Summary for rhodium electrodeposition dull Discussion
Rhodium electrodeposition problems in this thread mostly come down to the fact that rhodium is extremely thin and will not hide or brighten a dull base surface. Geoff Smith asked why rhodium looked perfect on polished pieces but darkened when rubbed on dull pieces; later, Baljit Singh reported that pen-plated rhodium over yellow-gold prongs stayed dull and blackish even after cleaning. Ted Mooney explained that rhodium plating is too thin to add specularity, so if the prongs are not bright before plating they will not be bright afterward; he suggested nickel plating or white bronze plating first. In a later question, Dharmesh Pattani described a white, burned-looking finish on polished 18k gold, and Mark Baker advised checking rhodium metal concentration and sulfuric acid range, while Neil Bell added to lower both temperature and voltage to avoid excess hydrogen. Ayushi Lingayat’s grainy finish question was met with a request for more process details.
2007
Q. Hello, I have a problem. I am producing rhodium sulphate. It’s electrodeposition is perfect in color, resistance, brightness in polished pieces but, when used in dull pieces, it becomes dark in color when I scrub my fingers in this piece. What’s wrong. What can I do?
Luana Macedo Vieira de Souza Leite
producer of rhodium sulphate
Ribeirão Preto, São Paulo, Brasil
A. Luna
Rhodium plating is always applied very thin. This is because of cost and stress in thick deposits.
Because it is thin, the brightness depends largely on the brightness of the substrate.
To make a dull surface bright by plating requires that the process has leveling properties and I would not expect any rhodium solution to do that.
It sounds like you already have an acceptable process
Geoff Smith
Hampshire, England
2007
Q. Hi
We use pen plating for plating the rhodium over prongs of yellow gold. But the problem is, even after thorough cleaning, the rhodium remains dull and does not shine at all. It has blackness over it. Cam anybody suggest the solution?
Baljit Singh
– haryana, India
January 30, 2016
A. Hi Baljit. Rhodium plating is too thin to add brightness (specularity). If the prongs are not bright before rhodium plating they will not be bright after. You may need to nickel plate or white bronze plate before the rhodium. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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January 2016
Q. Sir,
Thank you very much for the advice. Although I am not aware about the product for nickel plating through pen plating system. Kindly let me know, if there is any Nickel Pen-Plating Solution or if it can be prepared at home.
Baljit Singh [returning]
– haryana, India
January 31, 2016
A. Hi, Baljit. You can google for suppliers of brush plating solutions. While I will not tell you that you cannot prepare your own nickel plating solution, I can tell you that professionals don’t do so despite their knowledge and high volumes … so I don’t think you ought to. And if you elect to use white bronze, that is a very complicated process which requires balancing three metals. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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Need project assistance? $100/hr.
February 2016
Q. Hello sir; I am using white rhodium for fully polished surface of 18k gold but after plating white color rashes come like a burn surface. Voltage is around 4 to 5 and temperature 60 °C.
Dharmesh Pattani
Jewellery – United Arab Emirates
May 19, 2019
A. Hello Dharmesh,
You will want to make sure your Rhodium metal is sufficient in the bath. Plating at the same voltage as you do normally with a low metal content, you will see this condition. The sulfuric acid should also be checked to see if it is within range. Most rhodium bath solutions run at 2-2.5 g/l. Hope this helps.
Mark Baker
Electronics plating – Winston-Salem, North Carolina USA
May 24, 2019
A. In addition to what Mark says lower both your temperature and voltage. Your plating out more hydrogen than you need to.
Neil Bell
Albuquerque, New Mexico
May 24, 2019
Q. Hi. I am currently using Rhodium plating solution. I am plating at very low current (4 ASF). I have been observing grainy finish. The data sheet recommends to plate between 4 ASF to 8 ASF.
Would appreciate suggestions
Ayushi Lingayat
– Austin Texas
October 16, 2020
A. Hi Ayushi. Please fully introduce yourself and your situation for the best chance of people being able to help.
Unfortunately, we don’t know whether this is your very first attempt to rhodium plate so you are unaware that the rhodium will not smooth out a rough unpolished surface, or whether you’ve done several items successfully but now the solution is contaminated/exhausted, or whether you are a highly experienced rhodium plater who usually knows exactly what to look for but you’ve encountered this problem for the first time.
What are you plating, what is it made of, and is there a layer of other plating between the substrate and the rhodium please?
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
October 2020