Patent ID: 8268096

Claim:
A process for producing colored layers on surfaces of zinc, aluminum, magnesium or alloys thereof, comprising contacting a metal surface of zinc aluminum, magnesium or an alloy thereof with a chromium-free aqueous treatment solution consisting essentially of a total of 3 to 35 g/l persulfate ions and/or peroxodisulfate ions and no more than 10 g/l ammonia or ammonium ions, for a time of 0.5 to 5 minutes sufficient to thereby produce a colored layer on said metal surface, wherein the aqueous treatment solution has a pH of 10 to 12, a temperature of 30 to 70° C., and additionally contains 1 to 50 g/l sulfate ions, wherein the treatment solution contains no metal ions other than alkali metal and optionally alkaline earth metal ions.