A red coloring medium made from phenol or carbolic acid. It is soluble in alcohol and ether but insoluble in water. When fabrics were steeped in this solution, the color was nonactinic and therefore safe for darkrooms, windows, and doorways. Aurin was also mixed with water-soluble gums and brushed on the backs of collodion and silver bromide gelatin plates as an antihalation layer.
It is soluble in strong acids to form yellow solution, or in aqueous alkalis to form carmine red solutions.
Aurin, sometimes named rosolic acid or corallin is an organic compound, forming yellowish or deep-red crystals with greenish metallic luster. It is practically insoluble in water, freely soluble in alcohol.
Due to this behaviour it can be used as pH indicator with pH transition range 5.0 - 6.8. It is used as an intermediate in manufacturing of dyes.
