Gem News International Gems & Gemology, Spring 2016, Vol. 52, No. 1

Large Colorless HPHT Synthetic Gem Diamonds from China

Chinese HPHT-grown synthetic diamonds
Figure 1. A factory in Shandong, China, is producing a large number of colorless HPHT synthetic diamonds for the jewelry industry. These crystals have typical cuboctahedral morphology and weigh up to 3.5 ct. Photo by Jianxin (Jae) Liao.

High-pressure, high-temperature (HPHT) technology for gem diamond synthesis has made rapid progress in the last few years. It is now being used to produce many melee-size diamonds around 2–3 mm in diameter and large colorless single crystals, all with significantly improved quality and growth rate. One Russian company is reportedly growing multiple large, gem-quality colorless diamond crystals in a single run (U.F.S. D’Haenens-Johansson et al., “Large colorless HPHT-grown synthetic gem diamonds from New Diamond Technology,” Fall 2015 G&G, pp. 260–279). Here we report on large diamond crystals manufactured using a similar technology by Jinan Zhongwu New Materials Co. Ltd in Shandong, China.

We visited the Chinese factory in early March 2016 and obtained 50 crystals (figure 1). The crystals were examined using the instrumentation and techniques applied to all diamonds submitted to GIA for grading; all exhibited the typical characteristics of HPHT growth and were identified as synthetic. These were basically colorless, with only a few metallic inclusions observed. These crystals showed typical cuboctahedral morphology, with well-developed {100}, {110}, and {111} growth sectors and a weakly developed {113} sector. The crystals we obtained ranged from about 0.5 to 1.2 ct each. Absorption spectra in the infrared region showed they were type IIa diamond, but trace absorption from boron was detected (2800 cm–1). Detailed gemological and spectroscopic analyses are ongoing and will be reported separately.

According to the manufacturer, large quantities of gem-quality colorless and blue diamonds are produced in this factory, in sizes up to 3.5 ct each. While the total production volume remains unclear, it is undoubtedly significant, and capacity is likely to expand in the near future. This strongly suggests that even more large HPHT synthetic diamonds will be introduced into the jewelry industry.

Wuyi Wang is GIA’s director of research and development. Thomas Moses is GIA’s executive vice president and chief laboratory and research officer.