 Tannins are an important ingredient in the process of tanning leather.Tanbark from oak, mimosa, chestnut and quebracho tree has traditionally been the primary source of tannery tannin, though inorganic tanning agents are also in use today and account for 90% of the world's leather production.Tannins produce different colors with ferric chloride (either blue, blue black, or green to greenish-black) according to the type of tannin.