An electrocoagulation printing method comprises the steps of (a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, the passivated surface defining a positive electrode active surface; (b) coating the positive electrode active surface with an olefinic substance and silica to form on the surface micro-droplets of olefinic substance containing the silica; (c) forming on the olefin and silica-coated positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing the electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and (d) bringing a substrate into contact with the olefin and silica-coated positive electrode active surface to cause transfer of the dots of colored, coagulated colloid from the surface onto the substrate and thereby imprint the substrate with the image. The use in step (b) of silica prevents abrasion and pitting of the positive electrode, without substantially affecting passivation. The use of silica also prevents the formation of undesirable background on the printed image in step (d).
