Unlike blue pigments, blue indigo dye was far more accessible in the ancient world and to the common man.

The Romans imported cheap indigo blue dye, making blue the color of working-class clothing, with colors like black, red or violet worn by the nobility. (White was also a color worn by the wealthy, but that was because of the upkeep it required.)  Blue was also considered a color of mourning, and the color of barbarians.

Celts and Picts and Germans were said to have dyed their faces blue to frighten their enemies, and tinted their hair blue when they grew old. In England indigo dye was used to color clothing worn by men and women of all social backgrounds.

The earliest European source of indigo dyes was woad.

 Woad

The flowering plant Isatis tinctoria, also called woad, glastum or Asp of Jerusalem grows throughout Europe, especially Western and Southern Europe Its leaves produce a distinct blue indigo dye. Woad growing regions in medieval England, Germany and France became prosperous from the woad trade.

Woad (blue), along with madder (red) and weld (yellow), was one of three staple dyes of the medieval European dyeing industry. Tapestries like The Hunt of the Unicorn series (1495-1505) feature fibers dyed with woad. A woad-based ink was also used to illustrate medieval manuscripts.

Indigo from other sources.

Indigo is the dye chemical extracted from woad. Interestingly, the same dye can be extracted from another plant, sometimes called “true indigo”, Indigofera tinctoria. “True indigo” produces the dye in higher concentrations than the woad plants prevalent in Europe. As far back as 4000 BC, evidence for use of this color can be found in Peru. True indigo plants were also cultivated in East Asia, Egypt and India.

Indigo disrupts the textile trades

After the Portuguese discovery of a sea route to India in 1498, indigo (from true indigo) began to be imported from Asia. The better colorfastness of imported indigo made it a serious competitor in the blue dye market. By 1577, governments began to intervene by denouncing imported indigo as damaging and even going to far as to prohibit its use. Even so, indigo was a highly desired import during the 17th and 18th centuries. The dye drove trade wars between European nations and the Americas, fueled the African slave trade, and even partially funded the American Revolutionary war.

Indigo in the spectrum

Astute readers will recognize ‘indigo’ as one of the colors of the ROYGBIV spectrum developed by Sit Isaac Newton. Less well known are the reasons for indigo’s inclusion in the spectrum. It seems Newton believed that since there were seven days in the week, seven known planets (at the time), and seven notes on the (western) musical scale, there should also be seven colors in the spectrum. Never mind the annoying little fact that there only seemed to be five unique colors, Newton pushed orange and indigo into the spectrum to achieve his desired seven colors.

Synthetic indigo

German chemist Von Baeyer developed a synthetic indigo in 1878. By the end of the WWI, the synthetic product had replaced natural indigo and brought an end to the natural indigo trade from the East and West Indies. In 1901, Indanthrone blue, another synthetic indigo, which had greater fade resistance, captured the market. Today nearly all blue jeans are dyed with this product.

But that may not be true for much longer. Scientist have engineered an Escherichia coli bacteria to produce the chemical reaction that creates natural indigo. Called “bio-indigo”, it could be the next, environmentally friendly, chapter in the story of indigo and the history of blue.

References

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