The modern commercial leather-making process involves three basic phase
The term hide is used to designate 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 process employed is a chemical treatment called tanning, which converts the otherwise perishable skin to a stable and nondecaying material. Although the skins of such diverse animals as ostrich, lizard, eel, and kangaroo have been used, the more common leathers come from seven main groups: cattle, including calf and ox; sheep and lamb; goat and kid; equine animals, including horse, mule, and zebra; buffalo; pig and hog; and such aquatic animals as seal, walrus, whale, and alligator.
The hides of mammals are composed of three layers: epidermis, a thin outer layer; corium, or dermis, the thick central layer; and a subcutaneous fatty layer. The corium is used to make leather after the two sandwiching layers have been removed. Fresh hides contain between 60 and 70 percent water by weight and 30 to 35 percent protein. About 85 percent of the protein is collagen, a fibrous protein held together by chemical bonds. Basically, leather making is the science of using acids, bases, salts, enzymes, and tannins to dissolve fats and nonfibrous proteins and strengthen the bonds between the collagen fibres.
Leather making is an ancient art that has been practiced for more than 7,000 years. Primitive man dried fresh skins in the sun, softened them by pounding in animal fats and brains, and preserved them by salting and smoking. Beginning with simple drying and curing techniques, the process of vegetable tanning was developed by the Egyptians and Hebrews about 400 BC. During the Middle Ages the Arabs preserved the art of leather making and so improved it that morocco and cordovan (from Córdoba, Spain) became highly prized leathers. By the 15th century, leather tanning was once more widespread in Europe, and, by the mid-19th century, power-driven machines that performed such operations as splitting, fleshing, and dehairing were introduced. Toward the end of the 19th century, chemical tannage—in particular, the use of chrome salts—was introduced.
The modern commercial leather-making process involves three basic phases: preparation for tanning, tanning, and processing tanned leather. As a preliminary step, a hide must be carefully skinned and protected both in storage and transportation before reaching the china leather factory. A hide will begin to decompose within hours of an animal’s death; to prevent this from happening, the hide is cured by a dehydrating process that involves either air-drying, wet or dry salting, or pickling with acids and salts before being shipped to a tannery.