DYEING BEHAVIOR OF INDIGO REDUCED BY INDIRECT ELECTROLYSIS

Dispersed indigo dyestuff can be reduced by indirect electrolysis usin g an iron(II)triethanolamine complex. The iron (III) form of the compl ex can be transformed to the iron (II) form by cathodic reduction, thu s leading to a regenerable reducing agent. Electrochemically reduced i ndigo is tested in laboratory scale dyeing experiments, and the result s of different reduction conditions in the dyebath are discussed. The influence of the concentration of the complex-system on the build-up o f color depth and shade with increasing number of dips is discussed an d compared with samples of the standard dyeing procedure using sodium dithionite as reducing agent. The results of the latter conventional p rocess shown that the dyestuff in the dyebath behaves in a manner simi lar to that when a regenerable Fe(II)-complex is used as the reducing agent.