Making colour
Natural dyeing and mordants
Most plant dyes wash out unless the cloth is treated with a metal salt called a mordant. Alum and iron are the usual ones.
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A mordant is a substance that fixes a dye to cloth. Most natural dyes will not hold on their own: they wash out or fade. Treating the fibre with a metal salt, usually alum or iron, gives the dye something to grip. The mordant also changes the colour. The same madder root can give pink, red, purple or brown depending on the mordant used.
How a mordant works
The word comes from the French for to bite. A mordant is usually a salt of aluminium, iron, copper or tin. Its metal atoms attach to the fibre and to the dye molecule, forming a bridge between them. Alum, an aluminium salt found as a natural mineral, gives clear, bright colours. Iron darkens, or saddens, a colour, turning yellows to olive and reds to purple or brown. Tannins from bark, leaves and nuts help mordants hold on cotton. Indian dyers use myrobalan, the dried fruit known in Hindi as harad.
Printing with mordants
Indian cotton printers worked out long ago that if the mordant is painted or block-printed on the cloth, and the whole cloth is then dipped in one dye bath, colour appears only where the mordant is. Alum in one place and iron in another give red and black from a single madder bath. Further steps with wax and indigo add blue and green. This is the method behind kalamkari, ajrakh and the chintz that was traded around the Indian Ocean and to Europe. Malian bogolanfini, or mud cloth, uses iron-rich mud on cloth soaked in tannin.
Dyes that need none
A few dyes fix themselves. Indigo works by a different chemistry: it is dissolved in a vat without oxygen and turns back into an insoluble blue inside the fibre when the cloth meets the air. Turmeric and some lichens colour cloth directly, but not always lastingly. Natural dyeing is having a revival among craft dyers and small clothing makers. It is not automatically gentle on the environment. It uses a great deal of water and plant material, and some traditional mordants, such as copper and chrome salts, are harmful.
How to do it
- Wash the yarn or cloth thoroughly to remove oils and finishes.
- Simmer it in a mordant bath, most often alum, then rinse.
- Simmer the dye material, such as onion skins or madder root, in water and strain it.
- Put the damp cloth in the dye bath and heat gently until the colour is deep enough.
- Rinse, dry in the shade and wash separately the first few times.
Colours on this page
Sources and further reading
- Mordant on Wikipedia
- Online Etymology Dictionary: mordant
- Getty Publications: The Matter of Madder in the Ancient World
- Sahapedia: Kalamkari
Original text by the Rang desk, written with AI assistance and checked against the sources above. Meanings of colour vary from place to place and person to person. If we have something wrong, tell us.