Then the wet, pre-mordanted material to be dyed is steeped in the hot bath until the desired color has been obtained. To enhance the learning process, the dyer should be careful to label the product of each experiment and to keep complete records. Natural dyes work best with natural fibers such as cotton, linen, wool, silk, and others such as jute, ramie, and sisal. Carol Leigh works almost exclusively with wool and finds a good deal of contrast in dye take-up between different breeds of sheep and even variances in the coarseness of the fibers from the same fleece. Most important of all is the choice of mordant.
Mordants are chemicals that help improve the depth of color and the fastness of the dye.
The most commonly used mordants are the metallic salts of alum, chrome, iron, and tin. The chosen mordant and the way it is used depends on the dyestuff, the fiber being dyed, and on the color desired. She frequently obtains eight or more harmonizing colors from one dye bath by dying several batches of wool, each previously prepared with a different mordant. Tin is caustic to the skin. You must use common sense and dump both the mordant and dye bath where no pets or children can get to it.