By Joe C. C. Yuan -- G.G., D.G.A.

Since January 1999, Russian-made colorless synthetic diamond of gem quality (Fig. 3-2) has been available on the U.S. market, posing as a significant threat to the diamond trade and calling for an early understanding of its characteristics and its identification.

The author has obtained forty pieces of rough crystals, cut and polished, which were later sent to the following organizations for testing and analysis:

Dr. Eugene Huang at the Institute of Earth Science under the Academia Sinica in Taiwan

Dr. Ming Sheng Peng and Ms. Bin Lin at the Zhong Shan University in China

Throughout the world, manufacturers who produce wholesale quantities of synthetic diamonds in sizable single crystals that include De Beers (its lab in South Africa), General Electric of United States, Sumimoto of Japan and several others in Russia. Synthetic diamonds produced by the aforesaid first three organizations are only for study or industrial use and are not sold as gem diamonds. However, those produced in Russia do not have to abide by this restriction, and hence they are cut and has found their way to the diamond trade. In 1996, Chatham of the US came up with 100 nearly colorless synthetic diamond crystals ranging from 0.20 to 0.70 carat each. As they were heavily included, they were not fit for use in gem quality diamond, but their country of origin was none other than Russia.

The Russian synthesis of large single-crystal diamonds differs from the "Belt" method of the other three producers. Instead, a "split sphere" is used. The reaction chamber remains cubic in form. It is surrounded by six pyramids of half octahedrons of tungsten carbide, forming a complete octahedron. On each crystal face of the octahedron, there is another layer spherical compressor. The pressure is about 55 to 65 kbar. Heating is achieved by means of electricity from 1350 to 1700^oC. Catalysts are iron, sulfur, aluminum, nickel, chlorine, etc. There is a seed crystal at both ends of the reaction chamber, which has constant and stable pressure. The temperature are maintained through the seed ends of the chamber. The temperature is regulated slightly lower about 30^oC than the middle of the chamber. It takes more than five days to grow to one carat size crystal.

The appearance of the crystal is a combination of a cube and an octahedron (Fig. 3-1). The surface of the crystal appears to be of a regular or irregular dendrite form as shown in Fig. 3-3. The seed in the center of the largest {100} crystal face appears as a square, and the large, rectangular bulge on its outside is the trace left over by the container that fixed the seed, seen in Fig. 3-4 and 3-5.

The higher the growing temperature, the better the development of the crystal face {111} to resemble a octahedron. On the {111} of sample #6, there is a corrosion pit with terrace-like walls (Fig. 3-6), which after gold plating, it has been photographed with scanning electronic microscope at magnification of 50X to 500X. Fig. 3-6, for instance, was taken at 100X.

Weight: The forty samples of crystals weighing between 0.23 to 1.18 carats each, have been cut to polished diamonds of 0.07 carat to 0.45 carat. The rough diamond crystal received by the distributor in the US ranges from 0.19 carat to 1.24 carats.

Color Grade: From near colorless to faint yellow corresponding to the range from G to K on the GIA scale. The color is mostly of a darker tone. Even the IIa type (see infrared spectrum in Fig. 3-13) which is mostly near colorless, is low in transparency so that it may reach the G grade only. The remaining few are faint yellow. Infrared and electron microscope scanning all show the absence of nitrogen.

Inclusions: Inclusions are primarily metallic inclusions (Fig. 3-10) and feather (feather-like cracks). The highest clarity grade is SI₂ with the most heavily included down to I₂ or I₃. The metallic inclusions are typical of those seen in yellow synthetic diamonds, including flakes, needles, regular or irregular shaped geometric figures, octahedron, dodecahedrons, combination of hexahedron and octahedron, etc. (Fig. 3-7, 3-8, and 3-9). Positions are usually of a symmetrical arrangement. The metal inclusions reflect white and spectrum colors (Fig. 3-11). Feathers are mostly caused by the uneven release of strain within the stone at the time of cutting and polishing. The majority of them look transparent (Fig. 3-12).

Magnetism: Magnetism increases with the amount of metallic inclusions. Eighty percent of these samples can be attracted and picked by a strong magnet. The rest can be detected by placing a small piece of paper on the surface of water. Then place the diamond on top of the paper. When a magnet is placed near the diamond, it will be flow toward the magnet.

Anomalous Double Refraction: Under the crossed polaroids, these diamonds show anomalous double refraction in the form of a thin cross.

Fluorescence and Phosphorescence Under Ultraviolet Rays: Under long-wave ultraviolet rays, three of the 20 samples tested, show faint fluorescence while the remaining 17 are inert. Under short wave, four are inert while the remaining 16 show fluorescence as follows:

After a few seconds under short wave, the source of light is turned off and those that have shown fluorescence continue to show phosphorescence, which last from a few seconds to over a minute before total extinction. With few of them, only a faint shadow of a cross is seen in the center of the whole stone that shows fluorescence and phosphorescence. This is unlike the yellow synthetic diamonds which show regional geometric fluorescence patterns.

Spectroscopy: A spectroscope of the table-type is used. Observation reveals the following:

Infrared Spectroscopy: Spectra have been obtained of the twenty near colorless synthetics by the means of the FTIR spectroscope. Under transmitted light, it shows the absence of any absorption peak in the 1000-1500 cm^-1 range where the nitrogen peak can be found if nitrogen is present. Therefore, the stones are of IIa type (Fig. 3-13).

Analysis of Inclusions by Means of Energy-disposition Electroscope: Inclusions in two samples are exposed after the covering surfaces are polished off. After being plated with carbon, the application of electron microprobe shows on its EDAX 9100 analyzer. The contents and their percentage as follows (Fig 3-14 & 3-15):

Of the contents, iron is the most abundant. Sulfur in sample #7, as well as aluminum, chlorine, and copper in sample #8 are items that call for further investigation. Another sample, which is sample #3, has been scanned with electron probe and its wavelength dispersion spectroscope after its surface has been plated with carbon, at wavelengths of nitrogen, oxygen and carbon. It has been found to contain carbon only and is entirely free of nitrogen and oxygen, which is found to be consistent with FTIR spectrum obtained from sample #3.

X-ray Powder Diffraction: The author collected some diamond powder from girdle brutting for specimen of this experiment. The instrument used is Japanese D/Max-IIIA model, X-ray diffraction meter. It uses a copper target under a current of 3.5 KV and 25 mA. From the X-ray diffraction diagram (Fig. 3-16), the highest peak is 2.069A^o, which is the distance between web faces of {111}. The distance is larger than 2.0594A^o of a natural diamond. Meaning also that the carbon atoms are more closely arranged at the same web face {111} and hence the higher hardness of the synthetic diamond than that of natural diamond, which evident as more difficulty in cutting. The d value of the other three diffraction peak are 3.86A^o, 2.98A^o, and 2.85A^o. This shows its material phrase is Melnikovite of which the iron in the sulfite co-exists in Fe²⁺ and Fe³⁺ state. This is used as the flux in the growth of synthetic diamond.

Images from the DiamondView™ : The DiamondView™ was developed at De Beers DTC Research Centre, Maidenhead, UK. The DiamondView™ uses short wave ultraviolet light to produce a fluorescence image of the surface of a polished diamond from which the growth structure maybe determined. The fluorescence pattern of a natural diamonds are different in comparison to synthetic diamonds. The author, Dr. Paul M. Spear of DTC Research Centre, and Mr. David A. Weinstein, M.S., G.G. of IGI conducted some examinations with the DiamondView™ for this research.

As we can see in Fig. 3-17, it is a Russian grown synthetic yellow brilliant cut diamond weight 0.38 ct. View of the crown shows characteristic cross-shaped fluorescence pattern. Stone dominated by octahedral growth sectors.

In Fig. 3-18 shows the pavilion view of stone in the Fig. 3-17. It shows similar characteristic cross-shaped fluorescence.

In Fig. 3-19, it is a Russian grown synthetic yellow princess cut diamond weight 0.61 ct. View of the crown shows characteristic multi-growth sector fluorescence pattern in the center of the table facet.

In Fig. 3-20, it is a Russian grown synthetic yellow princess cut diamond weight 0.68 ct with the characteristic cross-shaped fluorescence pattern in the center of the table facet.

In Fig. 3-21 & 3-22, this synthetic yellow diamond weight 0.38 ct has been manufactured by De Beers as we were told, and has been made into an anvil for use in ultra-high pressure experiments. This synthetic stone is characterized by strongly fluorescence and inert growth section. The ‘umbrella’ fluorescence pattern around the culet facet was caused by stress created when the diamond was under ultra-high pressures.

Fig. 3-23 shows the Russian grown colorless but brilliant cut diamond, weigh 0.07 ct. The fluorescence is evening distributed on the crown without any characteristic fluorescence pattern. It is probably the cubic growth sector.

Fig. 3-24 is another Russian grown colorless diamond weigh 0.07 ct. The strength of fluorescence is not as strong as Fig. 3-23. It is showing square shape grown section in the center of the crown. It is octahedral sector.

Fig. 3-25 is the bottom view of diamond in Fig. 3-23. It is showing a bowtie-shape grown sectors. It is octahedral sectors.

Fig. 3-26 is a Russian grown colorless brilliant cut diamond weigh 0.31 ct. Bottom side view which shows grown sectors in the middle of pavilion facets. Like the previous stones it is also octahedral sectors.

The Russian-made colorless synthetic diamond is gradually becoming popular. Though the present market price is more than double that of natural diamond, it is believed that eventually, it will be in a position to compete against the natural diamond after the producing factory improves its productivity to upgrade its quality and lower its cost.

Before the DiamondSure™ and the DiamondView™ are popularized, which are instrument invented by De Beers for the detection of the synthetic from the natural diamond. The dealers will have to rely on magnified observation of its metallic inclusions and their magnetism as the main characteristics of identification with the fluorescence and phosphorescence from the short-wave ultraviolet rays as a supplementary characteristic.