Indigo is a rich blue dye that was widely used throughout the ancient world, from Indonesia to Europe. The distinctive dark blue color has made this dye famous, with a variety of synthetics being used today to produce indigo which is colorfast and fade-resistant, in contrast with that of natural origins used historically. Many craft stores sell it in their dye sections for people who want to work with this dye directly.
The earliest records of indigo date to around 1600 BCE, and seem to suggest that the use of this dye probably originated in India, spreading out to the Middle East and China and diffusing from there. In fact, the name comes from the Latin indicum, which means “of India.” Indigo quickly became a very popular color thanks to its depth and saturation, which made wool, cotton, and linen garments incredibly dark.
This dye was historically sourced from plants in the genus Indigofera, a member of the pea family native to Asia. Indigo could also be extracted from woad, as it was in the British Isles, and from some shellfish in the genus Murex, also used by the Phoenicians to make another famous dye, Tyrian Purple. The compound that creates the blue color is actually not soluble in water, so in order to turn it into a dye, people had to subject it to chemical treatments. Some of these treatments were quite harsh, leading to health problems at textile manufacturing facilities and occasionally attracting attention from social reformers.
Historically, many people simply soaked their indigo in stale urine to turn it into a dying compound, leading dyemakers to be exiled to the fringes of cities in some regions due to the smell. Indigo could also be fermented to make a dye, as was done in Asia, and some people simply painted it directly onto substances they wished to dye. Textiles also had to go through multiple dye cycles for the color to take, and it usually only penetrated the upper layers, leaving behind a white core.
Since 1900, most companies that want to work with indigo use synthetic dyes. These dyes are stronger than the natural ones, and also more predictable, ensuring that batches retain consistent coloration. Denim is one famous product traditionally made with indigo; the distinctive wear of jeans is the result of the wear patterns of the dye, which naturally fades out through repeated washes.