What is Leather... animal skins and hides that have been treated with chemicals to preserve them and make them suitable for use as clothing, footwear, handbags, furniture, tools, and sports equipment.
The term hide is used to designate the skin of larger animals, for example cow or horse, whereas skin refers to that of smaller animals such as calf or sheep.
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tan (v.) late Old English tannian "to convert hide into leather" (by steeping it in tannin), from Medieval Latin tannare "tan, dye a tawny color" (c. 900), from tannum "crushed oak bark," used in tanning leather, probably from a Celtic source (such as Breton tann "oak tree"). The meaning "make brown by exposure to the sun" (as tanning does to hides) first recorded 1520s; intransitive sense also from 1520s. Of persons, not considered an attractive feature until 20c.; in Shakespeare, "to deprive of the freshness and beauty of youth" (Sonnet CXV). As an adjective from 1620s. To tan (someone's) hide in the figurative sense is from 1660s. Related: Tanned; tanning. German Tanne "fir tree" (as in Tannenbaum) might be a transferred meaning from the same Celtic source.
Tannin is a yellowish or brownish bitter-tasting organic substance present in some galls, barks, and other plant tissues, consisting of derivatives of gallic acid. It is this that is used in the "Vegetable Tanning" process
The preservation process employed is a chemical treatment called tanning, which converts the otherwise perishable skin to a stable and non-decaying material.
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Tanning agents include vegetable tannin (from sources such as tree bark), mineral salts (such as chromium sulphate), and fish or animal oils.
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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 tannin to dissolve fats and non-fibrous proteins and strengthen the bonds between the collagen fibres.