They are stiff, still have hair, fat and other body fluids dried onto them, and are often dirty. When skins first arrive at the tannery, they are raw. Even today, when old methods of tanning are used, tanneries are isolated from areas where people are likely to frequent. Tanning was known for its strong odors, so it was often designated an “odiferous trade” and allowed only on the outskirts of towns and cities, usually in neighborhoods where the poor lived and where other such trades were located. Sumerians were using tanned leather by 2500 BCE on their chariot wheels, attached by copper studs. We have evidence of tanning taking place in Mehrgarh (current-day Pakistan) as far back as 7000 BCE, stretching through to 3300 BCE. Of course, using hides for these purposes requires tanning. Certain treatments made leather useful for armor, quivers, scabbards and various types of footwear. The English word “tanning” comes from the Latin term tannāre, a derivative of tannum, meaning “oak bark.” From ancient times, people have used leather for the construction of waterskins, bags, clothing and even homes. An alternative method, developed in the 1800's, is chrome tanning, where chromium salts are used instead of natural tannins.

Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name, derived from the bark of specific trees. A more modern method, called chrome tanning, was developed in the 1800s and employs chromium salts instead of natural tannins to produce a similar effect. Tannin was extracted from the bark of certain trees. Tanning takes its name from the use of tannin in traditional methods. It was sometimes officially labeled a noxious or “odiferous trade.” The process can produce a lot of strong odors, especially if done in the traditional manner and without treating the off gases in some way, so historically the trade has been relegated to the outskirts of town, usually near an ample water source. This time varies according to the starting hide and the desired finished product, but ranges from as little as six hours to a couple of days. To prepare the hides for the process of tanning, the hair, grease, fat and salt is removed, and then the hide is soaked in water. The process can also entail coloring the hides or altering their feel by hardening or softening them. This process changes the skin's molecular structure to increase its durability and prevent the hides from decomposing.

To turn animal hides into a material suitable for clothing, furniture and other similar uses the hides go through a chemical process called tanning.

Tanning hides without alum