Synthetic ruby ​​filled with lead glass submitted to the GIA for identification

Gems & Gemology, the quarterly scientific journal of the Gemological Institute of America, in its Spring 2021 issue, reported the startling news of the detection of a lab-grown ruby ​​filled with lead glass, a process typically applied to natural rubies in using a filler material with a refractive index very close to natural rubies, to minimize the occurrence of breakage and improve the clarity of very low quality rubies. The biggest question was why would anyone resort to treating a synthetic ruby ​​with lead glass filling, a process reserved for natural stones, unless of course the synthetic material is also of very poor quality with multiple fractures.

The 3.53 carat lab ruby ​​treated with lead glass filling

The GIA Carlsbad Lab received this ruby ​​for identification and reports that the lab usually receives glass filled natural rubies for identification and this is the second time they have received a glass filled lab grown ruby ​​for identification. The GiA further states that while it is unclear why anyone would bother treating a synthetic ruby ​​with lead glass filling, gemologists should be aware that such material exists commercially. .

Initial investigations of the transparent to semi-transparent mixed-cut oval specimen weighing 3.53 carats showed that it possessed all the gemological properties of natural rubies, such as a refractive index between 1.761 and 1.769, a birefringence of 0.008, a specific gravity of 4.01, a uniaxial optical figure and a characteristic spectrum of rubies seen under a portable spectroscope.

Evidence of lead glass filling of fractures in the stone was provided by its examination under magnification, which showed a network of interconnected fractures with dendritic patterns and coarse flattened gas bubbles and a pronounced blue and orange flash effect everywhere, which indicated that the fractures were filled with lead glass.

Close-up of the internal structure of the synthetic ruby ​​showing trapped gas bubbles in high relief and blue and orange flash effects.  Photomicrograph by Diego Sanchez
Close-up of the internal structure of the synthetic ruby ​​showing trapped gas bubbles in high relief and blue and orange flash effects. Photomicrograph by Diego Sanchez

Since no inclusions have been observed to indicate the natural or synthetic origin of corundum, one must resort to fluorescence studies to establish its origin. The stone exhibits strong red fluorescence in long wave ultraviolet (LWUV) and medium chalky bluish white fluorescence in short wave ultraviolet (SWUV). Chalky SWUV is typical of heated ruby ​​and sapphire, but for synthetic sapphire and ruby ​​it is more difficult to observe diagnostic curved streaks in the stone. In this sample, it was much more difficult, because this effect was combined with interference from filled fractures.

A more powerful SWUV light source would be more effective in such cases, and curved growth lines were observed in the DiamondView as chalky luminescent bands, compelling evidence of the origin of the lab-grown stone.

Curved growth streaks were observed in the stone using the DiamondView, conclusively proving the synthetic origin of the ruby ​​- Image by Forozan Zandi
Curved growth streaks were observed in the stone using the DiamondView, conclusively proving the synthetic origin of the ruby ​​- Image by Forozan Zandi

Lead glass filling in corundum is easily detected with magnification, identifying features being very low relief fractures, flattened and rounded gas bubbles, unfilled areas or voids in fractures and an effect of blue and orange flash. This ruby ​​exhibited an orange and blue flash effect as seen previously, as well as gas bubbles trapped in fractures which provided conclusive evidence of lead filling of fractures in this synthetic ruby.

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