A mordant's a substance used to set dyes on fabrics by forming an insoluble compound with the dye. It may be used for dyeing fabrics, or for intensifying stains in cell or tissue preparations. A mordant's either inherently colloidal or produces colloids and can be either acidic or alkaline. Common mordants Mordants include tannic acid, alum, chrome alum, sodium chloride, and certain salts of aluminum, chromium, copper, iron, iodine, potassium, sodium, and tin. Iodine's used as a mordant to set… (More on Mordant)