The mushrooms are crushed and placed in a non-reactive pot to simmer for as long as desired or until you achieve a desired depth of color. Mushrooms that can be used without a mordant are called "substantive dyes", but in order to improve color and light fastness a mordant (metallic salts) can be used. Protein fibers, like wool and silk, quickly take the dye, but cotton, hemp and some synthetic fibers can be used too[14].