From the AG - The challenge of beryllium treated corundum

This news release is a service to the membership that has been prepared by the Editorial Management Committee of The Australian Gemmologist to facilitate rapid dissemination of new gem testing and gemstone related information to the membership, and in particular the GAA’s students. We would welcome feedback from the Divisions and their membership with respect to this initiative. Correspondence should be directed by post to P.O. Box 477, Albany Creek Q 4035; by fax to (07) 3225 0207; or by email to
austgem@gem.org.au.

The problem
Several years have now passed since beryllium treated orange sapphires first appeared in Thai gemstone markets. Following suspicions raised by several international gemmologists - including one Australia gemmologist - co-operative research soon discovered that these padparadscha coloured sapphires were in fact pink sapphires that owed their orange colour to a rim of sapphire of induced yellow colour. The element beryllium was soon discovered to be the main chromophore that created a stable yellow colour centre in the sapphire's crystal structure, after being diffused inwards by the external application of heat. Finding an acceptable descriptive term for this new treatment has proved to be a challenge. Presently bulk diffusion, beryllium bulk diffusion, beryllium diffusion, beryllium heat treatment are some of the terms that have been applied to describe this process. While the term bulk diffusion is the most acceptable scientifically, at this time its use is not universally accepted.

Initial reports indicated that beryllium bulk diffusion treatment could be detected by first immersing the suspect orange sapphire in a fluid of comparable refractive index (di-iodomethane or methylene iodide, RI = 1.742). Subsequent examination of the immersed sapphire, with magnification, allowed observation of a circumferential rim of yellow sapphire surrounding the original pink core of the sapphire. This observation rapidly became less useful following discovery that the yellow colour could be induced throughout the whole sapphire either by decreasing the size of the treated sapphire or by increasing the duration of heat treatment (bulk diffusion).

Other observations that indicated that the sapphire had been heat treated at high temperatures included the presence of:

With respect to these microscope observations it is important to remember that the presence of one or more of these features only indicates that the gem corundum has been heat treated. Their observed presence in no way identifies beryllium bulk diffusion as the cause of any induced colour.

Over recent months the diagnostic usefulness of these features has further decreased, as available evidence suggests that the features attributed to heat treatment are decreasing in severity as it is thought that recent product is being treated at lower temperatures_possibly in association with increased pressures.

Gemmologists in particular, and their clients in general, face additional challenges from beryllium bulk diffusion treatment for this method of heat treatment is now being used to produce a range of attractive, colour stable gem corundums that include ruby, yellow to golden sapphire, blue sapphire, orange (padparadscha) sapphire, and possibly others. Furthermore, this treatment is being performed in countries other than Thailand_ and this includes Australia. Yes … Anakie greens are been converted into very marketable yellow to golden sapphires.

So what can the gemmologist do about this problem?
Unfortunately, the present answer to this question is very little with respect to identification - except be cautious with your identifications, be prepared to refer a suspect stone to a suitably equipped international gem testing laboratory, and keep up to date with ongoing research into this problem.

Certainly, the trained and experienced eye of the trade gemmologist can learn to recognise the unnatural subtleties that this treatment creates in its induced colours. But these colours, such as the 'garnety' colour displayed by some treated ruby, are not positively identifying of this treatment. Also, while the observed presence of an induced symmetrical rim of colour is characteristic of this treatment, it does not prove that beryllium diffusion was the culprit.

It is a fact that the only way the presence of unnatural concentrations of beryllium can be detected, when a suspect ruby or sapphire is submitted for testing, is to submit it to a very expensive chemical analysis that likely will cost more that the stone is worth.

The final indignity for the trade gemmologist occurs once the induced colour has diffused throughout the whole stone. Unfortunately - given the present state of gemmological knowledge - trade gemmologists can not identify this treatment with their day-to-day equipment and skills.

So what can the gemmologist do in response to this challenge?
Basically, he or she must be informed, cautious, and be prepared to add an appropriate qualifier to any identification they may be requested to and are prepared to perform on a suspect ruby or sapphire.

Such a qualifier could be:
“Testing for beryllium bulk diffusion treatment can not be undertaken exclusively by gemmological testing methods and gemmological equipments currently available and used everyday by the trade gemmologists. Therefore, while this ruby/sapphire does not seem to display any visual evidence of beryllium bulk diffusion treatment, the possibility that this may have occurred can not be completely ruled out. Only further laboratory chemical analysis can accurately identify this treatment.”

“While this ruby/sapphire displays no evidence of beryllium bulk diffusion treatment, the possibility that this may have occurred can not be detected by gemmological testing methods that are presently available to trade gemmologists.”

It should remembered that if beryllium bulk diffusion treatment is detected, this can possibly affect the value of the gemstone significantly.

There is no argument that if evidence of beryllium bulk diffusion treatment is noted in a ruby to sapphire then this must be disclosed to a client by the gemmologist. Failure to do so would be considered to represent culpable negligence. However, how to individually handle this ever growing problem remains a problem that the GAA, gemmologists, the trade, and their customers still must resolve.

For the interested reader, the select reference list, below, traces the evolution of this potentially troublesome colour enhancement for gem corundum.