Our shop does rhodium plating and recently we have run into a problem when plating rhodium over small flat washer-like copper disks. The parts are first cleaned and then gold-flashed with 8–10 microinches of gold. The rhodium is than applied over the gold flash. We apply 25–35 microinches of rhodium. The parts blister around the edges and many are streaked. What are we doing wrong? F. T.
The streaks are probably the best clue to what is wrong here. I suspect that you do not have a heavy enough gold layer on the parts. I would increase the thickness of the gold flash. An alternative is to replace the gold flash with a heavier nickel strike.