reliming, deliming, bating, degreasing, frizing, bleaching, pickling and depickling.
Tanning is the process which converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that when re-wetted (or wetted back) putrefy, while tanned material dries out to a flexible form that does not become putrid when wetted back. There is a large number of different tanning methods and materials that can be used, the choice is ultimately dependent on the end application of the leather. The most commonly used tanning material is chromium, which leaves the leather once tanned a pale blue color (due to the chromium), this product is commonly called “wet blue”. The hides once they have finished pickling will typically be between pH of 2.8-3.2. At this point the hides would be loaded in a drum and immersed in a float containing the tanning liquor. The hides are allowed to soak (while the drum slowly rotates about its axle) and the tanning liquor slowly penetrates through the full substance of the hide. Regular checks will be made to see the penetration by cutting the cross-section of a hide and observing the degree of penetration. Once a good even degree of penetration exists, the pH of the float is slowly raised in a process called basification. This basification process fixes the tanning material to the leather and the more tanning material fixed the higher the hydrothermal stability and increased shrinkage temperature resistance of the leather. The pH of the leather when chrome tanned would typically finish somewhere between 3.8-4.2.
Crusting is when the hide/skin is thinned, retanned and lubricated. Often, a coloring operation is included in the crusting sub-process. The chemicals added during crusting have to be fixed in place. The culmination of the crusting sub-process is the drying and softening operations. Crusting may include the following operations: wetting back, sammying, splitting, shaving, rechroming, neutralization, retanning, dyeing, fatliquoring, filling, stuffing, stripping, whitening, fixating, setting, drying, conditioning, milling, staking, and buffing.
For some leathers a surface coating is applied. Tanners refer to this as finishing. Finishing operations may include: oiling, brushing, padding, impregnation, buffing, spraying, roller coating, curtain coating, polishing, plating, embossing, ironing, ironing/combing (for hair-on), glazing and tumbling.
Proteases are the most commonly used enzymes in leather production. The enzyme used should not damage or dissolve collagen or keratin, but should be able to hydrolyze casein, elastin, albumin and globulin-like proteins, as well as non-structured proteins which are not essential for leather making. It is especially important to hydrolyze the elastin if the leather is to be limed, or treated with calcium hydroxide; if not treated properly before liming, the elastin will harden and the grain will be loose. 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.
The natural fibers of leather will 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, and is irreversible.
Exposure to long periods of low relative humidities (below 40%) can cause leather to become desiccated, irreversibly changing the fibrous structure of the leather.
Various treatments are available such as conditioners, but these are not recommended by conservators since they impregnate the structure of the leather artifact with active chemicals, are sticky, and attract stains.
Leather used in book binding has many of the same preservation needs: protection from high temperatures, high relative humidity, low relative humidity, fluctuations in relative humidity, light exposure, dust buildup, pollution, mold, and bug infestation.
For books with red rot, acid-free phase boxes and/or polyester dust jackets (Dupont Mylar Type D® or ICI Mellinex 516®) are recommended to protect the leather from further handling damage and as well as to prevent the residues from getting on hands, clothes, the text block, and nearby books.
The debate on the use of dressings for preservation of book bindings has spanned several decades as research and experimental evidence have slowly accumulated. The main argument is that, done incorrectly, there are multiple disadvantages and that, done correctly, there is little to no preservation advantage. Pamphlets and guidelines give numerous downsides to dressings use, including: the dressing becoming increasingly acidic, discolor and stain the leather, oxidize (penetration and expansion of oils including displacement and weakening of fibers) and stiffen, leave a sticky surface, collect dust, wick into adjacent materials, form unstable surface spews, encourage biological deterioration and mold growth, block surface porosity, impede further treatment, wet and swell the leather, affect surface finishes, and desiccate or dry out the leather.Meanwhile, scientific experiments have shown no great benefits.The main authorities on the subject therefore discourage it, with a caveat for special cases done under the direction of a conservator.
Cordwain, once a synonym to Cordovan (through Old French cordewan) meaning "from Córdoba". Painted or gilded embossed leather decoration for walls, a 12th century north African style, was introduced to Spain (hence it is sometimes referred to as 'Spanish leather'). Around the turn of the 15th-16th century the technique reached Flanders and Brabant in the Low Countries. Though there were craftsmen in several cities (such as Antwerp, Brussels, Ghent), the major handicraft center for this cordwain was Mechelen, where it was mentioned as early as 1504. Since the second half of the 18th century, this luxurious artisan product is no longer made. Cordwainer is still used to describe someone in the profession of shoemaking.
As leather can also be a metonymical term for objects made from it, the term leathering is as logical as tanning in the sense of a physical punishment (such as a severe spanking) applied with a leather whip, martinet, etc.
Leather fetishism is the name popularly used to describe a fetishistic attraction to people wearing leather, or in certain cases, to the garments themselves. The word leather itself became synonymous with sado-masochism in the 1980s after achieving that status in homosexual jargon in the 1970s.
Many rock groups (particularly heavy metal groups in the 1980s) are well-known for wearing leather clothing. Leather clothing, particularly jackets, almost come as standard in the heavy metal subculture. Extreme metal bands (especially black metal bands) and Goth rock groups have extensive leather clothing, i.e. leather pants, accessories, etc.
Many cars and trucks come with optional or standard 'leather' seating. This can range from cheap vinyl material, found on some low cost vehicles, to Nappa leather, found on luxury car brands like Mercedes-Benz, BMW, and Audi.
In Muslim countries, products made of leather were normally banned as due to the religious concerns imposed by some Islamic scholars, but in the mid-20th century, some eminent scholars from the Muslim world have made significant efforts to foster awareness about the origin of leather.
Some vegan and animal rights activists have boycotted use of all leather items, believing the practice of wearing animal hides is unnecessary and cruel in today's society. Animal rights groups such as PETA have issued pamphlets calling for boycotts and encouraging use of alternative materials such as synthetic leathers produced from petrochemicals.
Many pseudo-leather materials have been developed, allowing those who wish to wear leather-like garments to do so without actually wearing leather. One example of this is vegan microfiber, which claims to be stronger than leather when manufactured with strength in mind. Vinyl materials, pleather, Naugahyde, Durabuck, NuSuede, Hydrolite, and other alternatives exist, providing some features similar to leather.