1,133,461. Electro-plating with a film of chromium and chromium oxides. CORILLIUM CORP. Dec. 9, 1965 [Dec.31, 1964], No. 52297/65. Heading C7B. A lustrous black corrosion resistant adherent film of Cr and chromium oxides is electro-plated on a conductive base as cathode using an electrolyte which comprises in aqueous solution at least 65% by weight of an admixture of 30 to 80% by weight of chromic anhydride and 20 to 70% by weight of a non-substituted lower aliphatic acid, maintaining the electrolyte at 50‹ to 85‹ F, and employing a cathode current density of from 25 to 1000 amps/sq. ft. The lower aliphatic acid is a carboxylic acid containing an aliphatic carbon chain which contains no substituents and comprises from 1 to 4 carbon atoms, e.g. acetic, propionic butyric or valeric acid. The solution may also contain barium acetate. Anodes may be of carburized steel, stainless steel, carbon or lead. The anode surface area should be at least as great as and may be three or four times as great as the cathode surface area. The electrolysis tank may be lined with polyvinyl chloride. The exterior surface of an article may be rendered matte prior to the electro-plating. After making up the electrolyte solution from its constituents, the solution may be conditioned electrolytically prior to the electro-plating. The plating bath may be replenished as constituents are consumed. Trivalent chromium may be electrolytically converted to its original hexavalent form.