what is a mordant

A mordant is a substance used to set dyes on fabrics or fibers by forming a coordination complex with the dye, which then attaches to the fabric or fiber. The term "mordant" comes from the Latin word "mordere," which means "to bite". The use of a mordant helps to ensure the most durable and long-lasting colors, and it enhances the wash- and lightfastness of the dyed yarn or fabric. Mordants can be either acidic or alkaline, and they are often polyvalent metal ions, such as chromium (III) . Some common mordants include tannic acid, oxalic acid, alum, chrome alum, sodium chloride, and certain salts of aluminum, chromium, copper, iron, iodine, potassium, sodium, tungsten, and tin. Different mordants can perform better or worse on different kinds of fibers, such as cellulose fibers (e.g., cotton, linen, and bamboo) and protein or animal fibers (e.g., wool, cashmere, alpaca, and silk) . There are three methods used for mordanting: pre-mordanting, meta-mordanting, and post-mordanting. The type of mordant used affects the shade obtained after dyeing and also affects the fastness property of the dye.