Abstract
The concentration of the residual CrVI and Or111 in the dye‐bath can be decreased to acceptable levels by incorporating a‐hydroxymonocarboxylic acids in afterchrome dyeing using the normal dye to dichromate ratios, the most suitable being lactic acid. The mechanism is based on the reduction ofCrVI to Cr111 which appears to take place predominantly on the wool fibre. The optimum pH range for the treatment is 3.4 to 3.6. Compounds which are substantive to the wool fibre, such as sulphates, or form stable complexes with CrIII such as ethylenediaminetetracetic acid, may increase the amount of the residual chromium in the bath. Other dicarboxylic and hydroxycarboxylic acids, which are also effective in reducing the concentration of the CrVI in the bath, form stable complexes with Cr111, adversely affecting the concentration of the residual Cr111 in the bath.
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