July 7, 2004
Rubies With Glass Treatment Seen
The American Gem Trade Association's Gem Testing Center warns the trade to be aware of a glass treatment in rubies. AGTA-GTC received a 16-ct. ruby at its New York laboratory in June which had been treated by this method, suggesting a new form of glass-filled rubies might be entering the trade. AGTA-GTC says it does not know the prevalence of such a treatment at this time.
AGTA-GTC says its own experience follows an alert by the Gemmological Association of All Japan, which described a filling within ruby fissures that is similar to glass fillings applied to diamonds by companies specializing in the treatment, such as Koss or Yehuda. The treatment is usually performed in diamonds to hide visible fissures or feathers that might detract from the gems' beauty. In colored gemstones, emeralds are also often filled with oils and resins to soften or eliminate the visibility of surface reaching fissures.
AGTA-GTC says its tests confirm GAAJ's ruby findings through optical examination and energy dispersive X-ray fluorescence spectrometer testing. Through the microscope, preferably using dark field illumination, a viewer will see a "flash effect." The flash effect is an optical feature visible when fillers with a given refractive index (such as high leaded glass) are introduced into a medium with a similar refractive index (such as ruby). Seen along the fissures or cleavages in the gem is an interference color that appears and gets stronger or weaker. In some cases color changes as the gem is tilted in different directions. GAAJ describes "an odd blue to purple light effect" within these treated rubies.
Fillings are not entirely new to rubies. There have been descriptions of glass-like substances used to fill pits, voids and fractures in rubies during the cutting process. Other forms of fillers enter these areas during high-temperature treatments. GAAJ says this is the first time high leaded glass and its flash effect was observed.
by Robert Weldon, G.G.