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topic 42108

Rhodium Spotting Problems

(2004)

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

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., Southern, Sri Lanka


Rhodium Plating Solution

(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 Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


(2004)

A. Dear Kaushal

Improve your pretreatment and switch on 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



Rhodium Plating System

(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

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como


(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 M. 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


sidebar (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
- 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



(2007)

Q. Hi there all ,

Well I'm extremely interested in this problem as we are having the same issues . We recently built a small plating room in our factory ( small 35 - 40 person) we purchased an all in one machine 3 liter from Italy but picked it up in their office in Bangkok . The Rhodium is 2 grams per liter. Right from the start we have worked to follow the letter of the law as best we could gather with little plating experience . we are using DI throughout Ultrasonic with cleaner , DI, Degreasing with Anode cathode 30 seconds at 4 volts stainless anodes (2) DI again then again then Sulfuric acid 5% per liter ( I see some suggest 10% - will try ) then DI , Rhodium , recovery and DI again using final DI to top up recovery and recover to top up Rhodium bath .. we started out with problems as the machine arrived wired backwards - once we trouble shooted that seeing our first sample turn to well ... looked like casting again ..once we figured it out the supplier / manufacturer omitted the possible de-plating of Anodes ( platinized titanium ) well after rewiring sample came out pretty good but two days later our anodes de-plated in the bath - so we had to filter ( paper filter ) everything and replace the anodes - we are now having spotting and inconsistent results - we just don't have it down - the room is a little hospital we are trying to get it right but don't have it - someone mentioned heat soak before ultrasonic - just hot DI ? over an element in a beaker ? and 10% Sulfuric per liter ? Also we sent our goods to a local plater to nickel first so we could rhodium ourselves but the nickel went sour with small bumps showing up - so we are trying to set that up as well . Someone suggested palladium plating first to cut rhodium use and avoid nickel - ideas . anything would be helpful ..Robert - in paradise but suffering !

Robert Duffield
Jewelry Factory - Denpasar, Bali, Indonesia

Ed. note: We deleted the names of the suppliers, Robert, because it really wouldn't be fair to them to post public criticism. Good luck.


(2007)

A. Here's my two bits worth on Rhodium Plating.
I have 20+ years in a jewelry shop environment. Right now a retail store in 4000 pop. town. I do it all. Here's a list of what I use to get bright white rhodium.

1. Best polish you can get (I use green rouge).
2. Ultrasonic cleaning (using some yellow stuff called supersoap right now).
3. Steam clean (tap water, distilled good if you have bad city water).
4. Electro-clean solution 35 seconds, gold hook (8 teaspoons Earth-Clean in a pint of tap water, stainless container).
5. Rinse in Distilled water ( used multiple times ).
6. Half pint premixed Rhodium in glass jar, room temp. 6 volt lantern battery (big square one with two connections on top) first dip 20 sec, second 15 then 10.
7. Tap water rinse.

I mask off using finger-nail polish when needed.
Canned air to dry-off first.
Must add water if heating rhodium to keep strength right. Watch the color, too strong can spot rings.

I might just be lucky but that's my story.

Tim Stodola
- Pilot Point, Texas



July 11, 2008

Q. I am a goldsmith with limited knowledge of Rhodium plating. A common issue has come up for myself and another jeweler that I work with is that we are getting black spots on the pieces after we plate them. We are cleaning the pieces in the ultrasonic and steaming them afterword. We then put them into the rhodium bath at 4.5 volts for 10 to 15 seconds. It doesn't happen all of the time but when it does it is a real nuisance. Do you have any suggestions as to what might be causing this and we might minimize this problem.
Thanks,
Kate

Kate Short
Goldsmith - Oakland, California



February 15, 2009

Q. Hi. Two weeks ago we moved our rhodium bath from one tank to another one (Rh + H2SO4, T~35°C, Platinized Titanium Anode). Now when we make rhodium deposit on silver or palladium substrates, there are some black spots which appear on the surface of the deposit. Does anybody know how to fix this problem? Thanks in advance ;)

François Pignon
Plating shop employee - France


March 16, 2009

A. The most important thing I find to do when plating my pieces is to make sure I have a "fresh" cleaning solution and clean at 6v for about 40 seconds.

Then what I found caused spots is when you don't wash the piece under a running tap properly, and I mean blast it!
I actually hold my finger under the tap to create a type of water jet and make sure I spray ALL the cleaning solution off the piece.

if you stick your finger in the cleaning solution and try a wash your finger, notice how long that slimy/soapy feeling stays on. that same layer sits on the piece and if you don't wash it properly you get dark spots.

hope this helps?

Tommy

Tommy Dannhauser
fine jewelry - Durban South Africa


August 18, 2015

A. Try doing a gold strike before rhodium.

Pratap Acharya
- Mumbai, Maharashtra, India



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