It sounds like the process of plating steel. I've done a little electric work in a few plating companys. Some of their parts where black when finished. I'm not sure what the plating material was. Cadium I think. I know this process does add thichness to the part, but I don't think warping was an issue. It was a very caustic process. My hand tools would rust by the end of the day just working in the plant.