Tuesday, April 6, 2010

Colored Diamond Research From The GIA Newsletter

We are always trying to keep up on the newest technologies for enhancing the color of natural diamonds, as well as the techniques for identifying their treatment. Without the tireless research efforts of grading organizations such as the GIA, we would never be able to keep up with the field, and might get duped into purchasing lab created colored diamonds as HPHT color enhanced natural diamonds!

In the GIA's most resent newsletter, they uncovered a lot of 48 pink diamonds that were sold as pink HPHT color enhanced natural diamonds, but after detailed laboratory testing by the Gemological Association of All Japan, turned out to be CVD-grown synthetic diamonds HPHT treated pink!

Thank you to the Gemological Association of All Japan and GIA was sharing the news...Lesson is, buyers beware. All color or clarity enhanced as well as synthetic/cultured diamonds must be properly and honestly disclosed by the sellers at all stages of transaction!

Here is a reprint of the article from the GIA eBrief Newsletter, April 5, 2010.

Treated CVD-Grown Pink Synthetic Diamond Melee Submitted as Natural
The Gemmological Association of All Japan - Zenhokyo Laboratory recently examined 48 small orangy pink round brilliants submitted for color-origin identification. They were represented as natural diamonds treated by a high-pressure, high-temperature (HPHT) process. Six were in the 0.20-0.27 ct range, and the remainder were melee-size (less than 0.20 ct). Color grades ranged from Fancy Intense orangy pink to Light pinkish orange.
Microscopic examination revealed a few pinpoints in most of the samples. Several had black graphitization in cleavages and frosty etching on the surface - both signs of HPHT treatment. The pink color was evenly distributed. Most samples showed a streaked pattern of anomalous double refraction (ADR), but some revealed a “tatami”-like (cross hatched) pattern when observed in other directions. The samples fluoresced strong orange to long- and short-wave ultraviolet radiation. In the DiamondView, they luminesced bright orange, and seven showed parallel laminated growth structures. The streaked ADR pattern, fluorescence, and growth structures are consistent with synthetic diamonds grown by chemical vapor deposition (CVD).
These 48 synthetic diamonds (0.01-0.27 ct) were grown by the CVD method and then treated to produce their pink color. Photo by H. Kitawaki.
UV-visible spectra showed a broad absorption centered around 500 nm (related to nitrogen-vacancy centers at 575 and 637 nm) that was the cause of the pink color and orange fluorescence. Infrared spectra indicated that all samples were type IIa. Most also showed weak hydrogen-related features, but an absorption at 3123 cm-1 (which has been reported as characteristic of CVD synthetic diamond but annealed out by HPHT treatment) was not detected. In all samples, photoluminescence spectroscopy detected silicon-related defects - which are characteristic of CVD synthetic diamonds - as well as GR1 centers and a 389 nm line, which are related to irradiation.
The nitrogen-vacancy centers were apparently formed by HPHT treatment followed by irradiation and annealing of the nitrogen-containing CVD synthetic diamonds. A combination of gemological and spectroscopic characteristics were used to identify all 48 of these pink melee as treated-color CVD synthetics.  
Article Written By:   
- Hiroshi Kitawaki, Ahmadjan Abduriyim, Jun Kawano, and Makoto Okano
Gemmological Association of All Japan - Zenhokyo, Tokyo

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