Tannic acid

Tannic acid, or tannin (C₇₆H₅₂O₄₆), organic substance extracted from the bark of certain trees (e.g., oak, hemlock, and chestnut). In a process known as tanning, tannin is added to animal hides to resist decomposition. Tannin is also used to manufacture inks and is used as a fixative (mordant) for dyes. It can also be used as a medicine for treating burns and as an astringent. Most of the tannin used in the United States today is obtained from the quebracho trees of Argentina and Paraguay.