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No Reports of Diffusion on Blue Sapphire from Sri Lanka

The Swiss Gemmological Institute (SSEF) and the Gemological Institute of America (GIA) recently reported that through independent studies they have found no evidence of diffusion in a batch of heated blue Sri Lankan sapphires treated by the same source.

The stones in question had undergone a new treatment being used to lighten blue sapphires that were previously too dark to be salable. Reports in the trade media indicated that this treatment of Sri Lankan blue sapphire could have been caused by diffusion.

The process by which the gems are treated is unknown, but the effect is similar to diffusion: The process produces a light blue or colorless surface layer in an otherwise dark blue stone, effectively lightening its color and making it more marketable.

At a panel discussion on beryllium diffusion in sapphire at the 2003 Tucson gem shows, researchers reported that beryllium diffusion had been used to produce the effect in very dark sapphire. The AGTA alert said that no trace of beryllium had been found in any of the sapphires they tested, but they did not rule out diffusion with a different element.

The SSEF recently examined a batch of treated Sri Lankan sapphires and came to this conclusion: "We do not see evidence of diffusion of a foreign element, as in the case of the beryllium treated orange and yellow sapphires."

The SSEF reports that the stones it tested, while immersed, revealed uneven, colorless rims of about one millimeter thick, and that the colorless zones did not completely outline the stones. According to a lab alert from the International Colored Gemstone Association, the SSEF's research team suggests that the colorless rims on the stones' surfaces were caused by a technical oversight in the heating process, during which a minor degree of oxidation occurred -- causing surface de-colorization. The team also says that the colorless zones are not uniform because the stones had been treated as rough and most of the colorless areas had been cut or polished away, an observation first observed by the AGTA.

In light of their recent findings, the SSEF says it will describe sapphires of this nature as "heated" when issuing lab reports.

GIA researchers, when witnessing the sapphire heating process in Sri Lanka, saw no use of any fluxing agents, and the stones they studied later revealed no evidence of diffusion. Despite these findings, they have taken a more cautious approach with this statement: "We cannot state conclusively the role that lattice diffusion plays in this particular color phenomenon or which elements may be involved. However, we are continuing our research into the exact mechanisms responsible for these unusual color concentrations, and will release our findings to the trade as they become available."

This story is an update to: New Treatment Found in Blue Sapphire.

See also:
Bulk Diffusion Sapphire: Links & Past Articles
The GIA
The SSEF
The AGTA
The ICA