Color Variation in Brass Plating

Q. How can we avoid color variations in brass plating?­—K.H.

A. The best way to minimize color variations is to have good chemical control of your plating bath. You do not mention in your e-mail the exact type of brass plating bath you are using, but a typical bath will apply a 60/40 copper/zinc alloy. The classic bath is a cyanide-based bath. The key factor in any type of bath is the ratio of copper to zinc in it. The more zinc deposited, the whiter the brass deposit; more copper gives you a redder deposit.

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The current density and temperature also influence the appearance of the deposit. High current densities tend to raise the zinc content of the deposit, while higher temperatures tend to lower the zinc content. Pay close attention to the temperature of the bath; temperature variations do affect brass colors. pH also plays a role in the appearance of the brass deposit.

Experienced brass platers also know that a reddish color to the deposit can be due either too high a copper content or a very high zinc level. In both of these cases, steps must be taken to either reduce the amount of copper in the plating bath or to lower the pH, which also lowers the amount of zinc content.

As you can see there is no “silver bullet” in controlling a brass plating bath.