Secrets of the pearl

StoryImage( ‘/Images/Story//img-0fppnq2tBa.jpg’, ‘Photo by Dr. Robert Hedeen’, ‘Oysters from the Chesapeake Bay frequently form purple pearls.’);

When you sit down to a plate of oysters on the half shell, your chances of finding a pearl are about one in 5,000. However, when we consider the vast number of these bivalves that are consumed each day, it is not surprising to learn that we annually discover several hundred good-sized pearls when we consume these tasty morsels.

Unfortunately, these gems produced by oysters or clams in our waters are usually of no commercial value, except to a few individuals who collect odd-shaped pearls. When I owned a cottage on the Nanticoke River (a major tributary of the Chesapeake Bay) I was able to tong oysters directly in front of my property. The pearls I frequently found in these mollusks did not, however, conjure up visions of early retirement or a dramatic increase in my bank account.

Almost every type of oyster, clam, and mussel is capable of producing pearls, but only the pearl oyster of tropical seas can manufacture the familiar gem pearls of jeweler’s quality. Pearls of lesser value may be found in certain species of freshwater clams, the most notable example being “The Queen Pearl” taken from a clam in a river in New Jersey. This gem was sold over 100 years ago to Queen Eugenie of France for $25,000.

A covering called the mantle protects the soft interior organs of mollusks. Pearls are formed as protection against irritation caused by a foreign object becoming lodged between the shell and the mantle. Pearls may be likened to biological “bunion pads” and are made up of many concentric layers of nacre that is secreted by the mantle. Nacre is better known as mother- of- pearl, and it may vary in color depending on the aquatic environment. For example, any pearl produced by a Chesapeake Bay oyster will be dullish white or tinged with purple. A pearl produced by pearl oysters of the Far East will usually have a deep white sheen, resulting in a beautiful color.

Most of the pearls we purchase today for the special people in our lives are cultured gems and mainly come from Japan. The Asian pearl farmer starts the process by first producing what is called a seed pearl by inserting a small bit of shell or a grain of sand into a pearl oyster. He then sits back and waits for the oyster to do its thing.

In about a year a nacreous layer approximately one millimeter in thickness has been deposited around the foreign body, and the seed pearl is ready for transplantation into another oyster. An additional period of from three to five years is required for a pearl of marketable size to be produced. It is called cultured pearl, and some people have the idea it is some sort of fake or counterfeit gem. Of course, this is not true as it is genuine pearl made by an oyster, with a little assistance from man.

A typical pearl is made up of about 4% water, 4 – 5% organic matter, and about 92% lime (calcium carbonate). Unlike diamonds, pearls may deteriorate within a relatively short time. Direct sunlight affects their structure, and the acid condition of the human skin acts adversely on them. Valuable strings of pearls that are frequently worn should be sent to a jeweler each year for cleaning and rehabilitation.

Many people are unaware that the scales of fishes contain actual color cells or small crystals that add color to the fish as a result of the refraction of light. Years ago it was discovered that the shiny material from fish scales would give beads a luster quite similar to that of natural pearls when it was applied to them. This discovery was an important factor in establishing the costume jewelry industry. The shiny material used to make imitation pearls is called pearl essence, and it is derived by a special treatment of the fish scales that renders out the color producing crystals.

After purification, the pearl essence is mixed with various other things into which beads are dipped and allowed to dry. The quality of an imitation pearl depends on the kind of bead used and the number of times it is dipped into the pearl essence. Some imitation pearls are so realistic it takes an expert to determine if they are the real thing or not.

Whether real or imitation, a string of perfectly matched pearls around a lady’s neck is, in my opinion, the pinnacle of feminine elegance.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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