Natural Dyes - Processes

Processes

For more details on this topic, see Glossary of dyeing terms.

The essential process of dyeing requires soaking the material containing the dye (the dyestuff) in water, adding the textile to be dyed to the resulting solution (the dyebath), and bringing the solution to a simmer for an extended period, often measured in days or even weeks, stirring occasionally until the color has evenly transferred to the textiles.

Some dyestuffs, such as indigo and lichens, will give good color when used alone; these dyes are called direct dyes or substantive dyes. The majority of plant dyes, however, also require the use of a mordant, a chemical used to "fix" the color in the textile fibers. These dyes are called adjective dyes. By using different mordants, dyers can often obtain a variety of colors and shades from the same dye. Fibers or cloth may be pretreated with mordants, or the mordant may be incorporated in the dyebath. In traditional dyeing, the common mordants are vinegar, tannin from oak bark, sumac or oak galls, ammonia from stale urine, and wood-ash liquor or potash (potassium carbonate) made by leaching wood ashes and evaporating the solution.

We shall never know by what chances primitive man discovered that salt, vinegar from fermenting fruit, natural alum, and stale urine helped to fix and enhance the colours of his yarns, but for many centuries these four substances were used as mordants.

Salt helps to "fix" or increase "fastness" of colors, vinegar improves reds and purples, and the ammonia in stale urine assists in the fermentation of indigo dyes. Natural alum (aluminum sulfate) is the most common metallic salt mordant, but tin (stannous chloride), copper (cupric sulfate), iron (ferrous sulfate, called copperas) and chrome (potassium dichromate) are also used. Iron mordants "sadden" colors, while tin and chrome mordants brighten colors. The iron mordants contribute to fabric deterioration, referred to as "dye rot". Additional chemicals or alterants may be applied after dying to further alter or reinforce the colors.

Textiles may be dyed as raw fiber (dyed in the fleece or dyed in the wool), as spun yarn (dyed in the hank or yarn-dyed), or after weaving (piece-dyed). Mordants often leave residue in wool fiber that makes it difficult to spin, so wool was generally dyed after spinning, as yarn or woven cloth. Indigo, however, requires no mordant, and cloth manufacturers in medieval England often dyed wool in the fleece with the indigo-bearing plant woad and then dyed the cloth again after weaving to produce deep blues, browns, reds, purples, blacks, and tawnies.

In China, Japan, India, Pakistan, Nigeria, Gambia, and other parts of West Africa and southeast Asia, patterned silk and cotton fabrics were produced using resist dyeing techniques in which the cloth is printed or stenciled with starch or wax, or tied in various ways to prevent even penetration of the dye when the cloth is piece-dyed. Chinese ladao is dated to the 10th century; other traditional techniques include tie-dye, batik, Rōketsuzome, katazome, bandhani and leheria.

The mordants used in dyeing and many dyestuffs themselves give off strong and unpleasant odors, and the actual process of dyeing requires a good supply of fresh water, storage areas for bulky plant materials, vats which can be kept heated (often for days or weeks), and airy spaces to dry the dyed textiles. Ancient large-scale dye-works tended to be located on the outskirts of populated areas, on windy promontories.