“Ruffles” on a Freshwater Pearl
Surface is one of GIA’s 7 Pearl Value Factors describing the appearance of pearls. Because pearls are a product of nature, it is rather common to find blemishes or irregularities on the surface. However, the “ruffle” pattern exhibited by one particular pearl was fascinating.
The 4.61 ct non-bead cultured freshwater pearl’s surface appeared unusually bumpy to the eye (figure 1). Microscopic examination under fiber-optic light revealed an interesting finding: a rainbow-colored wavy pattern under a translucent surface with no indication of treatment. Surprisingly, these ruffles were not caused by actual blemishes or irregularities on the pearl’s outermost surface, but were formed by interactions between light and the unique nacre platelet arrangement under the pearl’s surface (figure 2).
When light is projected onto a pearl’s surface, iridescence can be observed due to diffraction and interference of white light caused by the layered arrangement of the nacre platelets (E. Fritsch and G.R. Rossman, “An update on color in gems. Part 3: Colors caused by band gaps and physical phenomena,” Summer 1988 G&G, pp. 81–102). This underlying botryoidal feature on the surface may be explained by the special arrangement of nacre platelets that was determined by nature.
While similar features have previously been reported in akoya pearl (Fall 2021 G&G Micro-World, pp. 271–272), this is the author’s first encounter with this intriguing appearance. The presence of these ruffles makes this freshwater pearl worth documenting.
