One of my customers is covering the plating on some small electronic connectors with a black oxide coating. This is the specific plating process that they are using: Caswell Inc. - Black Oxide Kit

The problem is that our parts are already pre-plated with a shiny nickel finish over brass. The customer is finding that the black oxide plating is not adhering well over the nickel plated surface.

Drawing on my car and homeowner experience, my feeling is that the customer will have to break the finish before applying the black oxide. In the past, I've used Duplicolor Self Etching Primer on some of the metal parts I've painted. For my customer's project, I would think something similar might work. The parts would probably have to be dipped, so a canned liquid might be better - there will be hundreds of small parts, so sanding isn't an option.

Any suggestions?

Thanks,
Al