Large Freshwater Cultured Pearls with Atypical Bead Nuclei
Freshwater cultured pearls are known for their wide range of attractive colors, including different combinations of white, orange, pink, and purple hues. In the past decade, round or near-round freshwater bead cultured pearls of large size, commonly called “Edison” pearls in the trade, have gained popularity (Summer 2015 Lab Notes, pp. 179–181; C. Zhou et al., “Detection of color treatment and optical brightening in Chinese freshwater ‘Edison’ pearls,” Summer 2021 G&G, pp. 124–134). Recently, two necklaces consisting of large pearls of mostly orangy pink to purplish pink colors (figure 1), ranging in size from 15.40 to 17.42 × 16.70 mm and from 18.00 to 19.96 × 19.06 mm, were submitted to GIA’s New York laboratory. The strands caught our attention for their size and intense colors, as well as the growth features found inside these pearls.
Real-time X-ray microradiography (RTX) revealed that all the pearls were bead cultured—but not with the shell bead nuclei typically used for cultured pearls. Instead, a more X-ray transparent material with a distinct outline and near-round shape was found inside them (figure 2). The material appeared porous and nonuniform and did not resemble the “mud-like” material found in “soufflé” freshwater cultured pearls previously studied (Spring 2010 Gem News International, pp. 61–63). However, the exact nature of this material could not be determined. Energy-dispersive X-ray fluorescence analysis of their trace elemental concentrations (such as manganese and strontium) confirmed that the pearls were grown in a freshwater environment. Furthermore, Raman spectroscopy using 514 nm laser excitation indicated that their colors were natural, with two strong peaks around 1125 and 1510 cm–1 associated with natural polyenic pigment.
Cultured freshwater pearls with large size, near-round shape, and intense coloration are highly sought after and more valuable than traditional freshwater cultured pearls. These large freshwater cultured pearls are especially noteworthy because of the unique bead nuclei used during the culturing process, which suggests that culturing techniques are continuously evolving, resulting in higher-quality products.
