James Capobianco, age 12,, of Brooklyn, N.Y., for his question;
How are pearls formed in oysters?
A natural pearl is made from layers of glossy nacre. This is the material an oyster uses to cover the inside of his shell. A cultured pearl has but a few layers of nacre covering. Nacre is no more than a blend of common limoy chemicals which are dissolved in seawater. But then, a diamond is no more than a crystal of common carbon. Diamonds and pearls are valuable because they are rare and beautiful arrangements of common elements. A perfect, natural pearl is as hard to come by as a diamond ‑ and certainly as beautiful.
Many shellfish make pearls, but only the pearl oyster makes the valuable oriental gem pearl. These oysters enjoy life in certain warm ocean waters. They are relatives of the food oysters that repose on the floors of bays where streams and rivers empty in fresh water. Pearl oysters are found in the:; Persian Gulf, off northern Australia, Japan, the East Indies and the warm western shores of America.
These regal oysters line their shells with the most beautiful nacre of all. Nacre is also called mother‑of‑pearl, which is fair enough since it is the substance used to make pearls. The ingredients are sifted from soawater by the oyster, just as your body sifts the goodness from food. The ocean chemicals are processed and secreted from the oysters special skin. It dries into thin, thin layers of hard, colorless gloss. Layer is added upon layer. As light strikes this nacre, it is refracted, or bent. Its radiant colors are bent as by a prism. This is what gives the translucent glow to mother‑of‑pearl.
If all goes well, an oyster simply covers the inside of his shells with layers and layers of hard smooth nacre. These smooth walls are necessary to protect his soft body. But sometimes a bit of grit, a worm or a parasite gets weded between the wall and the skin. Some of the special cells which secrete the nacre may be trapped around the irritating guest. They continue their work as usual. Only instead of covering the inside walls, they cover the scratchy little invader.
As time, goes on, the bit of foreign matter is buried under layers of smooth, glowing nacre. Once in a great while, the nacre cells form a perfect sphere around the invader and in time a perfect pearl is formed. But most often the pearl is stuck to the shell, or otherwise placed to grow lopsided.
Cultured pearls are started with small beads of shell material placed in the oyster where they will grow round. Their value depends upon the number of pearly layers and this depends upon how long they are left in the oyster. On the surface they have the same beauty as natural pearls made entirely by the oyster. But they do not have the same deep, translucent glow. What's more, their pearly coats may chip and peel away.