Five low-quality Pinctada maxima bead cultured pearls showing dull surface lusters, yellowish brown imperfections, and residual organic-rich features. Photo: Nuttapol Kitdee
Figure 13. Two pieces of P. margaritifera shell before (left) and after (right) bleach treatment using both solution and cream methods, which lightened the samples’ color, especially toward the edge of the larger shell. Photos by Sood Oil (Judy) Chia.
Figure 11. Immersing BA 04 (left), BA 05 (middle), and GIA 01 (right) in acetone, ethanol, and isopropanol, respectively, for six hours did not result in any major color change. Photo by Sood Oil (Judy) Chia.
Figure 10. PL spectra were obtained for two treated samples (BA 06, purple; BA 04, blue) and two naturally colored specimens (N 03, green; N 05, red) using 514 nm laser excitation. The characteristic feature at around 650 nm became less defined in the treated cultured pearls; these samples generally showed a higher overall fluorescence intensity and F/A ratio than their natural counterparts.
Figure 12. Four Tahitian cultured pearls, shown before (left) and after (right) identical bleach treatments using both solution and cream methods, exhibited minimal bodycolor changes. Photos by Sood Oil (Judy) Chia.
Figure 9. PL spectra of shells from Pteria sterna (red), Pteria penguin (green), Pinctada margaritifera (blue), and Pinctada mazatlanica (purple), using 514 nm laser excitation, display the characteristic triple-peak pigment-related pattern found in the shells of these species. This pattern, also found in pearls produced by these mollusks, serves as an identification criterion.
Figure 8. UV-Vis-NIR reflectance spectra are shown for a natural-color pistachio pearl (N 02, blue) and a treated pistachio pearl (BA 06, red). The treatment removed the 495 and 405 nm features.
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