GIA gemmologist Troy Ardon and senior research scientist Christopher Breeding authored an article published in the organisation’s Gems and Gemology Spring 2017 journal that stated they were “very surprised” to find a H4 defect in a synthetic diamond created using chemical vapour deposition (CVD).
The article noted that a H4 defect was one of the most common defects in natural diamonds, consisting of four nitrogen atoms and two vacancies, and it was the first time the laboratory had identified such a phenomenon in a CVD synthetic stone.
The round, brilliant cut 0.26-carat pink CVD stone was submitted to the GIA’s Carlsbad laboratory in California for a synthetic coloured-diamond grading report, before being returned to the owner with the requested report.
According to the article, nitrogen was the most abundant impurity found in diamond and the H4 defect was very difficult to achieve in synthetic diamond growth or post-growth treatment.
“This diamond was grown using gas that was doped with nitrogen, allowing its incorporation into the diamond lattice as single substitutional nitrogen,” the article read.
“This CVD synthetic diamond had low total nitrogen content and was grown under vacuum and likely irradiated and annealed at atmospheric pressure, making the occurrence of H4 even more puzzling.”
Breeding told Jeweller that while the find was “scientifically interesting”, its discovery did not have an effect on identifying synthetic stones.
“The scientific value of this discovery is that it suggests that a major diamond defect (H4) that was thought to only form from complex aggregated nitrogen impurities that occur in natural diamonds can be formed by a different mechanism,” Breeding explained.
“[However,] all of the known criteria for identifying synthetic diamonds remain valid and we are confident in our ability to separate all synthetic stones from natural diamonds,” he added.
The article concluded is was possible that the H4 defect was created during the irradiation and annealing process; however, it stated “among the many samples GIA has examined, this was the first observation of this defect in a CVD synthetic diamond”.
Unexpected findings
The GIA has announced several “significant” synthetic diamond findings over the past year.
As previously reported by Jeweller in May 2017, a natural diamond with a blue synthetic coating was discovered, the first of its kind the organisation had encountered.
The grading laboratory also identified an undisclosed 5.19-carat CVD synthetic diamond – the largest of its kind reported in the industry – in October 2016. This came a few months after the examination of an emerald cut high pressure, high temperature (HPHT) diamond; the stone was said to have weighed 5.03 carats and was the largest faceted blue synthetic stone the GIA had tested.
When referencing CVD and HPHT technology in relation to the industry, the GIA has previously noted that CVD technology had accelerated in recent years, producing large, high-quality and colourless and near-colourless synthetics. It was also stated in March 2016 that the rapid progress in HPHT technologies would “eventually impact the jewellery industry”.
More reading:
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