Monday, August 29, 2016

Synthetic Diamonds - De Beers' DiamondSure

An HPHT press, which is used in the production of lab-grown diamonds.
Dating back to the 19th century, there have been many claims for the creation of diamond in a lab. For many years conventional wisdom was that diamond would form only under conditions of high pressure and high temperature (HPHT).
The first commercially available “manmade” diamond was produced at high pressure and high temperature by General Electric in 1956. HPHT growth imitates natural diamond formation, but with carefully selected input materials to catalyze crystal growth.

Today, billions of carats of diamonds are manufactured annually by the HPHT process, mostly for industrial applications.
In 1954 a patent was issued for another type of diamond growth: the CVD (chemical vapor deposition) process. In the late 1980s, scientists discovered how to reproducibly grow diamond using the CVD process.

The CVD process is quite different from natural diamond formation. It produces diamond from a heated mixture of a hydrocarbon gas (typically methane) and hydrogen in a vacuum chamber at very low pressures.

The inside of a CVD diamond chamber.
The CVD process produces gem-quality synthetic diamond of great beauty, with properties virtually identical to those of natural diamond. Because of their high purity, these CVD products are type IIa.
Detection has advanced to the point where any CVD-grown sample can be identified with certainty. The CVD growth process itself occurs under conditions that bring about readily detectable features, including:

1. a low-pressure, highly energetic hydrogen-rich environment
2. the presence of silicon from grower parts
3. the presence of residual nitrogen in the grower
4. the layer-by-layer addition of carbon atoms on the growing surface

Because synthetic diamonds have identical properties to natural diamonds, it is almost impossible to determine a synthetic stone through a visual examination alone.

The difference in the growth process of a synthetic diamond compared to natural diamond can be identified using either cathode luminescence using electrons to highlight the stone's structure, or a camera to view the fluorescence pattern created on the surface of a polished stone with intense short wave ultraviolet light. Most colorless HPHT synthetics show phosphorescence - an afterglow - when the ultraviolet lamps are turned off. An identification can then be made by observing the fluorescence patterns characteristic of near-colorless synthetics.

The DiamondView enables lab staff to view tell-tale growth patterns for synthetic diamonds. The regular striations visible in the middle of this round diamond indicate it is a CVD-grown synthetic.
De Beers is preparing a defense against undisclosed synthetics in the form of a mass-screening device to fast-check melee for synthetics.

The device is in production. The Gemological Institute of America has developed, and will sell to the trade, a screening device for the detection of lab-grown as well as high-pressure, high-temperature (HPHT) treated diamonds.

Unveiled to members of the trade press in January 2015, the table-top device, called the DiamondCheck, is about the size of a toaster oven and can be used to test diamonds from one point to 10 carats in size.

The machine gives users one of three results about the inserted stone: it is a natural diamond; it is a diamond but should be referred to a lab for further testing because it could be synthetic or treated; or it is non-diamond material such as moissanite or cubic zirconia, though the device does not specify the type of material.