Copper in Silver Plating Tank
Recently the silver deposits have developed a dark appearance. All of our plating bath numbers are in line with the chemical vendor’s recommendations. Do you have any suggestions on how to solve this problem?
Q. Our company does a lot of silver plating using cyanide plating baths. Recently the silver deposits have developed a dark appearance. All of our plating bath numbers are in line with the chemical vendor’s recommendations. Do you have any suggestions on how to solve this
problem? T.D.
A. Excess copper in the plating bath is probably the most likely cause of your problem. A concentration of 0.8–1.0 oz/gal of copper will cause this dark deposit. Your can dummy the bath to remove some of the copper. A current density of 4–5 asf should be used. Corrugated iron will work well as the dummy. Be aware as you will also plate out some silver in the process.
A longer term solution is to try to prevent copper from entering the plating bath in the first place. Is the copper being dragged in from a prior plating step or are you plating silver on a copper or copper alloy base material?
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