Direct cathodic reduction of oxidised CI Sulphur Black 1 was achieved by means of a multi-cathode electrolyser at cell currents of 0.9-1.5 A. The redox potential in the catholyte decreased from initially -250 to -533 mV as a function of charge flow. The catholyte also served as dyebath for cotton fabric samples. Colour depth was characterised by Kubelka-Munk value K/S and CIELab-coordinates and was studied as function of charge flow and redox potential in the catholyte. Direct correlation between redox potential and colour depth of the dyed samples was observed. Electrochemical reduction permits steering of catholyte/dyebath potential by adjustment of cell current and thus permits direct control of the dyeing process by electrochemical methods.