Patent ID: 8211285

Claim:
An electrolyte, for the deposition of a decorative bronze alloy layer which is optically defect-free and has an anthracite grey to black color on a substrate, which comprises water-soluble salts of copper, tin and zinc which form the decorative bronze alloy layer and phosphonic acids consisting of aminotris(methylenephosphonic acid) and ethylene-diaminetetra(methylenephosphonic acid), wherein said electrolyte is free of cyanides, additional phosphonic acids, thiourea derivatives and thiol derivatives and wherein the copper, tin and zinc are in an ionically dissolved form and the ionic concentration of copper is in the range from 0.2 to 5 gram per liter of electrolyte, the ionic concentration of tin is in the range from 0.5 to 20 gram per liter of electrolyte, and the ionic concentration of zinc is in the range from up to 5 gram per liter of electrolyte.