Leather, hides and animal skins is a durable and flexible materials treated with chemicals to preserve them and make them suitable for use as clothing, footwear, handbags, furniture, tools, and sports equipment. The most common raw material is cattle hide. It can be produced at manufacturing scales ranging from artisan to modern industrial scale.

The word hide is used to refer to the skin of larger animals (e.g., cowhide or horsehide), whereas skin refers to that of smaller animals (e.g., calfskin or kidskin). The preservation method is a chemical procedure called tanning, which converts skin that is otherwise perishable into a stable and non-decaying material. Tanning agents include tannins from vegetables (such as tree bark), mineral salts (such as chromium sulfate) and fish or animal oils. Although the skins of animals such as ostriches, lizards, eels, fish and kangaroos have been used, the more traditional leathers come from seven main groups: cows, including calves and oxen; sheep and lambs; goats and children; horses, mules and zebras; buffalo; pigs and hogs; and aquatic animals such as seals, walrus, whales, and alligators.

There are three types of mammalian hides: epidermis, a thin outer layer; corium, or dermis, a dense central layer; and a subcutaneous fatty layer. The corium is used to make leather after the removal of the two sandwiched layers. New hides contain water by weight between 60 and 70% and protein between 30 and 35%. Collagen is about 85% of the protein, a fibrous protein that is kept together by chemical bonds. Leather making is simply the process of using acids, bases, salts, enzymes, and tannins to dissolve fats and non-fibrous proteins and reinforce the bonds between the collagen fibers.

The vegetable tanning method was developed by the Egyptians and Hebrews around 400 BCE, beginning with basic drying and healing techniques. The Arabs maintained the art of leather making during the Middle Ages and developed it in such a way that Morocco and Córdoba (from Córdoba, Spain) became highly prized leathers. By the 15th century, leather tanning was once again popular in Europe and power-driven machines were introduced in the mid-19th century that performed such operations as splitting, fleshing and dehairing. Chemical tannage — including the use of oak, sumac, and hemlock tanbark and chrome salts — was introduced towards the end of the 19th century.

Due to its toughness and comfort, leather has been utilized for seating since the commencement of transportation and furniture. It has consistently been the perfect material for making seats and tack, just as footwear. During the Middle Ages, leather became the cover of choice for dining chairs, because it was easy to maintain and did not absorb the odor of food.

West Bengal has a long history of leather production. It’s leather products made in thousands of big and small scale units have occupied a position of prestige for many years. The state is a pioneer in the manufacture and export of artistic leather goods, shoes, and sports goods. Calcutta has been the premier chrome tanning center in the country for several decades.

Though the tanning industry in Calcutta made its beginning in the present century, Calcutta had become an important port for leather export long ago. Leather trade with Europe and America had been definitely established in Calcutta by the 1820s. The quality of cow-hides, calfskins, goat skins, and reptile-skins of Bengal acquired a big reputation not only in India but also in Europe and America.

Current innovation has taken into account advancement in the cowhide business, as the improvement of synthetic concoctions and modern preparing techniques have enormously extended the style and feel of leather just as the potential applications. The leather keeps on being the material of decision, for business and private furniture as well as for the car, avionics, and marine applications also.

The modern commercial method of leather making includes three basic phases: tanning preparation, tanning, and storage of tanned leather. Until entering the tannery, a hide must be skinned carefully and covered in storage and transportation. A hide will start to decompose within hours of the death of an animal; to avoid this, a dehydration process that involves either air-drying, wet or dry salting, or pickling with acids and salts before shipment to a tannery will cure the hide.

The hide is soaked at the tannery to extract and restore all water-soluble materials to its original shape and softness. Hair is typically loosened by a process called liming, which is achieved by immersing the hides in a mixture of lime and water; the hair and the flesh and tissue are extracted by machine. The hide is then cleaned, processed, bated (the enzymatic extraction of non-fibrous protein to improve color and softness) and pickled (to provide final purification and softening).

The tanning method derives its name from tannin (tannic acid), the agent that displaces water from the interstices of the protein fibers of the hide and binds together these fibers. Vegetable tanning is still important, which is the oldest type of tanning. Extracts are taken from the high tannin-rich parts of plants (such as roots, bark, leaves, and seed husks). The material extracted is refined into tanning liquors and the hides are soaked in increasingly strong liquor vats or drums until they are tanned enough. It can take weeks or months to complete the different vegetable tanning procedures. The end result is a durable leather that is water-resistant.

Mineral tanning, which uses mineral salts, provides a soft, smooth leather and is the preferred method to manufacture most light leathers. Chromium salt is the mineral agent most widely used, but it also contains aluminum and zirconium salts. The hides are immersed in saline baths with increased strength in mineral tanning or in acidic baths where chemical reactions accumulate salts in the skin fibers.

Oil tanning is an old method of processing or grinding fish oil or other oil and fatty substances onto dried hide until the natural moisture of the original skin has been removed. Oil tanning is mainly used to make chamois leather, smooth, flexible leather that can be wetted and dried repeatedly without injury. A wide variety of phenols and hydrocarbons based artificial tanning agents (or syntans) are also used. The pelts are ready for processing after the basic tanning process is completed, the final stage in the manufacture of leather. Next, the tanned pelt is thoroughly dried and then dyed to give it the right color; common methods include drum dyeing, spraying, brush dyeing and staining. Blended oils and greases are then mixed into the leather to lubricate it and improve its water-shedding softness, strength, and ability.

The leather is then dried up to approximately 14 percent humidity, either in the sun or in a drying tunnel or by stretching the leather first and then drying it with air or tunnel. Paste and vacuum drying are other approaches that are less commonly used. Reconditioning with humid sawdust to a standard moisture content of 20 percent finishes the dried leather. The grain surface is then extended and hardened to provide additional resistance to abrasion, cracking, peeling, moisture, heat, and cold.

The leather is then ready to be fashioned into any of a multitude of products. These include shoes and boots, outer apparel, belts, upholstery materials, suede products, saddles, gloves, luggage and purses, and recreational equipment as well as such industrial items as buffing wheels and machine belts.

In the 19th century, some of the first leather substitutes were invented. In 1845 German chemist Christian Friedrich Schönbein invented nitrocellulose (guncotton) and in 1846 French scientist Louis-Nicolas Ménard transformed it into a collodion (pyroxylin). Collodion was used in wound dressings as a protective coating, and was later applied to fabrics. Fabrikoid was a pyroxylin-infused cotton fabric, developed in 1910 and patented by the DuPont Fabrikoid company in 1915. It avoided rain and was widely used in items such as upholstery, book covers, linings, and coverings for vehicles. Naugahyde was first used in women’s handbags in the early 1920s, a material lined with leather fibers and rubber, before spreading into other industries. Since the 1960s, the popular styles of synthetic leather have been fabrics coated or sprayed with polyurethane and polyvinyl chloride, providing both the look and the strength of real leather.

Colloquially known as fake leather, imitation leather, and pleather, artificial leather has been seen as having many advantages over real leather. It can approximate the quality and durability of real leather at a lower cost, and is much less labor-intensive in its processing. Furthermore, the leather-making industry has been criticized by animal rights groups for its killing and abuse of animals. The mix of practical and ethical considerations has propelled the market for handbags, boots, clothes, and other fashion items for synthetic leather substitutes. The synthetic leather market’s volume was measured at over $50 billion by 2015.