Guimarães IV

The past, tanning.
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 also possibly coloring it.
Before tanning, the skins are unaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days. Historically this process was considered a noxious or "odoriferous trade" and relegated to the outskirts of town. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name (tannin is in turn named after an old German word for oak or fir trees, from which the compound was derived). The use of a chromium (III) solution was adopted by tanners in the Industrial Revolution.
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 India between 7000 and 3300 BC. Around 2500 BC, the Sumerians began using leather, affixed by copper studs, on chariot wheels.