Black Nickel Over Brass

Question:

We plate black nickel over small brass components. Quite often the parts come out of the plating bath with a bluish caste to them. The black nickel plating solution that we use contains nickel sulfate, nickel ammonium sulfate, zinc sulfate and sodium thiocyanate. Do you have any suggestions for getting rid of the bluish coloration? K. B.

Answer:

Investigate the thickness of the black nickel coating. If the layer is not thick enough you will tend to get a bluish color on the finished parts. If the color is not consistent over the entire surface, you should also look at your cleaning steps prior to plating.