Before we apply any natural dyes, we must prepare our fabrics for dyeing by mordanting them. “Mordant” comes from an Old French word meaning “to bite”, and the non-toxic mordants with which we treat our fabric chemically “bite” into the fibers, creating spots for the natural dyes to attach firmly to the fabric. (In keeping with the theme of “biting into things”, Ali likes to liken the mordanted and dyed fabric to a peanut butter and banana sandwich, with the fabric as a slice of bread, the mordant as peanut butter, and the natural dyes as delicious slices of banana sitting on top.)
Certain dye sources such as indigo, our main source of blue pigment, produce colorfast dyes without any assistance. These ‘vat dyes’ rely on processes of reduction by fermentation and oxidation to create lasting color over several steps. Most plant dyes, however, utilize a mordant to permanently set color in the fiber. This chemical, typically separate entirely from the plant dye, combines with the dye to attach the coloring matter to the fiber by increasing affinity and/or strengthened interactions via a lasting chemical bond. This mordant makes the color wash and light fast, able to persist over time with wear.