Mordant

For the type of musical ornament mordent (note the different spelling), see Ornament

A mordant is a substance used to set dyes. A mordant is either inherently collodial or produces colloids and can be either acidic or basic.

Mordants include tannic acid, alum, chrome alum , and certain salts of aluminum, chromium, copper, iron, iodine, potassium, and tin.