Tanning
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- This page is about making leather. For the darkening of human skin, see sun tanning.
Tanning is the process of making leather from skin. This is commonly done with the acidic compound tannin, which prevents normal decomposition and often imparts color.
Process
The process of dressing up animal skin/hide into leather consists of three stages. The first stage is the preparation for tanning. The second stage is the actual tanning and other chemical treatment. The third stage applies finishing to the surface.
In preparation for tanning, the skins (of smaller animals like goat, sheep, lamb, pig, etc) or hides (of larger animals like cow, buffalo, etc) are washed, alkali treated to remove hair and natural fat, and acidified to prepare for tanning.
The majority of leather produced today is tanned using chrome tanning material. Tanning is followed by dyeing (to give color), fatliquoring (to add fat/oil) and retanning (to fill up the fiber structure) in wet condition.
The leathers are dried and mechanically softened and prepared for finishing. Finishing is usually coating of surface with paint like mixes. Suedes, Nubucks, etc. are finished by raising the nap of the leather by rubbing with emery paper (sandpaper).
History of Tanning
In ancient history, tanning was considered a noxious trade and relegated to the outskirts of town, amongst the poor. The ancients used leather for waterskins, bags, harnesses, boats, armor, quivers, scabbards, boots, and sandals. Around 2500 BC, the Sumerians began using leather, affixed by copper studs, on chariot wheels.
Tanners would take an animal skin and soak it in water. Then they would pound and scour the skin to remove flesh and fat. Next, either they soaked the skin in urine to loosen hair fibers or they let the skin putrefy for several months, after which they dipped the skin in a salt solution. After the hair fibers were loosened, the tanners would scrape them off with a knife.
Once the hair was removed, tanners would bate the material by pounding dung into the skin or soaking the skin in a solution of animal brains. They would also take cedar oil, alum, or tannin and stretch the skin as it lost moisture and absorbed the tanning agent.
Leftover leather would be turned into glue. Tanners would place scraps of hides in a vat of water and let them deteriorate for months. The mixture would then be placed over a fire to boil off the water to produce hide glue.