Two plants. Thousands of years of rivalry. And a vat that smelled of rotting fish and ammonia.
Of all the colours in the natural dyer’s palette, blue has always been the most coveted — and the most technically demanding to achieve. Before the age of synthetic dyes, only two plants could reliably deliver it: woad, native to central Asia and widely cultivated across Europe, and indigo, grown primarily in India. Their histories are intertwined, competitive, and frankly quite bizarre.
Woad: The Blue of the Ancient World
Woad (Isatis tinctoria) was the primary source of blue dye across Europe for thousands of years. The Celts famously used it to paint their bodies vivid blue before battle — an image that has persisted in popular imagination ever since. Whether the blue came from woad applied to skin or from tattoo-like patterns remains debated by historians, but the association between Celtic warriors and brilliant blue is well established.
Woad was a vat dye, which meant producing it was a complex multi-stage process. The leaves were fermented (often with the help of ammonia — from human and animal urine), turning the pigment water-soluble. Yarn was then dipped into this liquid, removed, and exposed to air, where oxidation turned it a vivid blue. The same basic chemistry governs indigo dyeing to this day.
“A historically important ingredient in an indigo vat was stale urine. The ammonia acted as a fermentation and reducing agent. Urine vats were a standard part of the dyer’s workshop for centuries.”
Indigo: The Rival That Won
Indigo (Indigofera tinctoria), grown in India, produces a far more concentrated and vivid blue than woad. Once trade routes to India were established and European markets got their first reliable supplies of true indigo, woad’s dominance began to collapse. European woad growers fought back — at various points in the 15th and 16th centuries, France, Germany and England all passed laws restricting or banning the import of indigo, sometimes labelling it “the devil’s dye” for good measure. Commerce, as usual, won out in the end.
When the indigo is dissolved in the vat, the dye bath turns a greeny-yellow colour. On the surface, air oxidises the indigo, producing the distinctive blue pigment. At the bottom sits the sediment of undissolved indigo, reducing agents and base. The transformation from yellow-green liquid to rich blue fibre — happening in real time as the yarn is lifted from the bath — remains one of the most magical moments in natural dyeing.
Shibori: Resist Dyeing and the Art of Indigo
Indigo’s cultural journey from India westward to Europe and eastward to Japan spawned one of textile history’s most beautiful art forms: Shibori. This resist-dye technique — involving folding, twisting, binding and clamping fabric before immersion in the indigo vat — travelled from China to Japan alongside Chinese dress traditions. Initially used on cheaper hemp cloth by lower social classes forbidden from wearing silk, it was eventually adopted by the aristocracy for exquisite kimono commissions.
Shibori has seen a strong modern revival among artisan and hand-dyers, many of whom still use the traditional fermentation-and-oxidation process. The look is immediately recognisable: organic, imperfect, deeply blue — and absolutely beautiful on anything from a shawl to a tote bag.
Indigo Today: From Farm to Skein
Artisan dyers today work with both indigo and woad, producing small-batch hand-dyed skeins for the knitting and crafts market. Japanese Indigo (Persicaria tinctoria) can even be grown in British gardens, and natural indigo dyeing workshops have become popular across the country. The ancient vat chemistry has not fundamentally changed in 50,000 years — though thankfully, most modern dyers have found alternatives to the urine.
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