In the dyeing terminology mordants are substances used to improve the absorption of colors by the outer surface of the wool and ensure fastness of the colors, when exposed to sunlight or water.

The outer surface of the wool has the characteristic of being waterproof and thus resistant to color absorption. The use of special chemical substance considerably reduces and even eliminates this color resistant layer and improves the darkness and lightness of the dye.

Therefore, as a first step, the wool is treated with mordants before it is immersed in the dyeing tanks.