Producing a coloured oxide on an article of aluminium or aluminium alloy

Abstract From the Canadian patent

A method of producing a colored oxide coating on aluminum or aluminum alloy includes first forming an oxide coating on the aluminum or aluminum alloy by anodic oxidation. The coated aluminum or aluminum alloy is then arranged to form a first of a pair of electrodes in an electrolytic bath containing metal ions, and first and second voltages are alternately applied across the electrodes to produce first and second direct currents respectively flowing in opposite directions, with the voltage across the electrodes when the first electrode is cathodic being sufficiently large to cause electrolytic deposition of the metal ions on the oxide coating thereby coloring the coating.