Linda L. Hines, age 11, of Allentown, for her question:
How do natural and cultured pearls differ?
A thief might bite a pearl before he stole it. If it seemed to have a hard central core he would know it was a cultured pearl and might depart with an empty grab bag, A jewel expert would use several complicated instruments to test a pearl, He could tell whether the pearl was natural or cultured and also just what value the cultured pearl had.
Every pearl, natural or cultured, is built around a central core. In the natural pearl this core is a grain of sand or a tiny foreign body which has invaded the oyster. In the cultured pearl the core is a hard bead placed in the oyster by hand, This brad is usually made of nacres the lovely mother‑ofpearl which lines the oyster shell.
The chemical ingredients are the same in both pearls. The beautiful pearly substance is about 92 per cent carbonate of chalky two per cent water and six per cent gooey material from the oysterts body. Certain it is not these chemical ingredients which give the pearl its value. It is the way the oyster arranges these ingredient. And only an oyster can perform this glamorous trick.
It happens because, the oyster is an excellent housekeeper. He paints his inside walls regularly with very thin layers of pearly nacre. The thin layers of chalky chemicals bend or refract the lights giving the nacre its pearly luster. The nacre is secreted from special cells in the oyster and dries very hard.
Sometimes a grain of sand or a tiny creature invades; the oyster and gets coated with these nacre making sells. The cells go on workings burying the visitor within layers and layers of the nacre. In time, a natural pearl is formed.
Mr. Mikimoto of Japan perfected a way to make oysters create pearls to order. Fine pearl oysters are bred and left to grow in calm bay waters. At the age of three the oysters are gathered and sent to surgery. Each is gently opened and a round brad of nacre is placed inside. The brad has been coated with nacre‑making cells from another oyster. After the surgery, the batch of operated oysters is returned to the calm waters.
In about seven years these oysters have covered the nacre beads with a coat of pearl. An oyster takes much longer than this to build a pearl around, says a grain of sand. What's more, you might have to open thousand oysters to find one natural pearl, Almost every oyster create a cultured pearl after Mr. Mikimotols operation. And the pearl farmer knows just where he has put these oysters.
The fine pearly layers reach almost to the center of the natural pearl. They form only the outer covering of the cultured pearl and may peel away, The lustre of the natural pearl may be more rich and deep and and it will not peel away. However, only an expert can tell which is which only by looking,