Colored, anodized aluminum-base article and method of preparing same

Claim 1

A colored, anodized aluminum-base article comprising: an aluminum-base substrate selected from the group consisting of aluminum and aluminum alloys; a corrosion and weather-resistant inner aluminum oxide film formed on the surface of said substrate and having a thickness of between 30 and 150 microns and a Vicker's hardness number of at least about 330 Hv said inner film being uncolorable and having a metallic appearance; and an outer transparent and porous aluminum oxide film provided over the surface of said inner film and having a thickness of between 5 and 25 microns, a Vicker's hardness number of not greater than 270 Hv and a pore size between about 200 and 300 A; a coloring agent deposited in a substantial portion of said pores by immersion in a coloring solution, said coloring agent imparting color to said article without destroying the transparent quality of said outer film; said outer film having been formed by anodizing said substrate in a first electrolyte bath said bath consisting of a sulfuric acid solution using graphite as a counter-electrode at a controlled temperature between 20 and 40° C. at a constant direct current density; said inner film having been formed under the outer film by anodizing said substrate in a second electrolyte bath, said second bath consisting of a sulfuric acid solution using graphite as a counter electrode at a controlled temperature not higher than 10° C.; said article having a deep metallic color by the combined effect of the color of said transparent outer film and the metallic appearance of said inner film showing through the transparent outer film.