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Getting bright white rhodium on 18K white gold jewelry [India]

We are in to jewelry manufacturing, we do a lot of 18 K white gold jewelry, where we do rhodium over an undercoat of palladium.
Our smaller products come out good where the larger pieces, specially the jewelry piece which has a lot of sockets looks greyish black at the back when compared to the jewelry pieces from far eastern countries like China or Hong Kong.

Khushroo Kotwal
Asst Director production - Mumbai, Maharashtra, India
July 27, 2010

Hi, Khushroo. A picture would help as I'm not quite sure what you mean by the "back" and a "lot of sockets", but bright plating is sensitive to current density, and current density is proportional to solution resistance -- which is to say that protruding asperities get a very high current density and holes and depressions a very low current density. It may be that the complex jewelry cannot be plated simply by hanging it on a wire and dipping it.

It's hard to say if the rigging is inadequate, or the plating solution can be improved, or if brush plating would be better. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 27, 2010

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July 28, 2010

Dear Kushroo,

It is possible to get the finish like any body else.The problem is that we only compare and complain but rarely try to explore what those people are doing to get those finishes.
Firstly I am sure you must be having a low bath volume.
To plate bigger article we must have a big bath volume. 5 ltrs volume is considered big in India!
Make sure that you have good precleaning and activating.
Make sure you have minimum 2 gram Rh metal/ ltr bath
Make sure pre plating palladium covers LCD areas very well.
You may have increase plating time to get good coverage in the Low Current Density(LCD) areas.
Good luck

T.K. Mohan
plating process supplier - Mumbai, India

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August 2, 2010

Hi,

do you have a good cleaning and activation system, I would suggest you to go for an ultrasonic cleaning system,also a perfect mechanical polishing ,secondly the current density applied and the metal content in the bath plays an important role too.

Best Regards

Praveen Kumar
plating process supplier
Mumbai, India

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August 25, 2010

hi khushroo,
I'm 100% sure that your cleaning for pieces is not proper. you boil it in HCl then make directly ultra in base media solution, steam that article and then make a Rh plating, see the results.

bhupesh mulik
jeweller - Mumbai, India