Co-Glass and Sapphire Composites

Posted on February 28, 2013 by Dr. Cigdem Lule, FGA, GG (GIA)

During a December trip to the 2012 GIT Conference in Bangkok, Thailand, the author purchased several blue stones claimed to be (Cobalt) Coglass filled sapphires. General observation seemed to confirm the blue sapphire color with a fairly transparent look. Microscopy during standard gem testing revealed an apparent bright blue filling in the fractures. Flash effect (Figure 1) and contraction bubbles (Figure 2) were also readily apparent. Although the flash effect is weaker than the glass and ruby composites commonly seen in the market, both examples share similar structure. This material was our first experience with the new generation of glass filled and corundum composite material that was reported by the GIT in May of 2012.

Based on these samples, identification of Co-Glass and Sapphire Composite should pose no challenge to trade professionals as long as magnification is used. Contraction bubbles and unusually blue irregular fractures are typical. RI readings can be varied, although those taken of these specimens …

Download the Full Article