When exposed to air, it converts to a ferric tannate, which is a darker pigment. Albumin tannate (also known as "Tannin albuminate") is an antidiarrheal. Other orally available salts are the hydrochloride and the tannate; suppositories contain the free base. A tannate is the salt or ester of tannic acid. By mixing tannin with iron sulfate, a water-soluble ferrous tannate complex is formed.