Indigo is the forgotten dye. But a group of enthusiasts are determined to revive it. By John Windsor
Joss Graham handed me a strip cut from a Tuareg turban. "Smell it," he said. "Wonderful, isn't it." The strip of coarse cotton glistened with indigo of the deepest blue. It smelled like schoolroom wax crayons. I was later to learn that some age-old indigo-dyeing processes use human urine.

Indigo, for millennia the most gorgeous dye known to man, all but disappeared from our colour palette at the turn of the century, made obsolete by synthetic dyes.

The original jeans, patented by Levi-Strauss in America in 1873, used natural indigo, imported from Nimes (hence denim: "de Nimes"). But soon every good cowboy and gold-panner wanted a pair, and synthetic indigo, which gives the same faded quality but is cheaper, was used instead.

But synthetic indigo lacks the romantic appeal of the natural dye. It is a miracle, says Mr Graham, that indigo, the only natural pigment known to hold fast in fabrics, should be blue - "the colour of the deep of the sea, of the firmament above, of inner peace. There is so little blue on land. Such a miracle that it should be found in a plant."

A miracle, too, that every climate should yield its own version of the shock-headed indigo bush. In Europe it is woad.

Mr Graham describes himself as a guardian of historic textiles. He imports native items, including indigo-dyed fabrics and garments, some of which have been snapped up by the British Museum and the V&A. "The analogy between an endangered species and the indigo dyeing process is a real one," he says.

With missionary zeal, he and other followers of the King of Colours have made pilgrimages to villages in India, Africa and the Middle East and bent the knee before the last toothless old women capable of concocting the magic brew.

For British seekers, Mr Graham has mounted a selling exhibition of indigo- dyed textiles at his shop inVictoria, London, coinciding with the Art of African Textiles exhibition at London's Barbican.

Secret recipes will be revealed by Nike Olaniyi Davies, who has a school of 180 dyers in Oshogbo, Nigeria. Visitors to the exhibition will be invited to plunge garments into one of her two bubbling dye-baths in the shop's garden.

Historic indigo-dyed costumes at the exhibition are the most expensive: an Indonesian hinggi, or man's cloak, patterned with cockerels and two- headed lizards, collected by a Kew botanist in 1956, is pounds 750.

Less expensive are textiles from Mr Graham's own indigo-dyeing redevelopment scheme, in Rajasthan, India. He commissions block-printed fabrics in long-forgotten, swirling patterns - from pounds 29. Rajasthani scarves and skirts with tiny tie-dyed patterns are pounds 22.50 and pounds 60.

"If these traditional craftsmen don't get orders from us," he says, "they will forget their skills and join the urban poor in factories."

Meanwhile, in her Devon cottage, Dr Jenny Balfour-Paul, the exhibition's lecturer on indigo history, is fermenting bubbling concoctions of her own in four old-fashioned glass sweet-jars. They are filled with home- grown indigo and woad - and stale human urine. Her 15-year-old son now refuses to contribute, so she supplies her own. "My children think I'm revolting," she says.

Indigo's miraculous ability to become "fast" in fabrics is due to an enzyme in its leaves that, when fermented, produces a dye that is at first insoluble. Fabrics will not absorb it. This is where urine and wood ash come in. They are alkaline "reducing agents": they expel oxygen, making the indigo soluble. Fabrics absorb it readily. Then, when re-exposed to the air, the dye in the fabric resumes its insoluble state. It becomes fast.

The beauties unique to indigo come from repeated dipping - giving depth of colour ranging from pale blue to blue-black - and decoration using techniques such as masking with clay or wax. One garment in the exhibition decorated by such a "resist" technique is a 9ft x 5ft Nigerian wrap with animal pictures applied with chicken feathers dipped in cassava paste (pounds 120).

Dr Balfour-Paul began "trying desperately to record the last of the indigo trade" after visiting the town of Zabid in Yemen in 1983, where she was shocked to find that the 150 indigo workshops of 1960 had dwindled to just two.

"The ecologically-minded in developed countries will support the indigo industry," she believes. "Unlike the chemical dye process, you can keep an indigo vat going for months, without ever having to tip out nasty chemicals such as caustic soda."

She is awaiting the results of European Commission research into the use of set-aside land to grow woad and hemp. Who knows - it might have cult appeal.

"Indigo", Joss Graham Gallery, 10 Eccleston Street, London SW1. They will be running indigo dyeing classes over the next two weeks, call 0171-730-4370 for details. The Art of African Textiles, Barbican Art Gallery, 4 Oct-21 Jan.