How Vapor Deposition Creates A Metal Coating

I once built and operated a machine for vapor deposition. Imagine a glass bell jar connected to very powerful vacuum pumps. I had a good mechanical pump that created a vacuum of less than one millimeter of mercury pressure. But that’s only useful for sputtering. Evaporation requires a fairly high-voltage arc and electrodes composed of the metal that you want to deposit on a gemstone or other surface. Sputtering doesn’t give quite as good a result as evaporation.

At that pressure, I activated a pair of large rings at a voltage of 10,000v AC. This bombarded the job (in my case, 3-inch concave glass lenses) with atoms of very active oxygen, which cleaned up any microscopic traces of organic material remaining after a very thorough initial cleaning.

During this bombardment process, the entire bell jar glowed with a pale violet-pink light. After a few seconds, I switched this off, and the oil diffusion pump started up. This pump had no moving parts but could pull a vacuum of 0.00001 mm of mercury pressure, but only if the mechanical “backing pump” had removed the majority of the air first.

Next, I applied a…