Q. We have received a request to apply black oxide to a part that also requires cadmium plating. The parts have already been cadmium plated. Is it possible to put black oxide over cadmium plate? Will the cadmium plate be degraded by the black oxide solution? Will the black oxide solution be degraded by exposure to cadmium? P.G.
A. This is an interesting series of questions. As you might guess, this is a nice way of saying I really don’t have answers to your questions! As I understand it, the parts are already cadmium plated and certain areas must have a black oxide finish applied. It is not clear from your e-mail whether the parts required the black oxide for corrosion protection or a decorative finish only. Nor do you state whether your customer requires a “classical” black oxide solution, which typically is applied at high temperature. I am not aware of any masking materials that will stand up to the temperatures of a black oxide solution. There are materials available that will give you a black finish essentially at room temperature or above, but the finish does not give you the same amount of corrosion protection as the classical black oxide finish.
Since I do not have answers to your questions, I am asking my readers to comment. If you have suggestions as to how this problem might be solved, I would appreciate hearing from you.