Abstract
An attempt has been made to reduce the dyeing time with afterchrome dyes by eliminating the cooling step before afterchroming. This cooling is normally necessary to control the rate of chroming to obtain level dyeings. Other methods of control have been investigated, including the use of chromium fluoride rather than potassium dichromate. Triphenylmethane dyes containing salicylic acid groups can be chromed with chromium(III) at the boil, giving a brighter dyeing and a lower rate of chroming than when dichromate is employed. Salicylic acid azo and some oo′‐dihydroxyazo dyes can also be chromed with chromium(III) compounds, but the colours produced differ greatly from those obtained when dichromate is used. With other afterchrome dyes, such as oo′‐dihydroxyazo dyes, that have additional substituted or unsubstituted hydroxy] or amino groups capable of interaction with dichromate, the mechanisms of chroming with chromium(III) and chromium(VI) are different.
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