Indigo: The Color That Built Trade Routes, Fueled Wars, and Made Blue Cheap

Indigo blue is one of the oldest dye substances used by humans, with evidence of its use in Peru dating to 6,000 years ago and in Egypt to approximately 4,400 years ago. The dye is derived from the indigofera plant genus, of which dozens of species exist across tropical and subtropical zones, but the specific mechanics of how a colorless precursor compound (indican) in the plant's leaves is converted to the insoluble blue pigment through fermentation and oxidation were not fully understood until the nineteenth century. For most of its history, indigo was a practical craft knowledge rather than a chemistry. The importance of indigo in global trade cannot be overstated. The British East India Company's control of Indian indigo production in Bengal was a commercial operation of enormous scale. Indian indigo — produced by the subspecies indigofera tinctoria — was chemically superior to European woad, the native blue dye plant that had dominated European cloth dyeing before the trade routes opened. The competition between Indian indigo and European woad was not just commercial but political: European rulers in the fifteenth and sixteenth centuries banned Indian indigo specifically to protect domestic woad producers, with Germany and France imposing the death penalty for importers of what was officially classified as the Devil's dye. The indigo economy of colonial South Carolina and later of British India's Bengal province was built on forced labor. In South Carolina, enslaved Africans from the rice-growing regions of West Africa were specifically acquired for their knowledge of cultivation and processing techniques. In Bengal, the indigo plantation system — the neel chaash — forced peasant farmers to grow indigo on a portion of their land at below-market prices, a system that produced the Indigo Revolt of 1859, one of the first significant organized peasant uprisings against colonial agricultural exploitation. The synthesis of indigo in the laboratory by Adolf von Baeyer in 1878 — and its commercial production by BASF beginning in 1897 — collapsed the natural indigo market within a generation. The price of blue dropped precipitously, making it accessible to mass clothing production for the first time. Levi Strauss had been producing blue denim work trousers since 1873 using natural indigo; the shift to synthetic indigo in the early twentieth century made blue denim an everyday garment rather than a specialized workwear product. The democratic blue of blue jeans is, in part, the consequence of the chemical synthesis of a commodity color.