著者

和田 浩爾

出版者

宝石学会(日本)

雑誌

宝石学会誌 (ISSN:03855090)

巻号頁・発行日

vol.10, no.4, pp.3-11, 1983

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The spectral characteristics of pearls produced by the different species of marine and freshwater bivalved molluscs were examined by Jewel Color Duble-beam Spectrophotometer. The color of pearls appeared to arise from (1) the interference of the light reflected at the external face of pearls and also at each of the boundaries between the crystal layers consisting of the nacre, (2) the absorbing material of light in the nacre, and (3) the dark organic material contained in pearls. The interference color observed in pearls is variable according to the size, shape, orientation and ordering of crystallites in the crystal layers and exhibits the characteristic iridescence of silver white to pink. The spectrophotometric reflectances of the iridescence were similar to each other between the pearls produced by Pinctada maxima, Pinctada margaritifera and Pteria penguin. We will notice that the major absorbing material is the pigment secreted by the epithelial cells of the pearl sac derived from the mantle epithelium. The color impression of pearls was closely connected with the characteristic pigment in the different species of bivalves, e. g. yellow for Pinctada fucata and P. maxima, black for P. margaritifera, brown for P. penguin, orange pink for Hyriopsis schlegeli, and violet pink for Anodonta calypigos. In the black pearls of P. margaritifera and the brown pearls of P. penguin, the reflection curves had respectively the special absorption bands, probably caused by the characteristic pigment contained in each pearl. The color impression of pearls including the dark organic material was dark and pale blue, and did not differ between the different species of bivalves in the spectrophotometric reflectance. The organic material seems to be composed of anomalous secretions and debris of cells.