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Is Congo Red vegan?

Congo Red is a synthetic azo dye and the sodium salt of 3,3′-([1,1′-biphenyl]-4,4′-diyl)bis(4-aminonaphthalene-1-sulfonic acid). It is water-soluble, yielding a red colloidal solution, and was formerly used in the textile industry but has been largely abandoned due to its carcinogenic properties. It is still used as a histological stain and as a pH indicator.

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