Studies on Mixture Dyeing. III. The Absorption Spectra of Direct Dye Mixtures in an Aqueous Solution

The absorption spectra of a binary mixture of five representative direct dyes in solution have been investigated. The equilibrium constants for complex formation are in the 107–104 range and are in the order: Chrysophenine G - Sky Blue 6B>Benzopurpurine 4B - Sky Blue 6B>Sirius Red 4B - Sirius Supra Blue BRR>Sirius Red 4B - Sky Blue 6B= Benzopurpurine 4B - Sirius Supra Blue BRR>Chrysophenine G - Sirius Supra Blue BRR. The combination of Chrysophenine G and Sky Blue 6B is a typical one in direct dyes. The equilibrium constant for an aggregation of like dye molecules is very much smaller than the value of 104 at room temperature.