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Nickel free rhodium on brass [Canada]

Q. How can I have a durable finishing rhodium on brass without Nickel?

Julie James
Gemologist - Canada
July 22, 2010

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July 27, 2010

No. It is almost impossible to plate rhodium (in production outside of the laboratory) without stress cracks. Then the copper and zinc migrate right through and corrode on top. You must have a barrier, probably nickel or palladium.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

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July 28, 2010

For Nickel free process White bronze under coat is most preferable as palladium is costlier.
Regards

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

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July 30, 2010

So called "White Bronze" will not fully protect as a diffusion or migration barrier. Nickel and Palladium will stop migration.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

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July 30, 2010

Dear Robert,
It is understood and proven that the 3 microns of White Bronze will do the job of protection in terms of barrier layer of 10 microns of Nickel which is equal to 0.2 Microns of palladium.
In the case of White Bronze, being an alloy plating one has to make sure to apply proper amperage( approx. 1 amp/dm.square) to get the prescribed percentage ratio of deposit viz. 65:35:5 - Copper:tin:zinc.
Whatever failure which came into my notice was because of careless handling of the bath and also because of giving less than thickness of 3 microns.
Honestly,I feel the 'so called White Bronze' is now becoming technically proven alternative in Nickel free jewellery as Palladium price is becoming not affordable.
Regards

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

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Thank you for your answer.

I already use our plating is copper + 80 mils silver + 10~13 palladium + 2 mils rhodium, and I have a lot of problems. The plating is not durable. If I put white bronze this is will be better?

Thank you for your help.

Julie

Julie James
- Canada
August 4, 2010

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Hi, Julie. A mil is a thousandth of an inch; I'm very confident that you are not applying the thicknesses that you say. You probably mean millionths of an inch?

2 millionths of an inch of rhodium may offer some degree of tarnish prevention until the item is sold, but it is probably not even thick enough to be visible, let alone to offer wear resistance. I am not a jewelry plater, but if you want a bright nickel-like look without nickel, I would replace that silver with about 10x as much white bronze, and then continue with the palladium and rhodium.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 5, 2010

P.S.: I responded to your followup email as its own entity without reviewing the earlier parts of the thread, and do not mean to contradict TK Mohans suggestion that a white bronze plating thickness of 3 microns is adequate.