When melee diamond testing becomes a true challenge, even for our very specialized lab.....

Imagine you receive 1139 colorless diamonds from 0.35 (!) to 3.1 mm, average 0.9 mm, that were pre-screened by all means at another laboratory, and all these are what that lab rejected as very likely synthetics - and now you are supposed to separate them into natural diamonds, HPHT synthetic diamonds, as-grown CVD synthetic diamonds and HPHT synthetic diamonds.... This is what happened here a few weeks before the virus has virtually halted business, and this job has brought even us to our limits.

Fig. 1. The analysis plate with part of the tiny samples that had to be tested at low temperature. Photo: Dr. Thomas Hainschwang.

The stones were tested by our Mega DFI prototype using the 7 different UV excitations availble, at first at room temperature and divided into the different groups, with one additional group called "unclear". Then each group was tested under various UV excitations from 220 to 400nm and 405 nm laser with the DFI at 77K (liquid nitrogen) to ensure that the RT results were accurate, and to assign the "unclear" stones into one of the resolved groups.

Fig. 2. A 0.9 mm HPHT synthetic diamond selected out of the "HPHT parcel" under the Mega DFI prototype at 77K, and the live spectrum on the screen characterized by the 484 nm defect. Note that all diamonds are in the testing plate at the same time, and diamonds for which the spectra are needed selected by microscopic focussing. Photo: Dr. Thomas Hainschwang

Fig. 3. A close-up of the "natural diamond parcel" under the Mega DFI prototype at 77K, under deep UV excitation. Photo: Dr. Thomas Hainschwang

This step resulted in stones that still were unclear, hence a group of really difficult "unclear" diamonds.... now the tricky part here is that you are trying to identify the most challenging extremely low defect diamonds with an average weight of 0.0046 cts, and that the trickiest cases turned out to be the very smallest stones, hence a bunch of about 60 stones of 0.35 to 0.7 mm. These were then tested with the same instrument at 532 nm laser excitation, again in liquid nitrogen... the spectra recorded had to be so excessively accurate in order to identify the tiniest defect traces present, we actually had to saturate the signal of the second order Raman peak for some cases....

Fig. 4. Low temperature (77K) 532 nm laser PL testing of the most problematic diamonds under the Mega DFI prototype. Photo: Dr. Thomas Hainschwang

Fig. 5. A series of 532 nm laser excited PL spectra of some of the most problematic and difficult diamonds between 0.35 and 0.7 mm, all showing how far the spectra had to be pushed to detect any conclusive defects in the diamonds. For som ediamonds the second order Raman was to intense for the detector (not shown). Photo: Dr. Thomas Hainschwang

This task would have been virtually impossible without our very specialized DFI prototype and the experience of Dr. Thomas Hainschwang. Finally every single stone was resolved, resulting in 710 natural diamonds, 408 HPHT synthetic diamonds, 13 as-grown CVD synthetic diamonds and 7 HPHT treated CVD synthetic diamonds.

Fun job but VERY challenging!

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