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Lead-glass-filled yellow sapphires.

Lead-glass-filled rubies and blue sapphires have been known for several years and have made a big impact on the jewellery market. Some of the treated rubies display an attractive colour and large size, and are priced inexpensively (McClure et al., 2006; Laurs, 2008). Recently, lead-glass-filled yellow sapphires have appeared in the market. This treated material is available in Chanthaburi, Thailand, and it is being sold to dealers at very low cost, by the kilogram.

In February 2015, our laboratory received a large parcel of some 600 faceted pieces (average ~5 ct each) of yellow sapphires for testing and certification. Our client understood that they were glass-filled, but wanted to be sure that the lot was not mixed with synthetic yellow sapphires containing induced flux feathers. We chose 28 pieces showing various shades of yellow and 'golden' yellow coloration for examination (Figure 31). Viewed with the microscope, they exhibited greenish blue, 'golden' yellow and brown colour flashes along glass-filled fractures (Figure 32), which also contained gas bubbles of various sizes and shapes (Figure 33). These features are typical of lead-glass-filled corundum (e.g. McClure et al., 2006). Other inclusions consisted of fine needles, feathers (Figure 32), tabular brown crystals (Figure 33) and lamellar twinning. Unlike the blue colour concentrations in lead-glass-filled blue sapphires, there was no obvious yellow colour concentration in these samples. EDXRF spectroscopy confirmed that the filler was indeed lead glass. For academic interest, the hydrostatic SG for all 28 pieces was found to be in the range of 4.02-4.04.

Our observations confirmed that this parcel consisted entirely of natural corundum that was filled with colourless lead glass. The starting material used for the treatment probably consisted of pale yellow material of very poor transparency.

Jayshree Panjikar FGA

(jayshreepanjikar@gmail.com)

Pangem Testing Laboratory

Pune, India

References

Laurs B.M., Ed., 2008. Gem News International: Tucson 2008. Gems & Gemology, 44(1), 74-75.

McClure S.F., Smith C.P., Wang W. and Hall M., 2006. Identification and durability of lead glass-filled rubies. Gems & Gemology, 42(1), 22-36, http://dx.doi.org/10.5741/gems.42.1.22.

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Title Annotation:Gem Notes: TREATMENTS
Author:Panjikar, Jayshree
Publication:The Journal of Gemmology
Date:Jun 1, 2015
Words:349
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