Valuable pearls occur in the wild, but they are very rare. Cultured or farmed pearls make up the majority of those that are currently sold. Pearls from the sea are valued more highly than freshwater pearls. Imitation or fake pearls are also widely sold in inexpensive jewelry, but the quality of the iridescence is usually very poor, and generally speaking, fake pearls are usually quite easy to distinguish from the real thing. Pearls have been harvested, or more recently cultivated, primarily for use in jewelry, but in the past they were also stitched onto lavish clothing, as worn, for example, by royalty. Pearls have also been crushed and used in cosmetics, medicines, or in paint formulations.
In several European languages, the word “pearl” is synonymous with “bead”, which can lead to confusion during translation.
Definition of a Pearl
Almost any shelled mollusk can, by natural processes, produce some kind of “pearl” when an irritating microscopic object becomes trapped within the mollusk’s mantle folds, but the great majority of these “pearls” are not valued as gemstones. Nacreous pearls, the best-known and most commercially- significant pearls, are primarily produced by two groups of molluscan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell.
A “natural pearl” is one that forms without any human intervention at all, in the wild, and is very rare. Many hundreds of pearl oysters or pearl mussels have to be gathered and opened, and thus killed, in order to find even one wild pearl, and for many centuries that was the only way pearls were obtained. This was the main reason why pearls fetched such extraordinary prices in the past. A cultured pearl, on the other hand, is one that has been formed on a pearl farm. In modern times however, almost all the pearls for sale were formed with the aid of human pearl farmers. The great majority of pearls on the market are cultured pearls.
One family of nacreous pearl bivalves, the pearl oysters, lives in the sea while the other, very different group of bivalves live in freshwater; these are the river mussels such as the freshwater pearl mussel. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain (but by no means all) species of freshwater mussels in the order Unionida, the families Unionidae and Margaritiferidae.
The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. The thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface.
In addition, pearls (especially cultured freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black.
Freshwater and Saltwater Pearls
Freshwater and saltwater pearls may sometimes look quite similar, but they come from very different sources. Natural freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland: see the freshwater pearl mussel. However, most freshwater cultured pearls sold today come from China.
Saltwater pearls grow within pearl oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.
Creation of a Pearl
The difference between natural and cultured pearls focuses on whether the pearl was created spontaneously by nature — without human intervention — or with human aid. Pearls are formed inside the shell of certain mollusks: as a defense mechanism to a potentially threatening irritant such as a parasite inside its shell, the mollusk creates a pearl to seal off the irritation. The mantle of the mollusk deposits layers of calcium carbonate (CaCO3) in the form of the mineral aragonite or a mixture of aragonite and calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. The combination of aragonite and conchiolin is called nacre, which makes up mother-of-pearl. The commonly held belief that a grain of sand acts as the irritant is in fact rarely the case. Typical stimuli include organic material, parasites, or even damage that displaces mantle tissue to another part of the animal’s body. These small particles or organisms enter the animal when the shell valves are open for feeding or respiration. In cultured pearls, the irritant is typically a cut piece of the mantle epithelium, together with processed shell beads, the combination of which the animal accepts into its body.
Natural pearls are nearly 100% calcium carbonate and conchiolin. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk, and settles inside the shell. The mollusk, being irritated by the intruder, secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare.
Value of a Natural Pearl
Quality natural pearls are very rare jewels. The actual value of a natural pearl is determined in the same way as it would be for other “precious” gems. The valuation factors include size, shape, quality of surface, orient and luster.
Single natural pearls are often sold as a collector’s item, or set as centerpieces in unique jewelry. Very few matched strands of natural pearls exist, and those that do often sell for hundreds of thousands of dollars. Yachtsman and financier Cartier purchased the landmark Cartier store on Fifth Avenue in New York for $100 cash and a double strand of matched natural pearls valued at $1 million.
Origin of a Natural Pearl
Previously natural pearls were found in many parts of the world. Present day natural pearling is confined mostly to seas off Bahrain. Australia also has one of the world’s last remaining fleets of pearl diving ships. Australian pearl divers dive for south sea pearl oysters to be used in the cultured south sea pearl industry. The catch of pearl oysters is similar to the numbers of oysters taken during the natural pearl days. Hence significant numbers of natural pearls are still found in the Australian Indian Ocean waters from wild oysters. X-Ray examination is required to positively verify natural pearls found today.
Cultured pearls (nucleated and non-nucleated or tissue nucleated cultured pearls) and imitation pearls can be distinguished from natural pearls by X-ray examination. Nucleated cultured pearls are often ‘pre-formed’ as they tend to follow the shape of the implanted shell bead nucleus. Once the pre-formed beads are inserted into the oyster, it secretes a few layers of nacre around the outside surface of the implant before it is removed after six months or more. It is the nacre that gives pearls their beautiful luster and color.
When a nucleated cultured pearl is X-rayed, it reveals a different structure to that of a natural pearl. A cultured pearl shows a solid center with no concentric growth rings, whereas a natural pearl shows a series of concentric growth rings.
A well equipped gem testing laboratory (e.g. SSEF, Guebelin, GIA, AGTA) is able to distinguish natural pearls from cultured pearls by using a gemological x-ray in order to examine the center of a pearl. With an x-ray it is possible to see the growth rings of the pearl, where the layers of calcium carbonate are separated by thin layers of conchiolin. The differentiation of natural pearls from tissue-nucleated cultured pearls can be very difficult without the use of this x-ray technique.
Natural and cultured pearls can be distinguished from imitation pearls using a microscope. Another method of testing for imitations is to rub the pearl against the surface of a front tooth. Imitation pearls are completely smooth, but natural and cultured pearls are composed of nacre platelets, which feel slightly gritty.
Different types of Cultured Pearls, including Black Pearls
Black pearls, frequently referred to as Black Tahitian Pearls, are highly valued because of their rarity; the culturing process for them dictates a smaller volume output and can never be mass produced. This is due to bad health and/or non-survival of the process, rejection of the nucleus and their sensitivity to changing climatic and ocean conditions. Before the days of cultured pearls, black pearls were rare and highly valued for the simple reason that white pearl oysters rarely produced naturally black pearls, and black pearl oysters rarely produced any natural pearls at all.
Since the development of pearl culture technology, the black pearl oyster found in Tahiti and many other Pacific Island area has been extensively used for producing cultured pearls. The rarity of the black cultured pearl is now a “comparative” issue. The black cultured pearl is rare when compared to Chinese freshwater cultured pearls, and Japanese and Chinese akoya cultured pearls, and is more valuable than these pearls. However, it is more abundant than the South Sea pearl, which is more valuable than the black cultured pearl. This is simply because the black pearl oyster Pinctada margaritifera is far more abundant than the elusive, rare, and larger south sea pearl oyster – Pinctada maxima, which cannot be found in lagoons, but which must be dived for in a rare number of deep ocean habitats or grown in hatcheries.
Black cultured pearls from the black pearl oyster — Pinctada margaritifera — are not South Sea pearls, although they are often mistakenly described as black South Sea pearls. In the absence of an official definition for the pearl from the black oyster, these pearls are usually referred to as “black Tahitian pearls”.
The correct definition of a South Sea pearl — as described by CIBJO and the GIA — is a pearl produced by the Pinctada maxima pearl oyster. South Sea pearls are the color of their host Pinctada maxima oyster — and can be white, silver, pink, gold, cream, and any combination of these basic colors, including overtones of the various colors of the rainbow displayed in the pearl nacre of the oyster shell itself.
Cultured mabes are grown intentionally, by using a hemispheric nucleus, rather than a round one; and by implanting it against the oyster’s shell, rather than within its tissue. The pearl then develops in a hemispheric form, with a flat back. While in the oyster a mabe pearl is actually considered a blister pearl not a mabe pearl.
Creating Mabe Pearls
After the blister pearl has developed, it is ‘worked’ to become a mabe pearl. Blister pearls are ‘worked’ by cutting the pearl out of the shell with a circle- bit drill. The nucleus is then removed and replaced with a resin. The back of the pearl is then capped with a piece of mother-of-pearl to complete the mabe pearl.
Round pearls are perfectly spherical -- the shape most people think of when they think of a pearl. Because of their relative rarity and "classic" nature, they are highly desirable. Round pearls fall into the spherical category.
The term off-round is used to describe pearls which are 'roundish' to the eye but have a slightly oval or flattened shape. They can still have excellent qualities in terms of lustre or lack of blemish but being off- round makes them less expensive.
Drop pearls are pear- or teardrop-shaped. The drop can either be "long" or "short," depending on its proportions. These pearls make attractive earrings or pendants. This is also a symmetrical shape.
Button pearls are flattened to some degree, making them resemble a button or perhaps a disk rather than a perfect sphere. These pearls are often used in earrings, where the flattened side can be attached to the setting. Buttons are also categorized as symmetrical.
These pearls are shaped like an oval -- narrower at the ends than they are in the center. Ovals are categorized as a symmetrical shape.
Some Pearls for develop with one or more grooves or rings encircling them. These pearls are known as ringed or circled. This adjective can be attached to the primary shape in order to more fully describe the pearl, such as "circled round" or "ringed oval."
This is a pearl which is both non-symmetrical and irregular in shape. The baroque pearl can be purely abstract in its shape, or it can resemble a cross, stick; or some other shape.
These pearls are slightly irregular in their shape. For example, a pearl which might otherwise be considered an oval, button, or drop pearl, but which is not symmetrical in nature, would be considered semi-baroque. Semi-baroque pearls fall into the baroque category of shapes.
The general color of a pearl is also called the body color. Typical pearl colors are white, cream, yellow, pink, silver, or black. A pearl can also have a hint of secondary color, or overtone, which is seen when light reflects off the pearl surface. For example, a pearl strand may appear white, but when examined more closely, a pink overtone may become apparent.
Pearls produce an intense, deep shine called luster. This effect is created when light reflects off the many layers of tiny calcium carbonate crystals that compose the pearl. This substance is called nacre. When selecting a pearl, consider that the larger the pearl, the more nacre it has, so it will also exhibit even more luster. Compare a 5mm Freshwater cultured pearl with a 10mm South Sea cultured pearl and the difference in the amount of nacre is obvious. The difference in luster is as clearly visible as the difference in the pearl sizes.
The size of the pearl greatly depends on the type of pearl. Freshwater pearls range in size from about 3.0–7.0mm, Akoya pearls range from about 6.0–8.5mm, and South Sea and Tahitian pearls can reach sizes as large as 13mm.
One of the main determiners of a pearl’s value is the quality of its surface. Most pearls have some kind of natural blemishes such as pits, bumps, spots of other colors or dullness and tiny surface cracks. The fewer of these imperfections a pearl has on its surface, the more valuable the pearl.
Natural pearls normally have more flaws than cultured Japanese Akoya pearls. That’s because they’ ve been in the oyster longer and have had more time to develop blemishes. Cultured pearls from the South Seas are also more likely to have flaws than Akoyas, which have a thinner nacre coating.
When cared for properly, pearls can last a lifetime. The best way to care for pearls is to wear them often as the body’s natural oils keep pearls lustrous. However, it’s important to keep them away from household chemicals including perfume, makeup and hairspray. Chemicals found in these common products can dull the luster of your pearls. It is recommended that you put your pearls on last when getting ready and make them the first thing you take off when you come home. Before putting your pearls away, wipe them with a soft cloth and store them separate from other jewelry to avoid scratching their tender surfaces.