Читать книгу The Book of the Pearl. The history, art, science, and industry of the queen of gems онлайн

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Cross sections of pearls, magnified 30 diameters

Thin section of mother-of-pearl, magnified, showing sponge borings which traversed the pearl shell

Structure of conch pearl produced by fracturing, magnified 80 diameters

The distinctive characteristic, the great beauty of a true pearl, is its luster or orient, which is a subdued iridescence, rather than the glittering brilliance of the diamond; and unless the shelly growth be lustrous it does not rank as a gem pearl, no matter how perfect its form or beautiful its color. This luster is due to the structural arrangement of the surface as well as to the quality of the material. The nacreous material forming true pearls, and likewise mother-of-pearl, is commonly deposited in irregular tenuous layers, very thin and very small in area compared with the surface of the pearl. These laminæ overlap one another, the surfaces are microscopically crumpled and corrugated, and the edges form serrated outlines. The greater the angle which the laminæ form with the surface, the closer will be these serrated outlines, and where the plane of the exterior lamina is parallel with the plane of the surface the lines are not present. This arrangement causes the waves of light to be reflected from different levels on the surface, just as in a soap bubble, and the minute prisms split the rays up into their colored constituents, producing the chromatic or iridescent effect.