As previously reported in Rough&Polished publications, scientists in St. Petersburg have used the HPHT method to grow one of world’s largest (70.72 carats) nitrogen-free diamond monocrystals. A 70.72-carat colorless, type IIa stone was used to manufacture a unique colorless fancy-cut diamond of more than 25 carats.
The painstaking work of technologists and cutters of the New Diamond Technology and NPK ALMAZ (Sestroretsk, St. Petersburg) companies has yielded a record HPHT polished diamond of the Radiant Modified Cut shape, weighing 26.26 carats.
According to the assessment of certified and experienced gemologists working at the two companies, the characteristics of this diamond are assessed as: E color, Internally Flawless (IF) clarity.
Images of this diamond taken with the Avrora Diamond Inspector V1 using 220 and 365 nm UV sources show the characteristic yet surprising features of colourless Type IIa HPHT diamonds - greenish-blue phosphorescence at 220 nm excitation and orange phosphorescence at 365 nm excitation.
Galina Semyonova, Editor in Chief of the Russian Bureau, Rough&Polished
