[OPTICAL REVIEW Vol. 20, No. 1 (2013) 50-58]
© 2013 The Japan Society of Applied Physics

Optical Measurement of Interference Color of Pearls and Its Relation to Subjective Quality

Toshihiro TOYOTA1,2* and Shigeki NAKAUCHI2

1Industrial Research Institute of Shizuoka Prefecture, Shizuoka 421-1298, Japan
2Department of Computer Science and Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan

(Received June 28, 2012; Accepted November 9, 2012)

Quality evaluation of pearls has been traditionally performed by well-trained experts with the naked eye. Among several characteristics, interference color is a key factor for determining pearl quality. The interference color largely stems from the structure of the pearl's nacre. In the present study, a method for the optical measurement of the interference color and the determination of its relation to the subjective quality of pearl from the spectral characteristics of light transmitted through the pearl is proposed. The spectral characteristics of the interference colors showed a clear dependence on the subjective quality. To quantify and visualize pearl quality, the wavelength of the interference color that shows a high correlation with subjective quality was selected. A validation test with another set of pearls confirmed that the results of the proposed method were highly correlated with those of expert visual evaluation.

Key words: pearl, interference color, optical measurement, subjective quality

*E-mail address: toyota@iri.pref.shizuoka.jp