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

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The yield of Pinna pearls is very small. A few are obtained from the Mediterranean, especially on the Adriatic coast. These are usually rose-tinted or reddish in color, but of diminished orient, and inferior in size. Pinna pearls are also reported from the Isle of Pines and from New Caledonia, where they are commonly very dark, almost black in color.

The window-glass shell (Placuna placenta), the vitre chinoise of some writers, yields a few small, irregularly shaped pearls of a dull leaden color. It occurs in the inshore waters of the Indian and the southwestern Pacific oceans; fisheries are prosecuted in Tablegram Lake, near Trincomali, on the northeast coast of Ceylon; on the coast of Borneo, especially at Pados Bay, and to a less extent in some other localities. This mollusk is quite distinct from the true pearl-oyster, and in adult life is devoid of the byssus, living on the muddy bottom of the shallow waters. The shell is almost circular, the right valve is quite flat, and the left only slightly convex. It is remarkable for its transparency, especially in the first year of growth, when the beating of the heart of the mollusk is visible through it. Reaching maturity in about two years, the shell becomes white and translucent, resembling pressed isinglass somewhat in its texture. It then measures about six or seven inches in length, and nearly the same in width. The outside is rough; the interior is glazed over and has a subdued pearly luster. It is so thin and transparent that with a strong light very coarse print can be read through it. It is commonly used in the East Indies as a substitute for glass in windows, admitting a soft mellow light into the room. For this purpose it is usually cut into small rectangular or diamond-shaped pieces, about five or six square inches in area, and these are inserted into sash frames. It forms a good economical substitute for glass, not only in windows of native residences, but also in lanterns and the like.