Lab Notes Gems & Gemology, Summer 2015, Vol. 51, No. 2

Strong Pinkish Purple Freshwater Bead-Cultured Pearls

Bead-cultured pearl necklace from China
Figure 1. This necklace of freshwater bead-cultured pearls from China displays strong pinkish purple hues with orient. Photo by Sood Oil (Judy) Chia.

Freshwater cultured pearls are known for their wide range of attractive colors, including different combinations of white, orange, pink, and purple hues (S. Akamatsu et al., “The current status of Chinese freshwater cultured pearls,” Summer 2001 G&G, pp. 96–113). Jack Lynch of Sea Hunt Pearls (San Francisco) recently submitted a necklace consisting of 33 strong pinkish purple near-round pearls, ranging from 11.90 to 13.85 mm in diameter (figure 1), to GIA’s New York laboratory. The unusually intense color and large size of the pearls immediately drew our attention. Mr. Lynch indicated that the pearls were farmed in both the Hunan and Hubei provinces of China, over a period of three and a half to four years.

X-ray of Chinese bead-cultured pearl
Figure 2. Real-time X-ray microradiography analysis revealed the round shell bead nucleus used to culture each of the pearls. Photo by Yixin (Jessie) Zhou.

Real-time X-ray microradiography (RTX) analysis revealed that all of the pearls in the necklace were bead cultured and had relatively thick nacre (figure 2). Energy-dispersive X-ray fluorescence (EDXRF) analysis detected a high concentration of manganese, confirming that these pearls were grown in a freshwater environment. Furthermore, Raman spectroscopy verified that their color was natural, with two strong peaks around 1130 and 1510 cm–1 associated with natural polyenic pigments found under 514 nm laser excitation (figure 3), consistent with previous studies (S. Karampelas et al., “Role of polyenes in the coloration of cultured freshwater pearls,” European Journal of Mineralogy, Vol. 21, 2009, pp. 85–97).

Raman spectrum of Chinese bead-cultured pearl
Figure 3. Raman spectroscopic analysis on the pearl’s surface showed two natural polyenic pigment peaks at 1130 and 1510 cm–1.

Earlier Chinese production with large beads resulted in a high mortality rate. We continue to see larger bead-nucleated freshwater cultured pearls, so it appears that the process has greatly improved, either through better techniques or hybrid mollusks (D. Fiske et al., “Continuity and change in Chinese freshwater pearl culture.” Summer 2007 G&G, pp. 138–145). Pearls with larger size, a near-round shape, and intense coloration are highly sought after and more valuable than traditional products. The owner’s inquiries revealed that the pearls were formed under an extremely controlled environment and culturing procedures in mussels that produce the material marketed as “Edison pearls.” This necklace proves that current culturing techniques can achieve a wide range of vibrant hues, providing interesting and unique products for the market.

Yixin (Jessie) Zhou is a staff gemologist, and Chunhui Zhou is research scientist and supervisor of pearl identification, at GIA’s New York laboratory.