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Black Zinc Plate

Recently one of our plating baths started to give a black finish instead of the clear finish after the chromate conversion coating. What’s going on?
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Q. We do a lot of bright zinc chloride plating. Recently one of our plating baths started to give a black finish instead of the clear finish after the chromate conversion coating. What’s going on? B. U.

 

A. Your e-mail did not give me much in the way of information but I suspect that the cause of your problem is the zinc plating bath has been contaminated with copper, cadmium, or iron.

The first thing to do is perform an analysis of the plating bath. You should pay particular attention to the copper, cadmium and iron concentrations.

The second thing you should do is dummy the plating solution to remove the impurity heavy
metals.

Finally, you should institute a testing program that tests plating baths, as well as all your other process baths, on a regular scheduled basis. 

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