Indigo, << IHN duh goh, >> is a deep blue dye used to color cotton and wool. It is also called indigotin. In past times, this dye was taken from the indigo plant, a member of the pea family that grows chiefly in India. The name indigo is a Spanish form of the English word India.
Large amounts of indigo began to be produced in South Carolina in the 1740’s and in Georgia in the 1750’s. The industry disappeared after the Civil War ended in 1865. Manufacturers began to make synthetic indigo, and the indigo plantations were no longer necessary.
Synthetic indigo is made from aniline, a coal-tar product. The synthesizing process, discovered by the German chemist Adolf von Baeyer in 1880, was first applied in the German dye industry in 1897. It opened up a whole new field in the making of synthetic dyes. In this process, aniline is mixed with chloracetic acid to form a product called phenylglycine. Then, the phenylglycine is heated and treated chemically to transform it into a white paste called indoxyl. Indoxyl turns deep blue when air is blown through it. The paste is washed to remove all salt.
Indigo is a vat dye (a dye that is insoluble in water). Indigo paste must be treated with an alkaline reducing agent before it can be used as a dye. The chemical reaction turns the paste yellow and makes a substance that will dissolve in water. After a cotton or woolen fabric has been dyed, it is removed from the vat and exposed to air to oxidize it a deep blue that is resistant to removal by water.
See also Baeyer, Adolf von ; Colonial life in America (Farming) ; Dye ; Pinckney, Eliza Lucas .
