Indigo
- HEX
- #3D2B8E
- RGB
- 61 43 142
- HSL
- 251° 54% 36%
- CMYK
- 57 70 0 44
Indigo or Violet?
Darker and bluer than violet.
Language
Indigo comes from Greek indikon, 'the Indian dye', because India supplied it to Europe. Its other old name, anil, from Arabic an-nil and Sanskrit nila, lives on in aniline, the chemical behind the first aniline dyes, and probably in lilac.
History
European woad and Indian Indigofera make the same blue molecule. The trade was brutal: in 1859 Bengal's farmers rose against European planters in the Indigo Revolt, and in colonial South Carolina, indigo grown by enslaved people became the second cash crop after rice. Adolf von Baeyer synthesized indigo in 1878, and BASF's factory indigo, from 1897, undercut the plantations. See indigo-dye.
Philosophy
Newton first counted five colors in his prism. In the 1670s he added orange and indigo, making seven to match the musical scale. Many people today struggle to see indigo as its own band. See spectrum.
Culture
Europe's woad growers fought the newcomer. German authorities banned indigo as 'the devil's dye' from 1577, England called it 'food for the devil', and in 1609 France threatened death for using it. The charge that indigo was corrosive or poisonous was propaganda: woad and tropical indigo make the very same blue molecule.
Science
Indigo dyes in the air. In the vat it dissolves into a yellow-green form, and cloth lifted out comes up yellowish green, then turns blue within minutes as oxygen reaches it. It needs no mordant. Built up dip by dip on the surface of the fiber, it fades with wear but never changes hue.
Kin
- Purple: Tyrian purple is indigo's molecule with two bromine atoms added
- Denim: The dye that makes jeans blue, and lets them fade
- Lilac: Same root: Sanskrit nila, dark blue
- Violet: Newton's last two rainbow colors
In paintings
- Composition VII, Wassily Kandinsky
Sources
- Wikipedia, 'Indigo dye' (Baeyer 1878; BASF 1897; Indigo Revolt 1859; Newton, Lectiones Opticae)
- Balfour-Paul, Indigo: Egyptian Mummies to Blue Jeans (2011)
- Jarman, Chroma (1994)
- Ball, Bright Earth: The Invention of Colour (2001)
- Finlay, Color: A Natural History of the Palette (2002)
- Pastoureau, Blue: The History of a Color (2001)
- Nelson, Bluets (2009)
Hex values are screen approximations. Every page lists its sources.