In recent months, the international colored gemstone market trade has been confronted with an influx of rubies, mostly from African sources, that appear to have been heated and then filled with lead glass, the International Colored Gemstone Association (ICA). The organization has issued a “Lab Alert” to inform the jewelry trade.
Several international gemological laboratories have already researched and identified the treatment, and announced that in and of itself the treatment is relatively easy to detect, ICA said in its statement. However, the organization said the gemstone and jewelry trade at large should be informed as to the characteristics of this new treatment.
Henry Hanni of SSEF Swiss Gemological Institute, Basel, Switzerland, says on the basis of his research that it is not difficult to identify rubies that have been heat treated and filled with lead glass.
Summing up the major characteristics of this treatment, Hanni said that to gemologists and researchers it is basically just another “glass recipe.” His lab has been seeing this type of treatment on and off for a few years. Evidently, the people who do gem treatments have discovered that they can use a particular type of glass [of a low melting point]—also called soldering glass because it can be used in industry to solder sheets of glass together—to heat treat and fill fissures in rubies. The application of lead glass of the most recent composition is rather new.
Hanni added that this particular treatment can be done at lower temperatures than other methods involving glass fillers. As a result, this treatment leaves the natural silk inclusions intact, instead of melting them away.
“This may momentarily mislead observers—until they observe telltale gas bubbles and strong purplish blue color flashes,” ICA said in its statement. “That is why the gemstone and jewelry trade should have no difficulty identifying this treatment.”