Nickel present in top layer of gold in gold over nickel plating

A. Pores in the gold deposit can result in nickel at the surface. If the object is heated nickel will diffuse to the surface. To assure no pores, be sure the nickel is properly cleaned and activated. And the thickness should be increased. I have found that it takes about 100 millionths of gold to be pore free in many cases.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])

A. Just a few points about your concerns regarding nickel allergies. Firstly, the only real way of avoiding it is to have a system that does not wear away or release nickel (i.e., use a nickel alloy). Plating 50 microinches (which I reckon is just about 1.2 microns) of gold onto jewellery will not last long, so the customer will soon be exposed to nickel again. Secondly, such thin layers of gold will be porous and leave nickel exposed. Thirdly, how did you do your analysis? If you used EDAX, the electron beam will penetrate a good few microns (depending on the voltage) into the "surface", so the emitted X-rays will show nickel. The ASTM spec you refer to allows gold to be hardened by either iron, cobalt or nickel, so make sure your supplier is using pure cobalt. I would recommend you either put a lot more gold down or avoid using nickel as an interlayer.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003