THE AUSTRALIAN GEMMOLOGIST | True Identity – a Colourless Conundrum
True Identity – a Colourless Conundrum
Figure 1. The gold necklace with four colourless gemstones that was presented for valuation.
Recently, a piece of jewellery came across my desk for valuation. Although unstamped, it is a high carat yellow gold (as revealed by acid tests), collier-style neck chain with four colourless round gemstones bezel set at the front (Figure 1).
Testing Process
To identify colourless gemstones, I first screen with a Dr Watson. This is a box-like device that detects synthetic diamond using pulses of LWUV and SWUV radiation. It can test multi-stone pieces of jewellery at once with results recorded, via your phone’s camera, into the manufacturer’s proprietary app. A synthetic diamond, identified with almost 100% certainty, is coloured red on a composite image. This test does not identify diamond imitants (simulants) or composite stones.
Another device, the Gemlogis, is a handheld probe that has two distinct nodes: a traditional thermal probe followed by a second probe that uses UV reactions to identify gem materials. To use this device, you first test the stone’s table or pavilion with the thermal probe to separate colourless gemstones into diamond and/or moissanite, or an imitant such as cubic zirconia. The second test uses UV to identify whether the stone is moissanite, or reconfirm synthetic or earth-mined diamond. Finally, visual examination with a 10x loupe confirms the identity of the gem material as moissanite, diamond or a simulant.
The Stones
Of the four colourless gemstones, the two smaller stones (2.5mm) were identified as natural diamonds. They reacted positively to the diamond thermal probe and gave medium to strong blue fluorescence under LWUV (as did the larger stones; Figure 2). Under 10x magnification, they showed sharp facet edges with no abrasion, had diamond-looking inclusions (carbon spots and feathers), and passed tests using Gemlogis and Dr Watson devices.
The two larger gemstones (approximately 4mm) had a milky appearance which was apparent with the naked eye (see Figure 1). This effect was more than you would generally observe and was not due to the medium-strong LWUV fluorescence. Interestingly, when observed under LWUV, the diamonds appeared to have a patchiness along the facet edges (Figure 2). The SWUV reaction was faint or inert. The test results under LWUV, Dr Watson and Gemlogis showed the gemstones to be natural diamond. But when viewed under a 10x loupe, then under the microscope, things started to get weird.
Figure 2. The four colourless stones showing medium to strong blue fluorescence under LWUV, typical of natural diamonds.
The milkiness originated partly from within the gemstone, and partly from the surface. Both larger gemstones showed a patchy, frosted effect like they had been sputter-coated. They also had abraded and rounded facet edges that were not well aligned. Added to that were some strange surface-reaching pits with heavy black inclusions at the bottom (Figure 3). Examination under the microscope showed that the milky effect was partially banded in two directions at 90° (Figure 4, blue arrows), and there was a series of triangular arrowhead inclusions that were aligned at 45° to the banding (two of their edges are parallel to the banding; Figure 4, green arrow). There were also some rectangular patches in the milkiness (Figure 4, red arrow). There was no evidence of double refraction of the pavilion facet edges or culet from any angle, thus ruling out moissanite or another doubly refracting material.
I repeated the thermal test and UV test combination on the crown and pavilion with the Gemlogis. Each time, results showed the stone to be earth-mined diamond.
So, with this information I was left trying to work out what I was looking at. Positive thermal tests and LWUV fluorescence indicate natural diamond, but the inclusions and surface features were not consistent with any natural diamond I have seen.
My best guess is that the gemstones are not diamonds but perhaps diamond-coated CZ, which I have heard of occurring in the industry. However, CZ often fluoresces yellow, stronger under SWUV and is inert or gives faint fluorescence under LWUV. CVD-created diamonds, and CVD-coating, also usually fluoresce yellow. It is possible that a fine coating of CVD may not create sufficient fluorescence for the detectors to identify.
I open the discussion to readers of The Australian Gemmologist. Can you help with this conundrum? Does anyone know what these gem materials are?
Figure 3. One of the larger diamonds showing milkiness, pits with black inclusions, and rounded and abraded facet edges.
Figure 4. Higher magnification of the diamond shown in Figure 3. The two directions of banding (blue arrows), arrow head inclusions (green arrow) and the rectangular patch (red arrrow) are indicated.
The Valuation
And the valuation? I valued the necklace and priced the unknown larger stones at a nominal value of $50 because I was satisfied they were not diamonds, and, in the slim event that they were diamonds, they were very poor quality and not worth much more than $50. The origin of the necklace is unknown and merely adds to the mystery.
All photos courtesy of the author.