Indigo dye
The world's favorite blue dye comes out of the vat yellow-green and turns blue in the air.
- Made from
- Indigofera leaves (also woad); now synthetic
- Synthesis
- Baeyer 1878–80; BASF commercial 1897
- Name
- Greek indikon, 'from India'
Indigo is the blue of jeans, and one of the oldest dyes on earth. The oldest known indigo-dyed cloth, about 6,000 years old, was found at Huaca Prieta in Peru. The main source plant, Indigofera tinctoria, was domesticated in India, and the Greek name indikon, 'from India', became our word indigo. Europe used a plant with the same dye, woad, until sea trade brought cheaper Indian indigo; woad interests got it restricted in parts of 16th-century Europe.
Dyeing with it is a small miracle. Indigo doesn't dissolve in water, so dyers ferment or chemically reduce it into a soluble, yellowish 'white indigo'. Cloth dipped in that bath comes out yellow-green, then turns blue before your eyes as air oxidizes the dye back. Each dip adds a layer, which is why indigo goes from pale sky to near-navy.
Its history is also one of forced labor and revolt: plantations in the Americas were worked by enslaved people, and in 1859 Bengal's indigo farmers rose against European planters. Then chemistry took over, as it had for purple with mauveine. Adolf von Baeyer synthesized indigo in 1878–80, and by 1897 BASF sold synthetic indigo at scale. Natural production collapsed within two decades.
Today most indigo is synthetic, and most goes into denim. It also sits inside the rainbow by accident: Newton named indigo as one of seven spectral colors, partly to match the seven notes of a scale, which is why the app's indigo is a violet-blue while the dye is a deep blue.
Swatches
- Indigo dye · many dips (approx.)
- Denim · indigo on cotton
- Leuco-indigo bath · yellow-green (approx.)
Colors
Sources
- Splitstoser, J. C. et al. (2016). Early pre-Hispanic use of indigo blue in Peru. Science Advances 2(9): e1501623.
- Balfour-Paul, J. (1998). Indigo. British Museum Press.
- Wikipedia, 'Indigo dye'.
Hex values are screen approximations. Every page lists its sources.