Abstract: A method is described of compacting an anodically produced layer of oxide on parts of aluminum or aluminum alloy. In accordance with the invention, the oxide layer is compacted in two process stages, the parts being pretreated in the first process stage in a solution containing about 6% cobalt fluoride and about 30% nickel fluoride in completely desalinified water at about 30.degree. C. for about 10 minutes and then being treated in a second process stage in completely desalinified water with the addition of a coating inhibitor of about 2 ml/l of triazine derivative at an operating temperature of about 70.degree. C. to the boiling point for about 50 minutes.

Abstract: A method is described for producing colored surfaces on parts of aluminum or aluminum alloy which is characterized by the following process steps:1. The parts are pre-treated by degreasing or cleaning,2. The parts are electrolytically anodically/alkalinely brightened,3. The parts are electrolytically anodized with the use of direct current,4. The parts are electrolytically and/or organically colored, and5. The oxide layer on the parts is compacted.

Abstract: There is described a chemical method for the avoidance of a rainbow effect which is caused by the layer of oxide produced upon the brightening of parts of aluminum or aluminum alloys, in which the parts are degreased or cleaned in a first process step and then subjected to electrolytic-alkaline brightening in a second process step, the method being characterized by the fact that, after the brightening, the parts are subjected to a further treatment in which the parts are first of all washed in water and then exposed in a chromic-acid solution preferably containing about 50 grams per liter of CrO.sub.3 at about 98.degree. C. for about 3 minutes and finally washed again in a sodium hydrosulfite solution.

Abstract: A brightening method for parts of aluminum or aluminum alloy is described which is characterized, in particular, by the fact that the parts are treated in an alkaline electrolyte, operated with direct current, preferably having the composition______________________________________ Na.sub.3 PO.sub.4 (trisodium phosphate) 120 g/l NA.sub.2 CO.sub.3 (disodium carbonate) 330 g/l AlPO.sub.4 (aluminum phosphate) 10 g/l beechwood extracts 5 ml/l ______________________________________at an operating temperature of about 70.degree.-80.degree. C.