Method for electrolytically passivating a surface of silver, silver alloy, gold, or gold alloy

A method for electrolytically passivating a surface of silver, silver alloy, gold, or gold alloy, the method comprising the steps of:

• (i) providing a substrate comprising said surface,
• (ii) providing an aqueous passivation solution comprising:
• trivalent chromium ions, and
• one or more than one species of carboxylic acid residue anions,
• (iii) contacting the substrate with said passivation solution and passing an electrical current between the substrate as a cathode and an anode such that a passivation layer is electrolytically deposited onto said surface,
• wherein
• the trivalent chromium ions with respect to all species of carboxylic acid residue anions form a molar ratio in the range from 1:10 to 1:400, and
• wherein the trivalent chromium ions are present in the aqueous passivation solution at a concentration in the range from 0.1 g/L to 5.0 g/L, based on total volume of the passivation solution.