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AGL IDENTIFIES IRRADIATED COLOMBIAN EMERALDS

posted Jan 12, 2012, 6:44 PM by Alex Barcados

NEW YORK:  3 January 2012 Recently American Gemological Laboratories (AGL) has identified Colombian emeralds that have undergone an irradiation treatment. This represents the first emeralds that have been submitted to the laboratory by the trade, which we have identified as being irradiated. Christopher P. Smith, President of AGL described (figure 1).

 

The laboratory had been hearing comments in the trade over the past several months, from wholesalers dealing in Colombian emeralds, that irradiation was reportedly being used as a method to improve the color of certain Colombian emeralds. However no stones had been detected by AGL and other labs until recently.

 

“Nearly 20 years ago, irradiation was shown to be able to modify the color of natural and synthetic emeralds, Smith added. “However we did not see this form of emerald treatment being used widely in the trade. See Schmetzer, 1993.

 

Although the color appearance is slightly unusual for a typical Colombian emerald, the color alone  is  not  a  good  means  to  distinguish  these  treated  gems.  In  addition,  the  various microscopic features of fluid inclusions, mineral inclusions, color zoning and internal growth structures were not helpful in identifying these irradiated emeralds.

 

Spectroscopy  in  the  ultraviolet  region  of  the  spectrum  has  been  shown  to  be  the  most effective  means of identifying  this treatment  (figure 2). Irradiation  may produce  different types of defect centers that absorb in the UV region of the spectrum that may be traced with an appropriate spectrometer.

 

Interestingly, we also noted that these emeralds had been clarity enhanced by introducing a polymer-type resin into fissures to reduce their visibility. Smith noted (figure 3). So these particular  gemstones  had  the  standard  emerald  enhancement  of  clarity,  as  well  as  an additional enhancement of irradiation.

 

Presently it is unknown how much irradiated emerald may be in the marketplace however it is important for suppliers to be aware and for gemologists and laboratories to be on the look- out for this treatment.

 

References:

Schmetzer  K.  (1993)  Radiation  induced  colour  change  in  natural  and  synthetic  emerald.

Journal of Gemmology, Vol 23, No. 5, pp. 288-293.

 

 

Figure 1: Recently, AGL has detected Colombian emeralds that have undergone an irradiation treatment. Depending on the type of irradiation used and the particular defect centers created, the improved color may be stable to light and heat or unstable, which over time will fade. Photograph by Bilal Mahmood.

 

 

 

 

 










Figure 2: In absorbance, the ultraviolet (UV) region of the spectrum for emeralds typically possesses a trough of transmission however irradiation increases the UV absorption. Shown here for comparison is a natural-color (blue trace) and an irradiated (purple trace) Colombian emerald. The light gray area in the UV region of the spectrum highlights the spectral difference that distinguishes this treatment. For the unstable induced color centers heat and/or light will remove the UV absorption causing the emerald to revert back to its original color.


 

  

Figure 3: In addition to being irradiated, these emeralds had been clarity enhanced by filling open fissures with a polymer- type resin. Shown here is the characteristic orange flash effect seen along a filled fissure. 32x, photomicrograph by Christopher P. Smith.

 

 

 

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About American Gemological  Laboratories

American Gemological Laboratories (AGL) is the United States most widely known and

respected colored stone gem identification and quality grading laboratory.  It was founded in

1977 and became the first gemological laboratory in the US to provide quality grading as

well as country-of-origin determinations for colored stones. AGL has become an iconic brand for uncompromised standards and excellence in gemstone reporting (www.aglgemlab.com).

 

 

Contacts:

 

Christopher P. Smith, President chsmith@aglgemlab.com


580 Fifth Avenue, Suite 706 New York, NY 10036 212.704.0727 agl@aglgemlab.com

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