How Does Vapor Deposition Create Mystic Topaz and Aqua Aura Quartz?


A mystic topaz is an enhanced topaz gemstone. The vapor deposition process creates a multicolor surface coating on the stone. “Tulip (1),” 14kt white gold pendent with mystic topaz, by Mark Somma is licensed under CC By 2.0
A mystic topaz is an enhanced gemstone. The vapor deposition process creates a multicolored coating on the surface of the topaz. “Tulip (1),” 14kt white gold pendant with mystic topaz, by Mark Somma is licensed under CC By 2.0

Question

I know that mystic topaz and aqua aura quartz are created using an electrodeposition sputtering process. Gold or other metals are “sputtered” as a coating on gemstones. My question is: how? Can someone please explain how vapor deposition works?

How Vapor Deposition Creates A Metal Coating

In the very distant past, I 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 gave me a vacuum of less than one millimeter of mercury pressure. (But that is only useful for sputtering. That 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 with atoms of very active oxygen, which cleaned up any microscopic traces of organic material remaining after a very thorough initial cleaning. (In my case, the jobs were 3-inch glass concave lenses to be made into precise concave mirrors).

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

“PICT0111.JPG,” DC-PECVD system in action. DC plasma (violet) improves the growth conditions for carbon nanotubes in this chemical vapor deposition chamber. A heating element (red) provides the necessary substrate temperature, by Polyparadigm. Public domain.
“PICT0111.JPG,” DC-PECVD system in action. DC plasma (violet) improves the growth conditions for carbon nanotubes in this chemical vapor deposition chamber. A heating element (red) provides the necessary substrate temperature, by Polyparadigm. Public domain.

Next, a low-voltage, high-amperage current (about 50 amps at 3 volts) was applied to a heavy tungsten coil. The coil became white hot. Bits of gold, copper, and aluminum (or other metals which had been clipped on to it) began to boil and evaporated. Since there was very little atmosphere in the jar at this stage, the metal atoms got sufficient energy to travel in straight lines without colliding with air molecules anywhere in the jar. These metal atoms then coated the jar and anything inside it.

Sometimes, instead of using a tungsten coil, a little boat-shaped dish is used to contain the metal to be evaporated. Pure silica is often used, too. The vapor deposition process is completely controllable. You can create a coat of any thickness up to a micron or two. You can create an iridescent effect over rocks, glass, cabochons, or other cut gemstones.

And there you have it. More than you ever wanted to know about vapor deposition!

Cheers,

John Burgess

Aqua aura quartz is created by coating a quartz piece with gold through a vapor deposition process. “Aqua Aura Quartz Crystal 2” by mangovall is licensed under CC By-ND 2.0
Aqua aura quartz is created by coating a quartz piece with gold through a vapor deposition process. “Aqua Aura Quartz Crystal 2” by mangovall is licensed under CC By-ND 2.0

More Applications Of Vapor Deposition

Vapor deposition is also called vacuum deposition. The process is widely used. In electron microscopy, viewing samples are gold coated this way, since the electron microscope can only accurately image a conductive surface. Plastics can also be “metalized.” Some plastic toy models have chromed parts made in this manner.

It’s possible to hook up multiple electrodes or coils simultaneously in the vapor deposition process. Since they don’t have to be the same materials, you can deposit layers of a metal mixture that might be quite hard to produce by other means.

Hope this helps,

Peter Rowe

“Color - Mystic Topaz” by Sandy Roberts is licensed under CC By 2.0
“Color – Mystic Topaz” by Sandy Roberts is licensed under CC By 2.0