Best Mordants to Use With Natural Dyes: There are many mordants you can choose but I believe the following are the best mordants to use when natural dyeing. One of the most important elements of natural dyeing is the use of a mordant or fixative. When dyeing protein fibers such as wool or silk, mordanting allows the dye to properly adhere to the fiber without fading or rinsing away. With plant- based (cellulose) textiles like linen or cotton, a fixative is needed to help the