2. Tanning and Dyeing
It's a process which makes leather flat.
Skins and leather: "skin" becomes "leather" after it goes through a tannage process.
Animal leather is supposed to be the best material for footwear because of its breathability, softness, elasticity and resilience.
Tanning is the process to treat animal skin chemically with a tanning formula, which makes it into leather.
There are vegetable and mineral tanning materials. A vegetable tannage uses tannin extract, which occurs naturally in a variety of tree barks. Mineral tannage uses a chemical called chromium sulphate.
Dyeing is a process which colors tanned leather.