Gray/Black Spots on Nickel

Question:

We recently received some hardware that was manufactured in Italy. They turned out to be copper that had been plated with nickel. There was some pitting that showed through. After a few months in storage, they turned gray and black. The amount of discoloration varied with each piece. Do you have any ideas what may be causing this and is there any simple way to clean it? A mild soap and Scotch Brite pad seems to remove most of it, but it also takes off some of the nickel plating, which is very thin. T. G.

Answer:

Since the specifics of the nickel plating process are unknown, it would be mostly conjecture trying to determine what the problem is. Your e-mail states that the nickel plate is very thin and this is probably the cause of this problem. The nickel plate (I am assuming that it is bright nickel deposit) is not heavy enough and probably contains a fair number of pores. This porosity offers a corrosion pathway. The best way to resolve this is to require your vendor to apply a heavier nickel plate. A semi-bright deposit should be applied followed by a bright deposit. Pitting can also be caused by poor preparation of the copper substrate.

Removing the gray/black spots most likely will not be a solution since they most likely will reform.

Are you sure the gray/black areas were not present when you first received the parts? If a nickel plating bath has zinc, copper, lead or iron present in appreciable concentrations these kinds of spots will appear.