Gemmology Canada - Special Edition
by Shirley Ford-Bouchard, A.G. (C.I.G.), Winnipeg
"A smooth, rounded, variously tinted nacreous concretion formed as a deposit around a foreign body in the shells of various molluscs and largely used as a gem" - what an ominous description for something so lovely. The unique qualities of the pearl were particularly well described by George Krenz and Charles Stevenson in 1908 in THE B00K 0F THE PEARL (page 305).
"Unlike other gems, the pearl comes to us perfect and beautiful, direct from the hand of nature. Other precious stones receive careful treatment from the lapidary and owe much to his art. The pearl, however, owes nothing to man... It is absolutely a gift of nature, on which man cannot improve. We turn from the brilliant, dazzling ornament of diamonds or emeralds to a necklace of pearls with a sense of relief, and the eye rests upon it with quiet, satisfied repose and is delighted with its modest splendour, its soft gleam, borrowed from its home in the depths of the sea. It seems truly to typify steady and abiding affection, which needs no accessory or adornment to make it more attractive. And there is a purity and sweetness about it which makes it especially suitable for the maiden."
The pearl is the oldest known gem, and for centuries it was considered the most valuable. To the ancient civilizations pearls were a symbol of the moon and had magical powers which could bring prosperity and long life.
All down through history pearls were thought to be divine, more suited to royalty than common folk, but today pearls are often given to the bride on her wedding day because pearls symbolize purity and innocence. In the modern Hindu religion the presentation of an undrilled pearl and its piercing has formed a part of the marriage ceremony.
Pearls, in some cultures, are known for their medicinal qualities. The Chinese use them to cure a large number of ailments, some of which include heart disease, indigestion, and some types of fever.
Pearls are made up mainly of calcium carbonate(CaC03), 84-92%, 4 to 13% other substances, and 3-4% water. Today they are used as a dietary supplement and as an antacid. Also, calcium manganese carbonate is a widely-used heart medicine. The founder of the cultured pearl industry, Mikimoto, stated, " I owe my fine health and long life to the two pearls I have swallowed every morning of my life since I was twenty". He is now 95 years of age.
There are many types of pearls, but the ones we encounter most often in our day-to-day lives are cultured pearls ( both saltwater and freshwater ), seed pearls and imitation pearls.
Very rarely does anyone ever find a natural pearl, also called an Oriental Pearl'. This name is given to any natural pearl found in the West Asia Area. This area encompasses the Red Sea, the Persian Gulf and the Gulf of Mannor off the west coast of Sri Lanka.
Natural pearls are formed when a foreign object enters the shell of a mollusc and irritates the soft mantle tissue within. This irritant can be anything from a minute snail, worm, fish or crab to a particle of shell clay or mud. This object becomes trapped in a depression in the mantle tissue. This depression deepens until a pouch or sac is formed. The sac separates from the rest of the tissue and nacre-secreting cells within the sac secrets nacre over the irritant. This nacre builds up layer by layer. All of this occurs without the intervention of man what-so-ever. Most of these natural pearls are baroque - irregular in shape, neither round or symmetrical. The longer the pearl remains in the mollusc, the more layers of nacre coat it. The pearl grows and so does its chance of becoming baroque. Natural pearls are always of the saltwater variety.
The first thing that comes to mind when we hear the word pearl, is the nearly perfectly round, white to slightly pinkish object we see in jewellery stores and better department stores. These are the cultured pearls that are produced most often by the Akoya oyster from the waters surrounding Japan.
The cultured pearl forms because someone inserts both a piece of mantle from a sacrifice oyster ( so named because this oyster is allowed to die after the tissue samples are taken ) and a nucleus ( which is most often a mother-of-pearl bead ) are inserted into the mollusc. These molluscs are of the species Pinctada ( also known as Meleagrina and Margaritefera ). The nucleus and mantle piece are inserted into a channel which is usually cut in the foot of the mollusc. Often a second incision is made elsewhere in the mantle tissue and another bead is placed therein. This is done to cause a more rapid action within the mollusc.
Only about sixty percent of cultured pearls produced are of saleable quality and of these, only four percent are considered fine quality. Generally, it takes from one to four years to produce saleable pearls, depending on the nacre thickness that is desired.
The colour of pearls is dependent of the colour of the nacre on the inside of the mollusc in which it is grown, the position of the nucleus within the mollusc, the length of growing period and the quality of the water. Also, the colour of the mantle tissue inserted has a direct bearing on the colour of the pearl. If the tissue is yellow, a pearl that is creamy coloured is formed; if the tissue colour is white, the colour of the pearl produced will also be white.
There are a number of methods used to distinguish natural from cultured pearls. Many of these methods are inconclusive and should not be used on their own. Most people gravitate towards the old stand-by - rubbing the pearls against their teeth - but some customers may object if the jeweller performed this not-so-scientific procedure in front of them.
The most reliable methods of separating natural from cultured pearls is a combination of X-radiography and X-ray fluorescence testing procedures.
Freshwater pearls of superior quality also come from Japan; more specifically, Japan's largest lake, Lake Biwa. Lake Biwa was one of the first freshwater culturing sites, but due to pollution, production of these pearls has come to a virtual stand-still.
Freshwater pearls are produced by a variety of clams and mussels. In the Lake Biwa waters, the freshwater clam Hyriopsis Schlegeli is employed. The method of freshwater production differs greatly from saltwater production in that many pearls are produced per mollusc. The mantle is notched in many places and a tiny piece of mantle tissue is placed into each notch. A pearl sac forms around each notch and a baroque pearl grows within each sac and in about three years the pearls are harvested.
Freshwater pearls are also cultivated in China, Scotland and the United states.
Unlike saltwater culturedpearls, the freshwater variety of mussels, the Ikechogai, may be harvested a second, and possibly a third time with up to seventy percent of the mussels re-usable. Unlike the first time when incisions were made, none are required in additional harvesting. The same pearl sacs are allowed to produce again and again. The second time around, the number of pearls produced are fewer and flatter in shape although often times the colour and lustre is better than those of the first harvest. Those pearls produced the third time grow much more slowly and the lustre is generally poorer in quality.
Seed pearls are a bonus and they are all natural. They are formed during the formation of natural or cultured pearls. They normally do not become much larger than about two millimetres and they usually weigh less than 0.06 carat.
Imitation pearls are any beads that bear the slightest resemblance to a natural or cultured pearl. There are mainly three types of imitation pearls found in the marketplace today and are marketed mainly in the United States.
These three types are; mother of pearl, solid glass beads and wax-filled glass beads. To make them more realistic looking, they are dipped into a solution called essence d'orient, sometimes as many as forty times and then dipped into clear cellulose acetate and then into clear cellulose nitrate. These " pearls ", after these steps are completed, are very much like the real thing.
Detecting imitation pearls is not a difficult procedure because solid glass beads are much heavier than either natural or cultured pearls, plastic beads are too light, imitation pearls are too perfectly shaped and they feel smooth when drawn against the teeth.
Most pearls are treated or enhanced in one way or another, whether they be saltwater or freshwater. Saltwater cultured pearls are bleached to even out body colour and non-nucleated freshwater pearls will become whiter if they are soaked in a bleach solution or heated for a period of two to ten hours. It is not advisable to heat-treat the larger nucleated variety. The process of dying the pearl to improve the colour or to change the colour can only be used on drilled pearls because the pearl surface is non-porous. The dye must be introduced through the drill hole. Irradiation is a more seldom used process and is suspected in the coloration of grey or blue pearls, but this practice is hard to prove.
We can see by the information provided in this report that pearls, whether natural or cultured, or saltwater or freshwater, can represent a substantial investment. It would be beneficial to be familiar with the care and cleaning to keep our investment at top value. After all, pearls have a predicted lifespan of from one hundred and fifty to two hundred years if cared-for properly. All pearls, whether natural or cultured, anorganic, which means that they were composed by a living organism. "That is the very essence of the warmth and softness of their glow". For this reason they are not as durable as gemstones produced by the heaving pressure beneath the earth's surface.
Perspiration, cosmetics and perfume can severely damage pearls. Therefore, they should be cleaned in warm soapy water periodically, gently scrubbing individually with a soft brush. A soft brush must be used so as not to scratch the surface of the pearl. Care must be taken to clean well around the drill hole, but do not dip the whole strand into the cleaning solution because water could get into the drill hole and cause the pearl to discolour. Also, if the silk thread becomes overly wet, the dampness can cause deterioration of the silk. All pearls should be knotted to prevent the pearls from rubbing against each other end also, if the strand ever becomes broken, only one pearl may become lost. Any dirt that has become caught around the knots should be removed with a toothpick. Pearls should be dried on a lint-free towel or laying them on an absorbent towel could hasten the drying process. If the pearls are worn frequently, they should be re-strung on a regular basis and they should always be strung on silk. It may deteriorate faster, but it will not attract dirt or grime es quickly and it will not stretch. pearls should never be stored with other jewellery. They should be stored in a moisture-free environment and they should NEVER be stored in a plastic bag.
Pearls should be the last thing that you put on and the first thing that you take off. They should always be wiped on a soft, lint-free cloth before being stored.
When cared for properly, your pearls will be worn proudly by your great-granddaughter.
Richard T, Liddicoat, Handbook of Gem Identification, GIA 1989
Renee Newman, The Pearl Buying Guide, International Jewelry Publications 1992
This Special Issue of Gemmology Canada is published for students of the Canadian Institute of Gemmology and others interested in gemmology. The copy-right for any articles remains with the author. For further information write to the C.I.G., P.O. Box 57010, Vancouver, B.C. V5K 5G6 or phone/fax (604) 530-8569 or e-mail firstname.lastname@example.org
Return to main page of Gemology World