Tannic Acid is an organic substance with the chemical formula C76H52O46, which is a tannin derived from gallnut. It is yellow or light brown light non-crystalline powder or scale; odorless, slightly special smell, very astringent taste. It is soluble in water and ethanol, easily soluble in glycerin, and almost insoluble in ether, chloroform or benzene. Its aqueous solution turns blue-black when it meets with iron salt solution, and sodium sulfite can delay the change of color. In industry, tannic acid is widely used in leather tanning and blue ink production. Tannic acid can coagulate protein. People chemically treat raw pig skins and raw hides with tannic acid, which can coagulate the soluble protein in the raw hides. As a result, the raw hides that would stinks and rot after a few days have become beautiful, clean, flexible, and durable leather. This tanning process is called leather tanning.