To overcome the limitations in current identification techniques for non-bead freshwater cultured pearls(NFC), this study employed X-ray transmission imaging (RTX) and micro-computed tomography (μ-CT) to analyze the internal structures of 45 near-round or baroque NFC, aiming to reveal the correlation between their internal structural characteristics and cultivation origins. The experimental results demonstrate that void structures are universally present in the growth centers of NFC, which can be classified into five morphological types (tiny crack-like voids, tiny rod-like voids, multi-void complex, large crack-like voids, and large rod-like voids). Notably, larger voids were exclusively observed in baroque samples and showed structural similarities to non-bead saltwater cultured pearls ("keshi" pearls), suggesting their formation results from expelled nuclei during cultivation. In contrast, natural saltwater pearls predominantly exhibit compact structures with only 6 % showing central voids, presenting a distinct difference from NFC. While non-bead saltwater cultured pearls display void characteristics overlapping with some freshwater samples, their identification requires comprehensive analysis incorporating additional features. This study not only expands the structural database of NFC but also provides a scientific basis for reliable origin authentication.

Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm−1 absorption intensity was directly proportional to the 3107 cm−1 absorption intensity; the 3143 cm−1 absorption intensity increased with the increase in the 3107 cm−1 absorption intensity, but there was no strict linear relationship between them. The 3143 cm−1 band was not only related to the intensity of the 3107 cm−1 but also related to the value of NC/NA in natural diamonds. When the value of NC/NA was less than one, the 3143 cm−1 band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm−1 defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm−1 and 3107 cm−1 bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds.

China is the world's largest producer of industrial and gem-quality synthetic diamonds, particularly HPHT-grown products. In 2018, production of HPHT synthetic diamonds rose to 18 billion carats of industrial rough and more than 5 million carats of gem-quality rough material. This article summarises the production technology, product quality and output from various companies producing gem-quality HPHT- and CVD-grown synthetic diamonds in China. In recent years, 'hybrid diamonds' (comprised of natural diamond with a CVD overgrowth) have raised identification concerns, and we review differences in the fluorescence, structure and infrared spectrum of the CVD and natural layers. In addition, we briefly discuss diamond-detection devices developed and used in NGTC's laboratories, such as the GV5000. Finally, we compare the gemmological properties of colourless to near-colourless natural and synthetic diamonds.

In October 2017, a natural diamond overgrown by a thick layer of CVD synthetic diamond was identified at the Beijing laboratory of the National Gemstone Testing Center (NGTC). The round-brilliant-cut sample was near-colourless and weighed 0.11 ct. No sign of the overgrowth was observed with magnification. However, DiamondView images showed a distinct boundary in the pavilion separating layers of different luminescence: The upper layer displayed red fluorescence with greenish blue phosphorescence, while the lower portion showed deep blue fluorescence and no phosphorescence. Infrared spectroscopy revealed that the upper layer was type IIa and the lower portion was type Ia. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy recorded an unusual co-existence of the N3 centre at 415 nm together with absorption due to [Si-V](-) defects at 737 nm. The photoluminescence (PL) spectrum confirmed a high level of [Si-V](-) defects. The approximate thickness of the CVD synthetic layer was similar to 740 mu m, which is much thicker than previously reported for such overgrowths. The presence of the N3 centre in the natural diamond layer caused this sample to be passed as natural by various screening instruments. Luminescence imaging is key to identifying such overgrowths, and should be relied upon more heavily in the screening procedures used by gemmological laboratories in the future. (c) 2018 The Gemmological Association of Great Britain

Colourless HPHT-grown synthetic diamonds are becoming more common in the marketplace. The authors recently studied 20 samples weighing 0.06-0.67 ct from a producer located in Jinan, Shandong, China. The 10 crystals showed a combination of cubic and octahedral forms, sometimes with small faces corresponding to {110} and {113}, and the 10 round brilliant cuts had colour grades up to D-E and clarity grades up to VS1. Some of the samples were attracted to a magnet due to their metallic inclusions. They showed very weak anomalous birefringence with low-order interference colours between crossed polarizers. UV-Vis spectra recorded a weak absorption at 270 nm, and infrared spectra indicated that all samples contained variable traces of boron, suggesting that they are mixed type Ib and IIb. DiamondView imaging revealed distinct cuboctahedral growth sectors and produced strong greenish blue phosphorescence. These synthetic diamonds can be reliably identified using a combination of FTIR, UV-Vis, microscopy and luminescence imaging techniques. (C) 2016 The Gemmological Association of Great Britain