Structural characterization of non-bead freshwater cultured pearls using X-ray transmission imaging and...

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.