(Post-treatment) process for various metals in which the workpieces are usually treated currentlessly, less frequently electrolytically with solutions containing hexavalent chromium, among other things. Chromating-phosphating-mixing processes were common, especially for aluminium. Chromating produces transparent, glossy, blue, yellow, olive and black cover layers by dipping, brushing or spraying, rarely green or grey. They serve to improve tarnish and corrosion protection and paint adhesion.