The Winter issue of Gems & Gemology offers the first in-depth look at the new chemical vapor deposition (CVD) synthetic diamonds produced by Apollo Diamond Inc. of Boston, Massachusetts.

Apollo founder Robert Linares, one of the co-authors of the study, submitted both rough and polished samples to GIA researchers for study. The rough CVD-produced diamonds are tabular or block shaped, much different from natural diamonds or synthetic diamonds produced by the traditional high pressure/high temperature (HPHT) techniques. This is because the CVD process works much differently from the processes that form natural and most synthetic diamonds.

The CVD technique involves combining certain gasses and heat (but very low pressure) to create a synthetic diamond film over a solid substrate. Apollo discovered a method to create single-crystal, gem-quality synthetic diamonds with this process.

GIA researchers Wuyi Wang, Thomas M. Moses, James Shigley and Matthew Hall conducted gemological tests on the Apollo samples. The faceted samples, all type IIa, were shallow cut because of the shape of the starting crystal. Viewing faceted stones through the table, the researchers found an evenly distributed faint to dark brown color with no graining or color zoning.

Some samples did show brown grain lines, however, when observed through the girdle. Compared to natural stones, the internal graining in the Apollo CVD synthetic diamonds is much thinner and sharper.

Other identification characteristics observed were orange fluorescence seen with the De Beers DiamondView, unusual black graphite inclusions, and distinctive spectral features. The researchers found that all of the CVD synthetic diamonds examined to-date could be positively identified in a well-equipped gemological laboratory by means of examination with a microscope, spectroscopic techniques and observation of luminescence reactions.

James E. Butler, an expert on CVD-diamond growth who is a researcher at the U.S. Naval Research Laboratory in Washington, D.C., also contributed to the article.

Legendary Gemologist
The Fall 2003 issue of G&G pays tribute to G. Robert Crowningshield, a pioneer of modern gemology, who spent more than 50 years with GIA. The article, co-authored by Moses and Shigley, notes that Crowningshield was already a budding authority on gemstones when he joined GIA in 1947 and rapidly began to make contributions to the science and practice of gemology.

In the 1950s, he was an innovator in the use of the spectroscope for gem identification. Though not the first to use the instrument for that purpose, he meticulously recorded the spectrum of every gemstone variety that came through the lab, creating a database that was then published in GIA’s Handbook of Gem Identification.

One of Crowningshield’s greatest contributions was the use of the spectro-scope to help the diamond industry overcome a crisis in confidence, by devising an identification method for detecting irradiated yellow diamonds. Later, Crowning-shield helped devise criteria for identifying natural-color black cultured pearls and tissue-nucleated freshwater cultured pearls. He also supported the late Richard T. Liddicoat in the development of the GIA International Diamond Grading System^TM.

Black Diamonds
The cover story of the Fall 2003 issue is a report on the cause of color in black diamonds, which have become extremely popular in designer jewelry. The article takes an in-depth look at Siberian-mined black diamonds. Natural facetable black diamonds are very rarely found in kimberlite and alluvial deposits. The Mir mine is the source for most of the black diamonds that emerge from Russia, which are polished primarily by Russian-related companies in the U.S. and Moscow.

The authors applied scanning and transmission electron microscopy to the difficult job of studying the nearly opaque diamonds and their inclusions, which are thought to be the cause of the black color. Their investigation revealed that the coloring of the black and extremely dark gray diamonds studied was caused primarily by the presence of inclusions of hematite, magnetite and iron.

The diamonds with the blackest color contained predominately magnetite inclusions, while the dark gray samples had inclusions of hematite and iron. Interestingly, graphite, which has been reported as the cause of black color in other black diamonds, was detected only in small amounts in two of the samples studied. Thus it cannot be responsible for the black color of these Siberian diamonds.

The authors also found that these diamonds had a high magnetic susceptibility, which may prove a useful criterion for separating natural from treated-color black diamonds.

Lab Notes
Three unusual type II diamonds recently went through the New York GIA Gem Laboratory. The type IIa (1.53 ct.) and IIb (5.69 cts. and 42.05 cts.) diamonds displayed unusual luminescence features and photoluminescence spectra that suggest a new type of crystal lattice defect. The smaller type IIb was graded Fancy grayish blue. The larger type IIb, which was only partially faceted (and thus not graded), displayed a strong blue color. It was reportedly mined in southern Africa.

Unlike most type IIb diamonds, these two fluoresced weak orange to long-wave ultraviolet radiation and moderate to strong yellow (with a very strong blue phosphorescence lasting more than 60 seconds) to short-wave UV. The type IIa, a D color, showed the same features.

The West Coast GIA Gem Laboratory examined a 12.7 mm orangy yellow cultured South Seas pearl that appeared to owe its color to a treatment process different from others previously encountered in the GIA lab. Magnification revealed a faint patchiness on the surface, and long-wave UV radiation produced a strong, slightly uneven, light greenish yellow fluorescence with an orange overtone in some areas.

These features are uncharacteristic for natural-color yellow (“golden”) cultured South Seas pearls.  UV-visible spectroscopy showed a prominent absorption line at 456 nm, unlike any UV-visible feature seen previously in either natural- or treated-color “golden” cultured pearls. These traits make this type of pearl treatment easily identifiable.