Q. We have an ongoing issue with a steel part that is cadmium-plated and then treated with a chemical conversion coating. After a period of time, black spots start to appear on the surface. What is causing this? –M.C.
A. As mentioned above, there are two probable causes for this problem: inadequate rinsing and a porous cadmium deposit. Your final rinse procedure following the plating step should be alternating cold and warm rinses, ending with a warm rinse.
Check your cyanide concentration and make changes to bring the concentration up to specifications.