Letter 13096

Gold underplating 

Please tell me the recommended quality and thickness of the gold underlayer for Rhodium plating. I understand the reason for the gold underlayer (is it called "Flashing"?) is to get better adhesion of the Rhodium. If that is not the correct reason, please correct my thinking.

Rhonda Smiley
- Kansas City, MO, USA

You do not say what your application is or what metal you are trying to plate over but generally speaking gold is not used as an under plate for rhodium. There may be some particular engineering applications or special conditions where this is the specified method and the thickness would depend on those circumstances.

Neil Bell
Red Sky Plating - Albuquerque, New Mexico, USA

I have heard of the contact points on low voltage electromechanical relays being gold plated with a flash of rhodium. In this case I believe the gold is there as the essential contact material while the rhodium is there to prevent the gold contacts from "cold welding" together. But this is only my faint recollection of the reason for the combination.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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