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 …