Tanning (leather)

Tanning is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed. Tanning hide into leather involves a process which permanently alters the protein structure of skin, making it more durable and less susceptible to decomposition and coloring. Before tanning, the skins are dehaired, degreased, desalted and soaked in water over a period of six hours to two days. Historically this process was considered a noxious or "odoriferous trade" and relegated to the outskirts of town. Historically, tanning used tannin, an acidic chemical compound derived from the bark of certain trees. An alternative method, developed in the 1800s, is chrome tanning, where chromium salts are used instead of natural tannins. The English word for tanning is from medieval Latin tannāre, derivative of tannum (oak bark), from French tan (tanbark), from old-Cornish tann (oak). These terms are related to the hypothetical Proto-Indo-European * meaning 'fir tree'. (The same word is source for Old High German tanna meaning 'fir', related to modern Tannenbaum). Despite the linguistic confusion between quite different conifers and oaks, the word tan referring to dyes and types of hide preservation is from the Gaulic use referencing the bark of oaks (the original source of tannin), and not fir trees. Ancient civilizations used leather for waterskins, bags, harnesses and tack, boats, armour, quivers, scabbards, boots, and sandals. Tanning was being carried out by the inhabitants of Mehrgarh in Pakistan between 7000 and 3300 BCE. Around 2500 BCE, the Sumerians began using leather, affixed by copper studs, on chariot wheels. Formerly, tanning was considered a noxious or "odoriferous trade" and relegated to the outskirts of town, among the poor. Indeed, tanning by ancient methods is so foul-smelling that tanneries are still isolated from those towns today where the old methods are used. Skins typically arrived at the tannery dried stiff and dirty with soil and gore.