Q. I am a jewelry artisan and take pieces cut out of sterling silver sheet and have them gold-plated by a local plating shop using a nickel-free process. The plating thickness is approximately 0.4 microns. My problem is that the gold plating isn’t durable enough and begins to tarnish after about six months or so. Is there anything I can do to prevent the gold from tarnishing? —F.P.
A. The problem you are observing occurs when gold is plated on a base metal such as copper, zinc or silver. In your case, the silver tends to migrate into the gold layer. This process is dependent on temperature and time. The gold does not really tarnish; what you are seeing is the formation of a silver/gold intermetallic compound. This compound discolors the gold layer.
The classic solution to this problem is to plate a barrier layer such as nickel on the base material and then plate gold on the nickel. Introducing nickel as a barrier layer is not an acceptable solution here, however, because of issues with nickel allergies. Plating a heavier layer of gold will slow this process down, but this is obviously more expensive and your plating vendor may be unable to give you a heavier process. Palladium also makes a good barrier layer, but it is very pricey.
Another solution that many plating people are not aware of is “white bronze,” an alloy consisting of copper tin and zinc that functions as a replacement for nickel in many jewelry applications. White bronze also is known as albaloy, miralloy and optalloy. Talk to your plating vendor and see if he is familiar with this plating bath.