PROCESS AND ELECTROLYTE FOR THE SELF-COLOURED ANODISATION OF ALUMINIUM AND ITS ALLOYS

1,213,114. Colour anodizing aluminium. COMPAGNIE PECHINEY. Feb. 7, 1969 [Feb.9, 1968], No.6765/69, Heading C7B. An aqueous electrolyte for self-colour anodizing aluminium or alloys thereof (e.g. containing Si, Mg and Mn) comprises, e.g. in deionized water, 10-300 g/l sulphomaleic acid and an amount not exceeding 15 g/l sulphuric acid. A light bronze to black coloured alumina layer 10-50 microns thick may be formed using direct and/or alternating current of density 0À5-10 amp/sq dm. Prior to anodizing, the aluminium (alloy) may be (electro) chemically pickled first in NaOH then HNO3 solution to produce a matt surface, or mechanically or electrolytically polished to produce a shiny surface. The alumina layer may be sealed in a boiling solution of 0À5-2 g/l nickel acetate.