Coating Cast Zinc Jewelry

Q. I would like to comment on “Coating Plated Zinc Jewelry” in your November column. We have been producing plated zinc die castings for 50 years and have been successfully applying clear e-coat to them for 12 years. We apply copper and nickel, followed by brass, bronze or gold, and then apply a 20-micron-thick clear e-coat and bake at 350°F for 40 min.

The key, of course is a dense, porosity-free casting, which we strive to produce continuously. I would greatly appreciate you forwarding our name to your reader—maybe we can help. L.J.

A. In response to that question about using e-coat on cast zinc jewelry, I agreed that high baking temperatures could cause problems with zinc castings, and suggested the reader find a durable, clear e-coat finish that would cure at lower temperatures or use a spray coating with a low baking temperature instead. I referred him to PFOnline to find e-coat paint and equipment suppliers.

As L.J. points out, the key to his success in baking on a clear e-coat is a dense, porosity-free casting. Coating porous castings using baking paints can be a problem because porous castings of most metals can release trapped gasses during the baking cycle, resulting in blisters in the coating. Two solutions to this problem are degassing the casting before coating and producing denser, porosity-free castings.