(via ICA Early Warning Flash, No.68, April 5, 1993) GIA GTL writes:
Background
The diamond described herein is a 0.88 carat heat-shaped brilliant that was initially submitted to the GIA Gem Trade Laboratory for grading. During preliminary examination, however, a staff gemologist noted at first appeared to be an extremely low relief fingerprint inclusion containing minute voids. As this would be very atypical for diamond, the stone was brought to the identification and research lab for investigation.
Microscopic features
Examination under magnification using standard darkfield illumination revealed several very transparent, colorless, filled fractures. These all contained minute voids as mentioned above, as well very subtle orange and, to a lesser extent, blue flash effects. Difficulty in detecting these effects was compounded by the very shallow angles of the fractures to the surface of the diamond.
The treatment became more apparent when a pinpoint fiber optic illuminator was used. This lighting technique revealed the extent of the filled breaks, including one very large fracture beneath and nearly parallel to the table. The intense illumination made the flash effects significantly more noticeable, as well as revealing hairline fractures in the filling material. The outlines of the filled areas were also found to be easier to detect when examined in transmitted lighting with a single polarizing filter placed between the microscope’s objectives and the diamond.
Additional testing
Qualitative chemical analysis using energy dispersive X-ray fluorescence detected lead, an element previously detected in diamond fillings, X-radiography further confirmed the presence of the filling in the form of white, X-ray opaque areas on the radiograph.
Discussion
Although the diamond under investigation contained extensive filled fractures, the diagnostic microscopic features of the treatment were quite subtle. These might easily be overlooked if only darkfield illumination were used. It is therefore recommended that additional lighting techniques be used when examining diamonds for possible filled breaks, including pinpoint fiberoptic illumination and polarized light.
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