Synthetic Diamonds: Rough And Treated, Faceted

(via ICA Early Warning Flash, No.74, August 13, 1993) GIA GTL writes:

Background
Recently a 0.74 carat yellow rough crystal was submitted to the GIA Gem Trade Laboratory in New York for routine identification. Shortly thereafter, a 0.55 carat dark brownish orangy red round brilliant was submitted to GIA GTL for an origin of color determination. Examination of both specimens revealed that they were synthetic diamonds. It was further determined that the rough specimen had been annealed and that the faceted one had been irradiated and subsequently annealed.

Appearance
The habit of the rough crystal was predominantly cubic, with some octahedral and dodecahedral faces. Smooth cube, and to a lesser extent, dodecahedral, faces are seen only on synthetic diamonds.

Magnification/magnetism
Both the rough and faceted pieces contained fairly large inclusions with a metallic luster. When suspended at the end of a thread, both were attached to a magnet, actually attaching to it. This reaction has been noted to date only with synthetic diamonds containing large, magnetic inclusions derived from the metallic flux in which they are produced.

The two showed similar patterns of ultraviolet luminescence and color zoning, forming essentially a square; the faceted piece also revealed this in the form of graining. This growth pattern was centered roughly in the middle of the base of the crystal and on the table of the round brilliant. Octagonal to square patterns are commonly seen in synthetic diamonds, but not in natural diamonds.

Ultraviolet luminescence
The ultraviolet luminescence of both pieces was stronger in short wave than long wave radiation. They both emitted a moderate to strong green fluorescence along the pattern described above in short wave UV radiation, with a weaker green reaction in long wave. The round brilliant also emitted a moderate orange fluorescence in short wave. Gem quality yellow synthetic diamonds previously examined by GIA Research and GIA GTL personnel have shown luminescence in short wave exclusively. The reactions noted in the two specimens under discussion would therefore appear to be from a source other than those we have previously documented in the gemological literature.

UV/Visible/IR spectroscopy
Spectroscopy helped to further characterize the specimens. Infrared spectroscopy showed them both to be essentially type Ib, as are most yellow synthetic diamonds. However, they both also showed a IaA character. This has not previously been observed in gem quality synthetic diamonds.

In the visible range, the round brilliant showed a number of sharp lines between 500 and 700bn at liquid nitrogen temperature. These features were noted both in the hand held spectroscope and on the chart of the spectrometer. Some of these lines have never been observed in natural diamond but have been reported in synthetic diamonds.

Finally, the presence of the features typical of treated pink diamonds in the spectrum of the red brilliant (in addition to other lines mentioned above) and a small HIb peak in the infrared prove that it had been irradiated and subsequently annealed. The yellow crystal also shows a line at about 637nm, which suggests that it, too, had been subjected to annealing.

Conclusion
The above characteristics clearly identify both the crystal and round brilliant as synthetic diamonds. However, some of their properties are slightly different from what we have observed before in yellow gem quality synthetic diamonds. Interestingly, virtually all the features noted are consistent with those of a group of Russian yellow synthetic diamonds currently being studied by GIA Research and the GIA GTL.