Synthetics
Main article: Synthetic diamond
Six crystals of cubo-octahedral shapes, each about 2 millimeters in diameter. Two are pale blue, one is pale yellow, one is green-blue, one is dark blue and one green-yellow.
Synthetic diamonds of various colors grown by the high-pressure high-temperature technique
Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.[32]
The majority of commercially available synthetic diamonds are yellow and are produced by so called High Pressure High Temperature (HPHT) processes.[88] The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.[89]
A round, clear gemstone with many facets, the main face being hexagonal, surrounded by many smaller facets.
Colorless gem cut from diamond grown by chemical vapor deposition
Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.[90] This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).[36]
At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 1.2E+8 carats (24,000 kg). Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are.[91]
Simulants
Main article: Diamond simulant
A round sparkling, clear gemstone with many facets.
Gem-cut synthetic silicon carbide set in a ring
A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante. The most familiar diamond simulant to most consumers is cubic zirconia. The popular gemstone moissanite (silicon carbide) is often treated as a diamond simulant, although it is a gemstone in its own right. While moissanite looks similar to diamond, its main disadvantage as a diamond simulant is that cubic zirconia is far cheaper and arguably equally convincing. Both cubic zirconia and moissanite are produced synthetically.[92]
Enhancements
Main article: Diamond enhancement
Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond.[93]
Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance is diamond-like carbon—an amorphous carbonaceous material that has some physical properties similar to those of the diamond. Advertising suggests that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant. Techniques such as Raman spectroscopy should easily identify such a treatment.[94]
Identification
Early diamond identification tests included a scratch test relying on the superior hardness of diamond. This test is destructive, as a diamond can scratch diamond, and is rarely used nowadays. Instead, diamond identification relies on its superior thermal conductivity. Electronic thermal probes are widely used in the gemological centers to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds.[95]
Whereas the thermal probe can separate diamonds from most of their simulants, distinguishing between various types of diamond, for example synthetic or natural, irradiated or non-irradiated, etc., requires more advanced, optical techniques. Those techniques are also used for some diamonds simulants, such as silicon carbide, which pass the thermal conductivity test. Optical techniques can distinguish between natural diamonds and synthetic diamonds. They can also identify the vast majority of treated natural diamonds.[96] "Perfect" crystals (at the atomic lattice level) have never been found, so both natural and synthetic diamonds always possess characteristic imperfections, arising from the circumstances of their crystal growth, that allow them to be distinguished from each other.[97]
Laboratories use techniques such as spectroscopy, microscopy and luminescence under shortwave ultraviolet light to determine a diamond's origin.[96] They also use specially made instruments to aid them in the identification process. Two screening instruments are the DiamondSure and the DiamondView, both produced by the DTC and marketed by the GIA.[98]
Several methods for identifying synthetic diamonds can be performed, depending on the method of production and the color of the diamond. CVD diamonds can usually be identified by an orange fluorescence. D-J colored diamonds can be screened through the Swiss Gemmological Institute's[99] Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers.[97] Similarly, natural diamonds usually have minor imperfections and flaws, such as inclusions of foreign material, that are not seen in synthetic diamonds.
