Leather is made from animal skins. The first stage of the leather-making process involves stripping any remaining bits of flesh from the animal's hide, then removing all hairs from it. When this has been done, the core process of leather creation, known as tanning, can begin. Tanning involves treating the hide with a substance which will prevent it from rotting. Many different substances can be used to tan leather, and each tends to produce a slightly different effect on the animal skin. One of the most common, and the one from which the word tanning derives, is tannin. Tannin is a naturally-occurring substance found in tree bark. It produces a firm form of leather which is usually browny in colour. Chrome tanning is done using chromium salts. It results in a more supple form of leather than vegetable tanning, and chrome-tanned leather can more easily be colourised. Other substances such as alum, wax, or even animal brains can also used to turn animal skins into leather.
