Indigo and Natural Indigo Dye
1. Dyeing with Indigo
Indigo is sold as a dark blue crystalline powder and is not soluble in either water or alcohol. First you need to make it soluble in an alkaline vat where oxygen has been removed either by fermentation or with a suitable chemical. You then dip your fibre in the vat and the soluble indigo combines with the fibre. When you expose the fibre to oxygen in the air you will see it gradually change colour from pale yellow to green and then finally to blue, as the indigo dye reverts to its insoluble blue form. Seeing the colour develop in the air must have looked like magic to many early cultures, and this change in colour can easily get you hooked on dyeing blues (read more on recipes for indigo dyeing).
Indigo is light-fast and does not require fibre to be mordanted beforehand, making it easier for you to dye cotton than most other natural dyes.
Indigo is also ideal for use in batik; unlike many other natural dyes that require a high temperature, indigo works at low temperatures and does not melt batik wax. It works quickly and you can get blue fabric after just 10 minutes in the indigo vat. Speed is useful for tie dye and shibori as there is not enough time for the dye to spoil the pattern by penetrating under the ties.
Using just indigo and a resist technique such as shibori or batik, you can create countless blue and white patterns with timeless appeal. Indigo, however, is a base for many other colours. It is almost essential for good greens and blacks and you can produce a wide range of greens by overdyeing indigo with yellow dyes such as weld or Persian berry. For attractive violets, purples and mauves, overdye it with madder or cochineal. Very dark indigo overdyed with madder and sometimes gallnut or iron produces good blacks.
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2. Types of Indigo Plants
Much of the world has native plants that produce indigo and more than fifty different species of plants produce indigo in usable quantities. Indigo-bearing plants come from families as diverse as the bean family (leguminosae), cabbage family (cruciferae) and rhubarb family (polygonaceae). Examples of indigo-bearing plants include several species of Indigofera, Japanese indigo (Persicaria tinctoria), woad (Isatis tinctoria), dyer’s oleander (Wrightia), Strobilanthes and Marsdenia. You can read in more detail about these and other sources of indigo in an excellent book by Dominique Cardon, “Natural Dyes, sources, tradition, technology and science”.
Most natural indigo dye for sale comes from the leaves of Indigofera tinctoria. This plant is tender to frost and grows best in the tropics, thriving in hot and humid places with fertile soil. It is commercially grown in India, El Salvador, Vietnam and some other countries. It is an annual or perennial, 2 m tall, and has compound leaves with many oblong leaflets. The leaves close at night and spread open again at dawn (read more on growing indigo).
As much as 20 tonnes of leaves are needed to produce just 45 kilos of pigment and unlike other natural dyes, indigo is not present in the plant. Only the chemical precursor of indigo is present and you need to process the leaves to produce the indigo powder. Although you need to follow the instructions carefully, it is not difficult to extract your own indigo if you harvest the leaves at the right time (read more on indigo extraction).
3. Indigo History
Indigo is an ancient dye and there is evidence for the use of indigo from woad or Indigofera from at least the third millennium BC, and possibly much earlier for woad (read more about the history of indigo).
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4. Natural Indigo versus Synthetic Indigo
Although the chemical formula for natural and synthetic indigo is the same, synthetic indigo is almost pure indigotin. Natural indigo has a high proportion of impurities such as indirubins, that give beautiful colour variations. Like fine wines, the blue you get depends on where the indigo was grown and the weather at the time. Synthetic indigo on the other hand, produces an even blue that never varies.
Natural indigo is a sustainable dye; after the pigment has been extracted the plant residue can be composted and used as a fertiliser and the water reused to irrigate crops. Natural indigo can often be traced to its country of origin, and even to the farm where it was produced. In buying it, you will be helping to give sustainable employment to rural population in developing countries. Synthetic indigo on the other hand is extracted from petrochemicals and its manufacture produces hazardous waste. By using natural indigo, you will be helping the environment and reducing the use of petrochemicals.
Natural indigo is the ideal blue dye to use on handmade textiles and on natural fibres; it may cost a little more than synthetic indigo, but the main cost of handmade items is time. Natural indigo is also essential for living history research, and for historic re-enactments. This may seem obvious, but if you want to use natural dyes, you need to use natural indigo rather than synthetic. Synthetic indigo is not a natural dye. Sometimes dyers may be unaware that they are in fact using synthetic indigo, as some shops don’t always make it clear what type of indigo they are selling. If in doubt, check with your supplier!
1. Why use Indigo?
2. Mayan Indigo from El Salvador - NEW
3. Growing & Harvesting Indigo
4. Dyeing with natural Indigo
5. Dyeing with Indigo crystals
6. Gallery of indigo-dyed cotton samples
7. History of Indigo
8. Indigo Chemistry
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