Tannic acid, also called tannin, is a group of chemical substances found in the bark, leaves, fruit, roots, and other parts of many trees. Tannin is obtained from such trees as oaks, mangroves, wattles, chestnuts, hemlocks, and quebrachos.
Tannins are used to tan animal hides. The hides contain collagen, a protein that holds tissue together. The collagen combines with the tannin, converting the hides to leather. Tannins are also used as mordants (dye fixatives) and in manufacturing inks.
Tannins from different sources have different chemical formulas. Most of the tannin used in the United States comes from quebracho trees that grow in Argentina and Paraguay. This tannin is a thick, reddish-brown liquid, which may be dried to form a hard cake.
