Views: 56 Author: Site Editor Publish Time: 2024-08-07 Origin: Site
Indigo is a vat dye and one of the earliest natural dyes used by humans. It is named for its characteristic indigo color.
Indigo is a blue powder that is soluble in hot aniline and almost insoluble in water and ethanol. It is yellow-green in concentrated sulfuric acid and blue precipitate after dilution; it is indigo red in concentrated nitric acid and then turns reddish yellow. It is light yellow in alkaline hydrochloric acid reduction solution and colorless in acidic solution.
Indigo is insoluble in water, acid, and alkali. To make dyeing solution to absorb fabrics, it must first be reduced to become indigo white. Indigo white is soluble in alkali solution and can be used to color animal or plant fibers. After dyeing, it is oxidized in the air and regenerated into indigo, which adheres to the fibers and is blue. Therefore, the indigo dye solution must have a reducing agent and alkali solution.
Indigo is mainly used to dye cotton cloth or cotton yarn. Rural dyeing workshops use fermentation to dye local cloth. Most jeans are made of indigo-dyed warp yarn interwoven with white yarn. Cotton cloth that has not been mercerized is called wool blue cloth. It can be continuously impregnated with hydrosulfite and can also be used to dye wool and silk. It is used in carpets and handicrafts. It is also used to make food dyes and organic pigments. Indigo carmine and bromine indigo are both derivatives of indigo.