Abstract
The relationship between optical behaviour and microstructure of pearl was studied by laser scanning confocal microscopy, high resolution scanning electron microscopy and atomic force microscopy. There are three optical effects in pearls, namely, the reflection–diffraction effect, a chromatic diffusion halo and the whispering gallery effect. From the structure observation for pearls, we proposed that the first optical effect exhibited by pearls is dominated by the surface diffuse reflection. In addition, the multilayer interference and diffraction have little contribution. With delicate observation for the structure of pearl by an atomic force microscope, it is revealed that the polygon platelets of pearl are not single crystals but nanograins of aragonite in the network of organic matrix, which is responsible for the chromatic diffusion halo. As for the third optical effect, it originates from the stratification structure, which is composed of aragonite platelets. When the light falls on the surface of the pearl, it will travel along the laminations of its structure rather than through the whole pearl, so the rim of the pearl is bright even if no light falls on the surface directly.
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