Bronze Plating

Question:

What is bronze, and how does one bronze plate? N. P.

Answer:

Good question! Much to my surprise I find that most individuals in the field of electroplating have no idea what the components are in bronze. Bronze is an alloy consisting of copper and tin. Sometimes other metals are added to improve toughness. Bronze can be plated as a decorative finish and is sometimes used as a substitute for nickel. The color of the deposit can vary from copper color (2–3% tin) to white (> 20% tin). Many different plating baths have been used for plating bronze, with cyanide and pyrophosphate being the most common.

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A typical cyanide plating bath is as follows:

Component Concentration
Sodium stannate 100 g/liter
Sodium cyanide 28 g/liter
Copper cyanide 12 g/liter
Sodium hydroxide 10 g/liter
Sodium cyanide, free 16 g/liter
Sodium hydroxide, free 15 g/liter

Operating Conditions
Temperature 140 – 160 F
Current Density 20 – 50 ASF

A very recent paper discusses decorative bronze plating in detail: N. V. Mandich, Metal Finishing,101, 97-106 (June 2003).