GIA Lab Grades Largest (4+ ct) HPHT-Grown Synthetic Diamond Submitted to Date

We publish courtesy of Gems & Gemology eBrief

Authors: Wuyi Wang and Tom Moses

Synthetic diamonds have improved dramatically in recent years. The GIA Laboratory recently examined the largest faceted synthetic diamond ever submitted for testing and grading: a rectangular sample measuring 9.07 x 8.54 x 5.98 mm and weighing 4.09 ct. It was color graded Fancy Vivid yellow-orange and had notably even color distribution (color zoning is common in HPHT-grown synthetic diamonds). Some strings of black pinpoint inclusions were seen with the microscope; the clarity grade was VS₁. DiamondView imaging showed typical HPHT synthetic growth sectors, with patterns of varying intensity and color.

The mid-IR absorption spectrum revealed a high concentration of predominantly A-form nitrogen, as well as isolated nitrogen (weak absorption at 1344 cm^-1) — which was responsible for the yellow-orange color. The UV-Vis absorption spectrum showed a typical pattern for isolated nitrogen (gradual increase in absorption from approximately 570 nm to higher energies), as well as features attributed to a Ni-related defect (793.6 nm) and the H2 defect (986.2 nm).

The predominantly A-form nitrogen and the occurrence of the H2 optical center strongly suggest growth at a relatively high temperature. An advantage to high-temperature synthesis is that it limits the development of growth sectors other than octahedra. As a result, the color appears more evenly distributed.

This sample’s size, clarity, and vivid, evenly distributed yellow-orange color were exceptional and demonstrate continued improvements in the HPHT growth technique.

Wuyi Wang and Tom Moses
GIA Laboratory, New York