Abstract: A process for electrolytically forming on a metallic element a protective layer or film in an electrolyte consisting of an aqueous solution of preferably sodium silicate or alternately of other salts rendering the electrolyte substantially basic, the metallic element constituting the anode in the process. The processed metallic element has particular usefulness as a support member for photolithographic printing plate, the electrolytically formed film acting as a barrier layer preventing deterioration of the light sensitive diazo resin, or the like, utilized as a photosensitive coating on lithographic plates.