Nickel Plate Staining

Q. We electroplate nickel over brass. In the process, we use a soak cleaner, ultrasonic cleaner and anodic sulfuric acid/nitric acid cleaner. Parts are bright dipped in a sulfuric/nitric/chromic acid bright dip. We also have used a bright dip in dilute hydrochloric acid and 10 percent sulfuric acid. The parts are plated for 8-10 minutes in a Watts nickel bath. All of the parts come out stained. Can you make some suggestions on how we can overcome this problem? —T.R.
 

A. As a starter I must ask for a more detailed description of your process. The details are important when trying to solve a problem— factors like temperatures, process steps and deposit thicknesses. Based on your e-mail I was unable to determine whether cleaning methods used were in sequence or as separate experiments. But there are some suggestions I can make that are general in nature. Stained or spotty deposits can be due to poor cleaning, uneven temperatures and decomposed organic additives. Since you are using a bright nickel bath, the last possibility is probably the most likely.

If you are performing all of the cleaning processing steps in sequence, then I would blame overcleaning. Just like under cleaning will cause problems, excess cleaning will also cause problems. Something else to consider is the thickness of your nickel deposit. Deposits that are too thin are porous and may cause the absorption of your plating solution that in turn will cause spotting.

I’m sending you a copy of the Nickel Tank Doctor. It contains information on troubleshooting of Watts and bright nickel plating baths.