AGTA GTC's Laboratory Update for June 23, 2006

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AGTA GTC Adds LIBS to its Testing Arsenal
Paraíba redux

AGTA GTC Adds LIBS to its Testing Arsenal

by Richard W. Hughes, Garry Du Toit, Riccardo Befi & John Koivula

Laser-Induced Breakdown Spectroscopy (LIBS) is a technique that brings the cost of beryllium testing in corundum down to reasonable levels.

Also known as Laser Spark Spectroscopy (LASS) or Laser-Induced Plasma Spectroscopy (LIPS), this technique was first developed at Los Alamos National Laboratories and involves focusing a laser pulse onto a surface. The energy from the pulse heats, vaporizes, atomizes and then ionizes the material on the surface, resulting in a small, hot plasma. The atoms and ions in the plasma emit light which is then detected. The unique spectral signatures allow elements in the plasma to be identified.

Diagram of LIBS equipment

Schematic diagram of a Laser-Induced Breakdown Spectroscopy (LIBS) system. Graphic courtesy of Applied Photonics Ltd, www.appliedphotonics.co.uk; used with permission. Applied Photonics specializes in LIBS applications.

Why LIBS matters

In mid-2001, unusual orange sapphires began appearing in Thai gem markets. It was later proven that these stones were actually pink sapphires with an artificially-colored rim created by diffusing beryllium into the stone.

By itself, the beryllium creates a yellow color through a trapped-hole color center. Just a few parts per million of beryllium are enough to produce a significant alteration of color in many specimens. Put this yellow on a pink stone and you get orange. In addition, beryllium can be used to lighten the color of darker blue sapphires.

In the case of some orange sapphires, such as the stone pictured below, immersion is enough to unmask the fraud. But in others, the beryllium penetrates entirely through the gem, making positive identification impossible even for sophisticated gem labs. Such stones previously had to be sent out for expensive SIMS or LA-ICP-MS analyses, tests costing hundreds of dollars per stone.

Enter LIBS. LIBS equipment costs approximately $75,000–90,000 per unit, as opposed to the $300,000+ of LA-ICP-MS or $750,000+ for SIMS. This puts LIBS within reach of many major gem labs, and will translate into more affordable gem testing. This breakthrough should keep the gemologists at least temporarily ahead of those seeking to pass off beryllium-treated rubies and sapphires as something else.

Orange rim surrounding a pink core in a beryllium-treated orange sapphire from Madagascar. The color rim is visible when the gem is immersed in di-iodomethane and is evidence of a treatment. In stones where the beryllium penetrates all the way through the gem, detection is extremely difficult without sophisticated chemical analysis.

Just a few parts per million of beryllium can alter the color of a gem. LIBS promises to dramatically reduce the cost of unmasking this treatment. Photo: Richard Hughes/Pala International; used with permission

LIBS sensitivity for light elements such as beryllium and lithium can be accurate down to the 2–3 parts-per-million (ppm) level. The caveat, though, is that calibration standards for each substance being tested must be created. Thus, for accurate testing of beryllium levels in corundum, calibration standards of known levels of beryllium in corundum would need to be prepared.

Within the past few years, applications for LIBS have exploded. Indeed, prototype LIBS units are even being fit into backpacks for landmine detection, helping soldiers distinguish mines from ordinary metal.

Henry Hänni's Swiss Gemmological Institute (SSEF) was the first gemological lab to announce LIBS testing for beryllium in corundum. In the summer of 2003, the SSEF's Dr. Michael Krzemnicki came across a reference to the LIBS technique on the internet. Hänni had previously been involved in making spectrographs of rocks using light arcs, a similar but more primitive technique. Following Krzemnicki's discovery of LIBS on the internet, he and Hänni began investigating it as a possible solution to the beryllium problem. By January 2004, they were convinced of the technique's viability, but it took some hunting to find a unit suitable for gem testing.

In the case of gem testing, important considerations are:

Ability to detect beryllium down to the 2–3 ppm level
A laser that will leave the smallest possible mark on the stone

The AGTA GTC recently purchased a LIBS unit, through a generous grant provided by the JCK Group, with installation and training provided by SSEF's Michael Krzemnicki. The addition of in-house LIBS testing at the AGTA GTC will give us yet another crucial tool in the ongoing battle to keep up with ever-more sophisticated gem treatments.

LIBS testing at the AGTA GTC

The AGTA GTC's Garry Du Toit testing a specimen using the new LIBS unit recently acquired at the lab. Photo: Riccardo Befi/AGTA GTC

sapphire with beryllium

Sapphire, no beryllium

Laser-Induced Breakdown Spectra (LIBS) of both beryllium treated and untreated sapphires. Graphics courtesy of Applied Photonics Ltd, www.appliedphotonics.co.uk; used with permission. Applied Photonics specializes in LIBS applications.

LIBS spots on the surface

As shown in the pink sapphire above, the LIBS laser leaves small circular depressions on the surface of the sample tested. These are generally visible only under magnification and are easily removed by repolishing. The irregular black marks are due to imperfect polishing prior to the LIBS testing. Photo: John Koivula/AGTA GTC; approx. 30x magnification.

Keystone Fee Structure for the LIBS Testing at the AGTA GTC

Keystone fees for LIBS testing for will be as follows:

$100 (members) or $120 (nonmembers) when the testing is performed as part of an AGTA GTC Identification or Origin Report
$300 (members) or $350 (nonmembers) for the first stone when the LIBS testing is not associated with an AGTA GTC Identification or Origin Report; subsequent tests are $100 (members) or $120 (nonmembers) per stone when stones are submitted together.

Feel free to contact us for more information at 212-752-1717.

Paraíba redux

On May 18th, 2006 the AGTA Gemological Testing Center announced a new policy regarding the issuance of gemstone reports on copper-bearing tourmalines (see The Question of Paraíba). This new policy was the subject of debate at our June membership meeting held at the JCK Las Vegas Show. The AGTA Board of Directors clearly heard at the membership meeting that there were significant concerns among some members about the decision to issue the reports as planned. During the post-show Board of Directors meeting the Board voted to suspend the issuance of these reports and to refer the matter to the soon-to-be-seated AGTA GTC Board of Governors.

AGTA GTC Board of Governors

The AGTA Board of Directors is currently reviewing the Roles and Responsibilities documents that apply to the Board of Governors as well as developing a clear and precise set of bylaws. As soon as this is done we will begin to contact those people who have been suggested as candidates. This list of names has been developed through input from AGTA members, Board members and AGTA staff. Our intention is to have this process completed and a new board seated in a matter of weeks.

As with any issue that is addressed by the Board of Directors, comments from the membership are welcome and encouraged. If you would like to submit written comments on this please email them to info@agta.org or mail them to our office at 3030 LBJ Freeway, Suite 840, Dallas, TX 75234.