Whats the difference between mordants and other chemical assistants used in dyeing?
Sodium carbonate is not a mordant! Neither are vinegar or salt. A mordant is a metal ion which attaches to the fiber, usually by being boiled together for a length of time. A dye which has no natural attraction to the fiber can then attach to the metal ion. Most but not all natural dyes are mordant dyes, which require the metal ion to be in the fiber in order for them to have any attraction to the fiber. There are also some synthetic dyes that are mordant dyes. Mordants include alum, chromium, copper, iron, and tin. Some of these metals are quite toxic and hazardous, in addition to be environmentally damaging. Chromium is the most hazardous of mordants. The hexavalent form of chromium, in potassium dichromate, which called for in some recipes, is a known human carcinogen. Alum is the least toxic of the mordants, though it can be irritating and should be used with care. Tannic acid is another important mordant, a large, complex, metal-free molecule, used mainly in dyeing cellulose fiber
