IGE Article: Identification of synthetic diamonds using basic gemological methods

Synthetic diamonds are beginning to enter the jewelry trade. While ruby, sapphire and emerald have already had their synthetic analogues for many decades, the diamond has taken longer to be obtained in the laboratory in quality, size and price suitable for use in jewelry. But they are here to stay. Currently, the prices of lab grown diamond engagement rings are already well below natural ones, although they still have a higher value than imitations, such as zirconia. It is difficult to assess the current ratio of gem-quality synthetic diamonds to natural ones. The purpose of this article is to explain some simple methods that can help you in this task.

Diamond synthesis methods

Currently, gem-quality synthetic diamonds, both in the colorless series and in fantasy colors, are obtained by two methods – HPHT (high pressure and high temperature) – high pressure and high temperature method, and CVD (chemical vapor deposition) – chemical vapor deposition method. The HPHT method was the first to bring gem-quality synthetic diamonds to the market, beginning in the 1990s and first in fancy colors. CVD diamonds for jewelry began to appear on the market in the late 2000s and are now also manufactured by various companies.

Identification of HPHT synthetic diamonds

The first step in identifying and grading a diamond is to examine the stone under magnification, preferably using a gemological microscope.  If opaque inclusions are observed, they must be studied very carefully using different illumination methods, such as fiber optics. Most natural diamonds belong to the so-called Cape series and present bluish fluorescence. In contrast, synthetic diamonds do not fluoresce bluish, are usually inert, or have a weak yellowish, greenish, or orange fluorescence. Type I diamonds are opaque to short-wave UV light. Colorless synthetic diamonds, both HPHT and CVD, belong to Type IIA. The metallic solvents used as the growth medium for HPHT synthetic diamonds often produce metal inclusions – from submicroscopic particles to inclusions visible to the naked eye. These inclusions are magnetic, and diamonds that present them can be attracted to a strong magnet.

Identification of CVD synthetic diamonds

In general, CVD synthetic diamonds are more difficult to identify with basic gemological methods than HPHTs, because they do not present metallic inclusions or marked phosphorescence in many cases. They are less numerous on the market today, compared to the HPHT synthesis. Fortunately, they also belong to type IIA, very rare in nature.

Microscopic observation

As for HPHT synthetic diamonds, careful microscopic observation of the diamond is very important as it could reveal typical characteristics of natural diamond. Some companies engrave the inscriptions of “LAB GROWN” or the like on the girdle of their CVD synthetic diamonds.

The behavior of CVD synthetic diamonds under UV light is similar to that of HPHT synthetic diamonds, and totally atypical for natural diamonds. The main techniques used for the detection of colorless synthetic diamonds in laboratories include infrared spectroscopy, ultra-short UV fluorescence microscopy and Photoluminescence at liquid nitrogen temperature. The application of basic gemological methods for the detection of colorless synthetic diamonds requires some experience and practice with diamonds of a known nature.