True blue blooms, as gardeners know, are hard to find. No less for our ancestors searching for such a source to dye both textiles and themselves.
A reliable blue was discovered at least 6,000 years ago, in various species of Indigofera, a genus of some 700 species of leguminous annual and perennial herbs, shrubs and small trees native to tropical and warm regions. The major natural dye source has been I. tinctoria, a deciduous subshrub with pink and blue flowers originating in southeast Asia.
This is not the only Indigofera that has been used to yield blue dyes. In fact, a South American species, I. fruticosa, appears to have been used by the inhabitants of Peru’s Huaca Prieta at least 1,600 years prior to indigo-sourced dyes in Egypt 4.400 years ago, and in China 3,000 years ago.
This has intrigued researchers. Processing requires several steps to extract the dye from its plant source. These include soaking and fermenting leaves to produce a colourless substance before stirring the mixture in the open air, which eventually yields the main blue-dye component, explained Bruce Bower in Science News. He quotes archaeologist Jeffrey Splitstoser: “What surprised me is that the indigo dye process was discovered at all and developed independently in so many parts of the world.”
Even in this modern age, travelers flying into Kano, the principal city of northern Nigeria, are puzzled to see dark round holes below them. These are the communal dye pits of Hausa dyers, for millennia an industry producing dyed textiles traded across the Sahara and Sahel to the south.
Another, and equally famous blue was the woad of the ancient Celts. Perhaps surprisingly a member of the cabbage family, Brassicae, Isatis tinctoria is native to Caucasus and the Steppes to eastern Asia but seeds have been identified found in Neolithic sites in Europe. Julius Caesar De Bello Gallico that the Britanni coloured their bodies blue with vitrum, which has been translated as woad, but this has been disputed. So perhaps the picture of naked blue-dyed Brits hurling insults from the Channel cliffs onto Cesar’s landing legions lacks some accuracy. It is only fair to add that, having been transported to North America, it has become a noxious weed in the western U.S.
There are two plants called dyeweed, it’s true;
The second’s called woadwaxen too.
It’s a flowering weed
To which few folks pay heed,
And there’s not much to see if they do.
Back to indigo: In recent times, it has found use to dye denim for jeans and as a food colourant. It requires anywhere from three to 12 grams to dye a single pair of jeans. The continued popularity of the garments calls for an annual production of about 20,000 tons.
Wes Porter is a horticultural consultant and writer based in Toronto. Wes has over 40 years of experience in both temperate and tropical horticulture from three continents.
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