Glass filled Rubies

This article is courtesy of AGTA/GTC and was published 01-10-08

Glass-filled Rubies More Common in US Market
Over the past few months, glass-filled rubies have become more prevalent in the US market, with increasing amounts of glass seen in certain specimens. In one specimen seen in Thailand, glass appears to form a significant portion of the specimen, raising the question of whether or not the piece could even be considered to be Ruby.

An additional factor in these is the lead (Pb) content of the glass. This could possibly pose a health risk for jewelers working with the gemstones.

The AGTA GTC currently describes glass-filled rubies in the following fashion:

Enhancement:

Indications of heating, TE
  Significant clarity modification, F3, C21
Species: NATURAL CORUNDUM
Variety:  Ruby
Comments: 1A lead glass has been identified as the filler. Lead glass filler may be unstable to elevated temperatures and to chemical agents. Special care shall be taken when repairing jewelry items set with lead glass filled corundum.  This report has been prepared in accordance with the standardized language and criteria set out by the Laboratory Manual Harmonization Committee (LMHC); see reverse.
Gas bubbles in glass filled ruby
A gas bubble floats within a glass-filled area of a glass-filled Ruby. Note the significant undercutting of the softer glass areas. Photo: R.W. Hughes
Glass-filled ruby
This Ruby is riddled with glass-filled fractures. Photo: Lore Kiefert
Damage to glass in glass-filled ruby
Resizing the ring in which this gemstone was once mounted damaged the glass filling in the fissures of this treated Ruby. Photo: Lore Kiefert
Surface of glass-filled ruby
Glass-filled Ruby with large amounts of glass present. The glass has a higher luster than the corundum, due to the Pb content. Photo: Lore Kiefert