Water soluble tannin for cotton mordanting and black. Also used as a beige base for block printing with an iron solution.
Use at 20 to 25% by weight of fabric. A cold soak overnight, with a few stirrings, is usually adequate to impart a good beige base to any natural textile fiber. In cotton dyework, a combination of alum mordant with a tannin base gives the richest and most permanent colours.