ADAMAS GEMOLOGICAL LABORATORY publishes gemologically oriented software for the jewelry appraiser, jeweler, or student in gemology or mineralogy. The laboratory also provides technical consulting and jewelry appraisal services to the trade and the public and expert witness services to the legal profession.

FANCY DEEP BROWNISH YELLOWS

HPHT DIAMOND SPECTRA

SAS2000: Developed, Produced And Supported In The USA   Questions, Comments, Product Support
Adamas Gemological Laboratory is proud to introduce to the industry the custom built SAS2000 Spectrophotometer Analysis System for diamond and gemstone evaluation and grading. The SAS2000 provides the most accurate colorimetry available today for diamond color grading, helps determine radiation treatments of diamond, provides better ability than the DeBeer's DiamondSure to detect probable  synthetic diamonds , and replaces the spectroscope for transparent gemstone evaluation.

LABORATORY WARNING

We have been sent a 1.02ct VS2 round brilliant cut fancy colored diamond which had been sent to a major laboratory and received a "Natural Fancy Deep Brownish Yellow" color/origin call, which it turns out is erroneous, because supporting documentation establishes that the diamond in question had been previously HPHT treated.

In talking with the HPHT treater, it was established that the "treatment" didn't take, in other words the stone did not change to the fluorescent yellow green or yellow that was expected and/or desired.  The treater refered to the diamond as a "cape stone of O/P color", however was no evidence of N3 centers in the spectra taken post processing.

There is evidently there is either a class of diamonds which responds to HPHT this way or there is sufficient variability in the processing controls which result in these inert brownish yellows, much to the chagrin of the processor.  These stones may be difficult to class as HPHT treated.

The diamond was inert to SW ultraviolet and had a very very weak LW fluorescence, such that it received an "inert" designation by the grading laboratory.  The grading laboratory apparently did miss an important "clue" of small dark graphitization contained in the surface reaching feather(s) on the pavilion, although the feathers were plotted. I was told that this could be a natural phenomena also.

The grading laboratory also indicated that the stone in question had showed characteristics of hydrogen unter FTIR, but I was unable to obtain a copy of the FTIR plot.

The normalized Vis-NiR spectra, both using liquid nitrogen and at room temperature were not remarkable, as shown below, with the exception of a possible hint of a H2 (986nm) center in the room temperature spectra. These results may give a false sense of the diamond being of natural color origin. Things are changing every day.
 


The (unusual to me) normalized Raman/Photoluminescence spectra shown (at room temperature and using SAS2000 liquid nitrogen immersion {LNIS} techniques) MAY have HPHT diagnostic value.  What was also UNUSUAL in this case was the significant reduction in the visibility of the prominent 657/658 signal seen at room temperature compared with the LNIS spectra on the same diamond.  I welcome any commentary on the interpretation of these data.

I have also heard that similar circumstances as above, where the VisNiR spectra appear normal, exist for some class of orange colored diamond, even after HPHT processing.
 
 

 SAS2000 Spectrophotometer   Questions, Comments, Product Support AD