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TypeIa Diamond
Particular Kind of TypeIa Yellow Diamond The samples used in this study were typeIa yellow diamonds, which characteristically show absorption on 1480cm-1 in FTIR. This absorption on 1480cm-1 was confirmed to emerge when a typeIa natural diamond was HPHT-treated in our joint study with Dr. Collins and other researchers in 2000. However, it was later discovered that some of untreated natural diamonds showed 1480cm-1, so that the existence/absence of this absorption was no longer an indicator for detection of HPHT treatment. Our study on HPHT treatment this time was performed to pursuit identification criterion for typeIa yellow diamond. Change of colour hue Photo 4 shows the stone appearance before and after the treatment. The stones weighed 0.288ct and 0.247ct and were colour-graded as Fancy Yellow and Fancy Light Yellow respectively before the treatment. After they have been HPHT-treated at Sundance Diamonds in US, they turned to be in deeper colour. Their weights after re-cut were 0.285ct and 0.243ct, and colour grade after the treatment Fancy Intense Yellow and Fancy Intense Green Yellow respectively.
External Features Facet surfaces after the treatment are frosty and rough similar to the typeIIb diamond described above. Partly graphitised feathers are also observed under magnification using a microscope. |
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