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Discoloration on Rhodium Plate

I haven’t found an answer to this problem. Our company manufactures laser engraved keepsakes in various metals. Most common is sterling silver, which we Rhodium plate. We also Rhodium plate white gold and brass display pieces. I’m trying to troubleshoot results. On occasion, one of the Jewelers will have pieces with milky areas after the final Rhodium bath. The other problem is brown stains after the final plating. I’m pretty sure the brown stains are caused by insufficient rinsing between baths.

Our usual process for precious metals is Electrocleaner>Rinse>Palladium>Rinse>Rhodium. Brass display pieces include an Acid Dip after Electrocleaner. We work at room temperature and plate up to a dozen pieces at a time.

The process was developed by Jewelers before me. I’m trying to get an acid bath and distilled water instead of filtered water added to all plating runs. The milky discoloration is not usual, the brown stains more often, but not usually.

Any thoughts or explanations?

Ruth Annie
I am by no means an expert but have been doing my own plating for 35 years and rhodium can be tricky. I always use distilled water for all solutions and rinses. I never reuse wires wire that connect piece to rectifier. I always heat solutions to manufacturers specs. Finally about every 50 plating or so I start with all fresh solutions Also use a product from Rio Grande called Midas carbon treatment for rhodium. It removes organic contamination in liter batches.
Hope this helps

Thanks Franz. We are now using distilled rinse baths for everything. This has helped. I made stainless steel racks for pieces. We are a production operation so it’s not feasible to wire pieces individually or with fresh wire every time. We plate 12 pieces at a time, 20+ runs per day (about 80cm2 per run). We can get close to 200 runs from a batch of Rhodium before the color on the finished piece starts to shift. Our management has nixed the carbon treatment for now. I’m trying to get them to OK replenishing solutions. We use Legor Ultrabright that we get from Rio, which is rated OK to use at room temperature, which we do, and plate sterling and white gold with a Palladium under-plate before the Rhodium bath. Our Rhodium is 90 seconds at 3V. That’s the maximum I can get before burning or other problems crop up. Our executives have mandated this longer time since we had customers wearing the plating off of their pieces. Our products are keepsakes with engraved fingerprints of deceased loved ones. They get handled far more than conventional jewelry. We’ve had customers wear the fingerprint off of silver pieces in 3 years!

I continue to learn and research and figure things out. We are getting it under control.

Ruthanne Robertson