Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Rhodium plating problems and troubleshooting
Q. Dear Sir :
I am now doing rhodium plating in spectacle frame. After rhodium plating, I find it has an adhesion problem if I plate another gold plating over it. Does anyone can suggest me a solution. Besides is there any brightener use in rhodium solution ?
Edmond Yeung1998
1998
A. Edmond,
You do not tell us what if any undercoat you use prior to rhodium. This will be the cause of latter bad adhesion. We have found that a strike in a cyanide gold over bright nickel gives the best adhesion and least problems with coverage of rhodium. To my knowledge there are no "brighteners" used in rhodium and our solution (Sel Rex) is simply rhodium sulphate and sulfuric acid.
Bob Lynch
plating company - Sydney, Australia
Q. Dear Sirs
I have a similar question as Edmond.
I am rhodium-ing 14k white gold ,but I have a brown spot on the shanks of the rings where they are hung, and comparing to other products my rhodium is always darker. How can I have the best bright rhodium?
I am using titanium rods.and the voltage is on 6 to 7 volts at room temperature, if you could help me out I will really appreciate it. Thank you.
Serge Tahoulakian- Montreal Canada
2000
A. Usually gray colors depends on the organic compounds amount.
I strongly suggest to check your operations and clean everything with coal.
Massimo Cappellini- Vicenza Italy
2000
Ed. note: by 'coal', Mr. Cappellini presumably means activated charcoal.
Q. I am a chemical engineer for electroplating industry. Now I got a problem for Rh plating. First I would like to know how we can remove the Rhodium deposit after plating. Second if the Rhodium plating is contaminated by metallic impurities. What can we do to remove them.
Thank you,
Scotty Wong- Hong Kong
2001
2001
A. You are not going to remove rhodium with chemicals so you will have to sand or polish it off. Metallic impurities can be precipitated using ferrocyanide.
I hope this helps.
Neil BellRed Sky Plating
Albuquerque, New Mexico
Q. In my humble opinion, Rhodium plating has always been a difficult process to the jeweler. I have started Rhodium plating about a month ago, and I am experiencing some difficulties when I plate with Rhodium on 18K white gold. I am abiding to the rules of Rhodium plating such as: good buffing, electrocleaning, etc. However, when I nickel plate prior to Rhodium, I notice on certain pieces grey, matt, dull areas as burnt areas. I give 120 °F and 2 volts to the rectifier and 2 minutes timing.
What in your opinion is causing this?
Joseph TantiJosies - Malta
2001
A. I think 120 degrees is low for a nickel bath, but why are you nickel plating your 18K white gold before rhodium? You should get excellent results plating rhodium directly over gold and it is a good idea to avoid nickel on items which will be worn against the skin.
Neil BellRed Sky Plating
Albuquerque, New Mexico
2001
A. Why do you use nickel plating over 18K white gold?
Its an old technique!
People prefer nickel-free jewelry nowadays as science revealed that nickel can cause skin-cancer if worn constantly.
After electrocleaning, give the article an 'acid-wash' followed by dipping it in rhodium-bath.
Avoid using nickel. It's not recommended.
Sudeep Sethi- Indore. MP, India
2001
There is no question that a lot of people suffer a skin allergy to nickel, Mr. Sethi, and I agree with you that nickel doesn't belong in jewelry. But I think your assertion that "science revealed that nickel can cause skin-cancer" is an overstatement. Can you reference any published document that asserts this? Thanks.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2001
A. Don't forget a pure gold underlayer for the Rhodium.
Michael Brewington- Salisbury, Maryland, USA
2001
Acid wash before rhodium plating
Q. Mr. Sethi suggested an "acid wash" prior to rhodium bath. Please could you kindly explain further what do you mean by 'acid wash'. How is it prepared and what type of acid is used for this type of wash. Does the acid wash need to be warmed up? To what temperature? Do you need to rinse again with distilled water after the acid wash?
Thank you in anticipation.
Joseph Tanti [returning]Josie - Malta
2001
A. Hi,
First do electrodegreasing (cathodic) then 2 water rinse then 5-10% sulfuric acid rinse (room temp) then dm water rinse and rhodium plate. And much brilliant white finish product available are Degussa TD, Heraeus K-20 or Metakems Dekor bath.
Good luck,
Qutubuddin Saify- Ajman, U.A.E
2001
Inconsistent plating thickness on rhodium plated ring
Q. I am studying about plating rhodium method. I plated a silver ring but I established different thickness areas on the ring. How can I solve this problem?
Serkan CeylanSakarya University - Erenler, Sakarya, Turkey
2002
2002
A. Hi, Serkan. Check into Faraday's Law of Electrolysis, which tells us that the plating deposits exactly where the electricity goes, and in exact proportion. Then check into Ohm's Law, which says the current is the voltage divided by the resistance -- and you will see the tough truth that you would need to get the anodes to conform exactly to the ring to get the resistance the same to all spots, and thus the current and thus the plating thickness. Then you'll have to decide on what compromises to make between perfect distribution and practicality.
For some plating processes, like acid copper, there are some addition agents that are of some help in evening out the thickness distribution, but I don't think any such agents work in rhodium plating. Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Nickel plating under rhodium plating
Q. 1 - Can I use nickel plating before rhodium to get better result?
2 - How to get more white brightening in gold plating by rhodium?
thanks
gold - cairo, egypt
July 26, 2012
A. Hi Yaser.
1. Yes, nickel plating can be done before rhodium, but due to widespread nickel allergies and some countries outlawing nickel plating in jewelry; white bronze before rhodium would be better. That is, of course, if you don't plate directly onto the white gold as Neil Bell suggests.
2. Sorry, I haven't personally heard of brightening a gold plating bath with rhodium additions.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 26, 2012
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Ed. note: Readers may also wish to review:
Topic 20395, "Rhodium plating Q&As, woes & problems" and
Topic 42108, "Rhodium Spotting Problems: black spots, brown spots"
Or search the site for many others.
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