Alum Mordant Bath: Tannin fabric on left of pot (slightly darker).
Step Three: A second mordant bath of Alum Acetate. A "mordant" functions as a chemical bridge, binding to both the dye and the fabric more effectively than either can bind to the other. Making the dye permanent. A lots of natural plants or flowers can produce color, but will not last through light exposure or washings. Mordants can also shift the color of the dye.