Picture 1.
Iron mordant ( ferrous sulfate)

Mordant can alter the hue and intensity of natural dyes. By using different mordant's, a variety of shades and colors may be obtained from a single dyestuff. For example in last week's article, a single logwood dye can create red purple, blue purple, blue grey, grey, or black by using different type of mordants.

The mordant commontly used with the natural dyestuffs are alum (aluminium potassium sulfate), chrome (potassium dichromate), copperas (ferrous sulfate), and tannic acid or some other source of tannin such a soak galls or sumach leaves. 1

1 Adrosko, Rita J. Natural Dyes and Home Dyeing
Dover Publications, Inc., 1974

Each fabric or yarn has different properties regarding their ability to absorb mordant into their fibers. Wool's and silk's are some of the fibers that retain chemicals in their fibers well. Cotton or other vegetable fibers that do not absorb mordant easily may require a special chemical such as tannic acid as a mordant or as an agent for fixing mordants in the fiber.

Picture 2.
Undyed cotton thread and logwood cotton thread

The process of natural dyeing may sound complicated, however, the logic behind the process is simple. Once the fabric has been treated with the mordant, combine the dyestuff to set the color. The fabric absorbs the mordant, and the mordant absorb the dyestuffs. You then have a permanent color.