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Problems in Rhodium Plating: Black spots, brown spots, blue spots

Q. Hello there !

Are there any additives or brightener solutions and compounds that may be added to prolong the life and improve the rhodium bath solution. My rhodium solution is giving a dark tinge plated surface even though the solution is new and relatively less used (i.e., not many rings of plating of more than 25 seconds have been made, 200 maximum) The bath is a Degussa J2.

Regards,

Pragnesh Zaveri
Jewellery manufacturing - Bombay(Mumbai), Maharashtra, India
2003

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Q. Hi,

I am a manufacturer of gold casting jewellery , where we use J2 Rhodium for plating.The problem I face is that after substantial use of the solution, even when life of solution is not over, the coating seems to be dark. The brightness of the coating decreases with use.

Please also suggest me how to work with Replenisher solutions.

Thank you

Paresh Jain
- Mumbai, Maharashtra, India
2004

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Multiple threads merged: please forgive chronology errors and repetition  🙂

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Q. Hi, I have a problem with Rhodium electroplating. It has some black spots left on the finished products. Please help.

J. Tieu.

PS: I used 2-3.5 Volts @ 30 °C when plating. Where can I get the testing kit for the plating solution? Eg: acid, PH level.

Jack Tieu
Student - Sydney, New South Wale, Australia
2004

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2004

Q. We are currently using Rhodium J1 Solution for electro plating. We have a problem: after plating there are Black spots and yellowish marks.

Plating conditions are --
Anodes: Platinised Titanium
Bath Tank : Plastic
Voltage : 3 - 4 Volts
Current density : 0. 5 - 1 A/ dm2
Time of exposure : 1 min - 2 min for rings.
Bath agitation : 5- 10 cm/s

Bath preparation and other conditions are according to conditions specified by the plating solution manufacture.

Kaushal Pathirana
Plating Shop - Galle, Sri Lanka

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Jeweler getting brown spots in rhodium plating

Q. I am a jeweler who is looking for help with answering a question about rhodium plating. Lately my co-worker and myself have been experiencing a problem with brown spots in our plating on rings. We have tried completely changing the bath, changing the voltage, movement and no movement in the bath, changing anodes and hooks, using platinum anode and hook, platinum anode and white gold hook, platinum anode and copper hook and sterilizing all equipment. We are still (after all this) experiencing trouble. Can anyone please shed some light for us. I'm getting pretty frustrated and am at the end of my rope.

Stacy Jones
jeweler - Greenfield, Indiana, United States
2004

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A. Except in extremely clean conditions and then only with very special proprietary electrolytes, all rhodium is deposited with cracks. Copper and Silver migrate right through the cracks and show up as brown (copper) or gray to black (silver). Put nickel under the rhodium as a diffusion barrier. Robert H Probert Robert H Probert Technical Services Garner, North Carolina 2004 A. This problem happened to me also until I put the ring into a cleaning concentrate called TIVACLEAN by Krohn. I hope this information will help you. David Zobali jeweler - New City, New York 2004

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Multiple threads merged: please forgive chronology errors and repetition  🙂

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Help! rhodium plating troubleshooting!

2005

Why my platinum anode and platinum plating wire which being used to hang the item are always having a black spot after I plated several items?
My cleaning process:
-after polishing, I use ultrasonic machine
-boil the item
-electrocleaning using 35 grams tri-sodium phosphate solutions for 1 minute
-rinse in water
-dip in 10% sulfuric acids for 1 minute
-rinse in distilled water
-dry the items
-ready to plated

Condition of the rhodium plating:
-100 Fahrenheit
-3 volt
-anodes:platinized-platinum (mesh)
-cathode:platinum or 18K

Please help me.
thank's

Hendy adisaputra
Pantes - Cirebon, Indonesia

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Hello Hendy,
You did not mention that you had any problems with the plated part, which is the most important thing. It would be a good idea to have the solution checked for metallic impurities. Sounds like the unwanted metal present in the bath is oxidizing. Do you have adequate solution agitation? A filter pump is worth it's weight in gold, and you can carbon polish the bath periodically using carbon filter tubes, which would keep organic contamination down. Your rhodium supplier should have a procedure for precipitating metallic impurities so you can purify the bath yourself if need be. Let me know how you make out.

Mark Baker
process engineer - Malone, New York
2005

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Q. Hello,

We are a small jewelry company which has been experiencing very frustrating rhodium issues lately. We have been getting black spotting all over our pieces when we go to rhodium. We have tried replacing everything in the process from the anode, to the acid to the electrocleaner to the rhodium to the metal clips ... nothing helps. We tried variable dipping times, temps, and voltages ... no help. We need any assistance to this issue and can supply pics if needed. Thanks!

Ramy Mawad
jewelry - Los Angeles, California
2006

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A. Ramy, You mentioned you have changed everything including the rhodium bath, correct? If the black spots appear right away after changing the rhodium bath I would have to say the problem probably lies in the pre-clean process. You may have polishing compounds that are not being removed in cleaning. Are you using a hot soak clean followed by heated ultrasonic cleaning? These process steps loosen up the compounds, then can be blasted off by your electrocleaner. A 10% Sulfuric dip and DI water rinse should also be used before going into the rhodium. For the rhodium bath you should be using a white polypro tank with platinum clad anodes. Stainless steel rods are fine for buss bars. What is the size of the Rh tank? If it is 3 gallons or more a small filter system would help keep the solution clean, and give you some solution agitation. Hope this helps, and good luck! Mark Baker Process Engineer - Syracuse, New York 2006 2006 A. Rhodium process is very acidic and plating efficiency is very low. During plating, lots of hydrogen gas generate on cathode. Your problem could be gas bubbles attach on jewel surface and cause pitting. Improve solution movement or add in small amount of wetting agent may help. David Shiu - Singapore A. Rhodium over what? If over silver, then the silver is migrating through the cracks in the highly stressed rhodium and galvanically corroding on top. Robert H Probert Robert H Probert Technical Services Garner, North Carolina 2006

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Q. Thank you to all who responded here. Let me clarify my situation in more detail now as I should have done in the first place. We make jewelry pieces at our shop in 18 kw / palladium.

We have a plating section set up in our shop to plate rings one at a time. The Rectifier is a 30 amp with brand new alligator clips. 600 ml Pyrex beaker [beakers on eBay or Amazon [affil links] s for all our solutions. Stainless steel anode which has been cut in length a little to fit one beaker for the KROHN Heavy duty electro solution. 1 gram of rhodium solution (acid based) in another pyrex beaker with a platinized titanium anode. Clean Earth Dry Acid Salt solution in another beaker for surface preparation between the electro-clean stage and the rhodium stage. Between each stage after the electro-clean there is a beaker filled with Distilled water to rinse off the piece.We also have tried air-can drying the piece between the last dip in distilled water and the final rhodium plating stage.

We have tried every conceivable procedure including buying the anodes, clips, rhodium and electro-clean solutions one time over to ensure there was no contamination problem. We have tried varying volts (1-3 volts ) and times (10-25 seconds) making sure not to burn the rhodium in the process and used heating plates at the recommended temperatures for both the rhodium solution and the electro cleaner alternatively.We have plated the piece over as well with the results too negligible to make a difference. Also we make a thorough ultrasonic cleaning before hand and steam the piece properly before attempting to plate , using a white gold hook on the alligator clip to make the transfer over to the plating section. We never handle the piece by hand after the steaming process until the piece has completed the plating process.All beakers have a rubber stopper that fits airtight to protect from evaporation and contamination.

Thinking it could be our type of alloy in our gold (palladium), we tried using other mixtures of alloyed golds... the same result always ensued. An evenly distributed pattern of tiny brown/black spots over the entire piece. It is hard to see in certain types of lighting but under some lighting it becomes quite apparent. Almost like a leopard pattern I'd say.

Ramy Mawad [returning]
- Los Angeles, California
2006

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A. Hi Ramy, Thank you for clarification on your process. I assume you are starting out with Au - Pd alloy castings? If I am correct, it is very possible you have micro pores in the casting that are being magnified after your Rh "flash". The best way I know to verify this problem is to take a ring off the line just before the Rh process, rinse, dry and examine under magnification. If you do see small pores in the casting, polishing has to be improved. When you stated you had a 1 gram Rh solution, do you mean 1 gram Rh metal per 600 ml of plating solution? That seems a little low to me. Most Rh solutions I have worked with contain 10 grams Rh per gallon. In beaker plating you can break that down to 1 gram Rh metal for every 378 ml of solution. The lower the Rh metal concentration in the solution, the higher the hydrogen evolvement will be, lower plating and distribution thicknesses will also be a factor. It would benefit you to increase the Rh concentration to 2.65 g/l. Good luck and let me know how you make out. Mark Baker Process Engineer - Syracuse, New York 2006 A. I would suggest that you replace the rhodium solution with another product completely. Next if you are steam cleaning the jewelry before plating, stop this practice, you are introducing contaminants if it is hooked to the city water supply. If you are using it, consider eliminating red rouge from your polishing operation as this is a "iron" contaminant and yes it is everywhere unless you are plating in a 100x clean room with separate filtered air intake. If all else fails and you think it is the white gold alloy itself, consider using a yellow gold strike first prior to the rhodium plating. This will also help keep the rhodium bath cleaner much longer. By the way you should be using a heated magnetic stirrer to prevent local overheating of the rhodium chemistry. Good luck, David Vinson Metal Arts Specialties - Leonard, Michigan 2006

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