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



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An ongoing discussion beginning back in 2004 ...

2004

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

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
^


Rhodium Plating Solution


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2004

A. Black spots in plating are usually caused by contaminants in the plating solution, often tramp metals. The supplier of the rhodium plating solution should be able to provide guidance though.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


2004

A. Dear Kaushal

Improve your pretreatment and switch to j-2 in place of j-1 because in j-1 there is no wetting agent it is for barrel plating and in vat due to lack of proper agitation it gives black spot.

Thanks,

Qutub Saify
- Ajman, UAE
^



Jeweler getting brown spots in rhodium plating

2004

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
^


simultaneous 2004

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 probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
^


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
^



We merged some threads on this page. Please forgive what may look like disrespect of earlier responses; they weren't here :-)



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% sulphuric 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
^


2005

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
^



2006

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
^


simultaneous 2006

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

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
David Shiu
- Singapore
^


2006

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 probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
^


2006

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 beakers 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
^


simultaneous 2006

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

A. I think your rectifier is too much, even at 1.0 volt you are drawing too much current( a lot of gassing) for one ring. Get yourself a 0-10 amp meter with .2 amp graduations.
connect to the cathode side. Start with 1.0 amp,3.0 sec. ,rhodium solution at room temperature. moving the ring back and forth for agitation( not too fast it is jumping off the hook.Check your piece for coverage, increase current or time as needed. If problem persist cut back on current. Check pieces for coverage, increase time as needed.
Make sure to electroclean(cathodic -),rinse, hot pickle, rinse, Plate.

Emery out old rhodium plate before polish.

Good luck.

Hamilton Solidum
- Mays Landing, New Jersey
^


2006

A. I get black spot problem if I have not melt properly.

Black spot problem I get in Ni base alloy white gold rings but I solve that problem by nickel plating and then Rh plating.

Rh should be at least 2 g per liter and plating time should be 120 seconds at least.

Dipen Pattni
Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania
^


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2006

A. Dipen,
I'm sure you have heard of the high percentage of people that are allergic to nickel in this world. Covering a white gold alloy with a nickel plate then rhodium to hide "black spots" is a practice that should not be tolerated in the jewelry industry, especially in fine gold jewelry! What will you have when the rhodium wears down? Nickel plated white gold! I don't know anyone that would be pleased to buy or wear that finish.

Mark Baker
Process Engineer - Syracuse, New York
^


2006

A. Hi,

Yes, there is high percentage of people that are allergic to nickel, I get this problem in very few cases, of course I also tell to customer about same.

Some times we have very short time to delivery jewellery and problem comes out then only solution is left.

Also using high percentage Ni base alloy in gold which will also make problem to skin.

Another solution is to do Ni free plating.

Dipen Pattni
Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania
^


2006

A. Hi Ramy

I suggest you verify the porosity and if its actually porous cast material, I would suggest you Plate a WHITE BRONZE bright layer first.

That's NON allergic.

Then Plate with Rhodium . The Bath should use Platinised Ti anodes and you must move the component around between the anodes to build up a solution flow past the piece.

Or use a Magnetically stirred heater.

This is how lots of people deal with Porous castings.

asif_nurie
Asif Nurie [dec.]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016

^


2006

A. One thing that stands out is that you said you are using a stainless steel anode. This may be causing the problem. You should be using a platinum or platinized titanium anode for rhodium plating. Double check your anode material.

Good luck,

Jim Sivertsen
Refining & Alloys - Alden, New York
^


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