Mordant is preparing wool for absorbing dyes. It is as important as dyeing.

The first mordant, used for natural dyeing, were natural substances and had dyes by themselves or were with tannin.

After that, steel mordant were discovered, so herbal mordant had not been important anymore.

Today, tannin is mostly used in black or dull colors. Usually, mordant increases absorption of dye on thin pile or wool.