|
|
Figure 1. The round brilliants in this ring (average 2.8 mm diameter) proved to be treated-color pink synthetic diamonds. Photo by S. Singbamroong, © Dubai Gemstone Laboratory.
|
Recently, the Dubai Gemstone Laboratory received a yellow metal ring set with 12 pink round brilliants for identification (figure 1). The round brilliants averaged 2.8 mm in diameter and exhibited a saturated color that varied from orangy pink to brownish purplish pink. They gave a positive (diamond) reaction to a thermal conductivity tester.
With strong fiber-optic illumination, nine of the 12 samples showed unevenly distributed weak-to-moderate green luminescence. The reaction to ultraviolet radiation was also striking. When exposed to long-wave UV, all displayed a distinctive weak-to-strong yellowish orange, orange, or orangy red fluorescence, with the same nine samples also showing zones of greenish yellow to green. The reaction to short-wave UV was similar but stronger, and the zoning was more clearly defined (figure 2). In both cases, the green-fluorescing areas showed the cross-shaped, hourglass, or three-armed growth sector patterns that are typical of synthetic diamond. There was no phosphorescence reaction in any of the stones. The DiamondView luminescence images of the nine samples displayed additional distinctive features characteristic of a synthetic.
Microscopic examination revealed metallic inclusions in six of the samples and a cloud of reflective pinpoint inclusions in one; among these were the three samples that did not show the green luminescence zoning mentioned above. Immersed in water and examined with diffused light, the nine samples that did have green zoning showed uneven color distribution, with distinct zones of yellow and pink. This is also a typical feature of synthetic diamond.
|
|
Figure 2. When exposed to short-wave UV radiation, most of the treated synthetic pink diamonds revealed zones of greenish yellow to green over a red background, with cross-shaped, hourglass, and three-arm growth sector patterns. These are typical features of synthetic diamond. Photo by S. Singbamroong, © Dubai Gemstone Laboratory.
|
Due to the size of the synthetic diamonds and the nature of the mounting, it was not possible to perform UV-Vis absorption spectroscopy. However, low-temperature photoluminescence spectra recorded for two samples with a Raman microspectrometer using a 514.5 nm argon laser showed emission peaks at 575 and 637 nm, which are indicative of irradiation and annealing treatment, as well as a 658 nm band due to nickel impurities that is indicative of synthetic origin.
The infrared spectra of two samples revealed features that were a mixture of type Ib, IaA and IaB (with IaA>>IaB, Ia>Ib). They also revealed a peak at 1450 cm-1, additional evidence of irradiation and annealing. EDXRF chemical analysis of two samples revealed the presence of nickel and iron.
On the basis of the color zoning, luminescence characteristics, and chemical/spectroscopic properties, the 12 small round brilliants were identified as treated-color pink synthetic diamonds.
Sutas Singbamroong and Abdalla Abdelqadir Yousif
Dubai Gemstone Laboratory, United Arab Emirates
|
