Plating White Metal

We plate and restore small antique items. Recently, we had the occassion to replate an old lamp with a white metal base. We attempted to plate with non-cyanide silver, acid electroless nickel and alkaline electroless nickel. All were unsuccessful and produced a lot of smut and some plating of exposed glass.What is the proper method for plating white metal? Do we need a preliminary copper strike or other special procedure? Any suggestions are greatly appreciated. Thanks.

Jay, You are on the right track with the copper strike idea. The problem you are encountering is that your base metal is primarily zinc and wants to dissolve in the plating baths you have tried thus far. Start by activating the part in 0.25% sulfuric acid, rinse well and then strike in a copper cyanide strike followed by a cyanide copper plate. The part can then be built up with the final deposits you require. If you don't have cyanide copper, you may be able to use a sulfamate nickel but the hydrogen overvoltage may be too great if your pH in the sulfamate tank is too low.