Colour Project – Indigo, Part 1
Indigo is the colour named after the blue dye from the plant Indigofera tinctoria and related species. Ancient Egyptians used indigo to wrap mummies and there are indications Indigo was used in Mesopotamia 2700 years ago.
The Woad plant Isatis tinctoria produces the same indigo dye although in much smaller quantities. Woad was the main source of blue dye in Europe and Britain until Indigo was imported in Elizabethan times. Local woad growers protests ended in Indigo being banned by law for the protection of their industry. In the 1600s a death sentence was possible for those caught using indigo instead of woad. By the late 1700s the Indigo ban was lifted. Synthetic dyes later replaced Indigo only to see a revival in 1900s dye jeans.
18th Century English dyers classified Indigo (Light to Dark) inc
milk blue, pearl blue, pale blue, flat blue, middling blue, sky blue, queen’s blue, watchet blue, garter blue, mazareen blue, deep blue & navy blue
Indigo and Woad can’t be easily made into dye, oxygen must be removed from the vat by fermentation or reducing. The liquid becomes yellow -green with a deep blue metallic looking skin. The colour blue returns after re-oxygenated in the air. Successive dips and aerations are made until the right blue is achieved.
Isaas Newton in the mid-1600s introduced indigo as a spectral colour. He shone a narrow beam of sunlight through a prism to produce a rainbow-like band of colours on the wall. He acknowledged that the spectrum had a continuum of colours, but specifically named seven colours Red, Orange, Yellow, Green, Blue, Indigo and Violet “with an infinite variety of intermediate gradations”.
Sources – Wikipedia, Colour by Victora Finlay, Indigo, Egyptian Mummies to Blue Jeans by Jenny Balfour-Paul