Method and apparatus for reducing vat and sulfur dyes

The invention relates to a method for the electrochemical reduction of vat and sulfur dyes in aqueous solutions, in steady-state conditions of reaction and a cycle which is largely free of reducing agents. The invention also relates to apparatus for carrying out said method. The steady-state conditions of reaction are obtained by means of a start reaction. The substances used for this reaction and the products resulting therefrom are extracted from the cycle. To maintain the cycle only dyes, an alkali and possibly small quantities of additional substances, such as surface-active agents, need to be added. No other chemicals active in the oxidation-reduction process are used.