Indigo carmine
Description
A dark bluish purple, synthetic, water-soluble derivative of indigo. Indigo carmine, or Saxon blue, is composed of the sodium sulfonate salt of indigotin. First prepared in 1740 by Johann Christian Barth, a German chemist, it was the earliest synthetic acid dye. Indigo carmine was historically used to color wool, silk and cotton (i.e. denim) from 1770 to the early 20th century even though it was not lightfast and had poor washfastness. Indigo carmine is still used for coloring nylon sutures, food, and drugs. It is also used as a biological stain, a pH indicator and as a detection reagent for nitrates and chlorates. Since 2022, it has been used medicinally to assess urologic and gastrointestinal functions.
Synonyms and Related Terms
Pigment Blue 63 (aluminum salt); Natural Blue 2; Acid Blue 74; CI 73015; sodium indigotin disulfonate; indigo disulphonic acid (Br.); indigocarmim (Port.); indigocarmine; soluble indigo blue; indigotine, Saxon blue; Saxony blue
Risks
- May produce allergic reactions
- ThermoFisher: SDS
Physical and Chemical Properties
- Appearance = dark blue powder that forms blue solution
- Soluble in water. Slightly soluble in ethanol.
- Discolors in acids.
- Changes from blue (at pH 11.5) to yellow (at pH 14.0).
- Composition = C16H10N2O8S2.2Na (mol. wt. = 466.36 g/mol.)
- CAS = 860-22-0
- Melting Point = > 300 C
Resources and Citations
- A.Scharff, 'Synthetic dyestuffs for textiles and their fastness to washing', ICOM-CC Preprints Lyon, Getty Conservation Institute, Los Angeles, 1999
- Colour Index International online at www.colour-index.org Comment: Acid Blue 74; CI 73015
- Helmut Schweppe, Schweppe color collection index and information book Comment: CI 75781 and 73015
- The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 4978
- Wikipedia: