Rhodium Plating Problems

A. Since the hard to clean areas are plating bright and these are probably also low current density areas I believe you either have your current too high or you are not agitating your part enough or both. In plater's lingo you are "burning" the part.

A. Hi Eric. Are you plating onto white gold, silver, a nickel underlayer or what? Please introduce yourself and your situation as we don't know if you are a beginner working with your first bowl of rhodium plating solution, or a process engineer with decades of experience running an industrial plating operation.

If you are new to this, my first suspicion would simply be that you've run out of rhodium. There is only 1 gram of rhodium in a typical half liter of solution. The anodes are not the source of the rhodium, they are platinized titanium insoluble anodes. Good luck.

Regards,

Q. Rhodium plating. Golds and platinum. In the past 4 months this has been happening. Solution turning black, but still works.

Constants: same rhodium solution supplier for over ten years
Same anode for about 3 years.
Same users
Same connectors
Same temperature
Same voltage and current
Same time limit on dipping.

Previous baths gave gotten weaker through high usage but it begins to lose the color not turning black as it does now. Could the supplier have changed the chemical makeup of their solution? Us the platinum titanium anode bad? Thank you for your help Ted

A. Hi. Thanks for the graphic. Now I see that I misread your inquiry and you meant the solution itself is turning black. Hopefully someone else will have a clue. That pitcher is glass, not plastic? And it's what you always store it in?

Regards,

A. Platinum plating baths will start out yellow and turn black. We believed the platinum ions are reduced in solution as another species is oxidized. The solution turns black as solid platinum metal colloids are formed.

I have limited experience with rhodium plating solutions and I would think a similar model is possible. The bath stability would depend on the choice of complexing agent (sulfamate or something else) and possibly the pH.

If the bath could be analyzed for rhodium concentration, pH, other metal ion impurities, and other components (if possible) this might help shed some light on the likely cause.

Hope this helps.

Rhodium solution turning black: it was the anode in the solution. It was old. I told them to check all of that stuff. Your answers to my questions helped Very much. Thank you very much. Now I have some diamonds to set!