Effects of γ-Ray Irradiation on Colour and Fluorescence of Pearls

The colour of cultured pears of P. fucata can be changed by γ-ray irradiation, which has been applied to pearl processing. The effect of γ-ray irradiation on the colour and fluorescence of pearls was investigated experimentally. The experimental results show that a colour change of pearls to bluish-grey is mainly responsible for a decrease in the reflection factor of the nuclei. Furthermore, a significant change in the fluorescence spectra has been observed for pearls and nuclei. These changes are considered to be caused by the degradation of conchiolin contained in the nacre. Fluorescence from pearls is not affected by the nuclei, but the colour of pears is affected. Thus, the fluorescence method is suitable for investigating the effect of γ-ray irradiation on the nacre.