A pearl is a hard, roundish object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of mollusks, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur.
The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl became a metaphor for something very rare, very fine, very admirable and very valuable.
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 virtually none of these pearls are valued as gemstones.
Nacreous pearls, the most desirable pearls, are produced by two groups of molluscan bivalves or clams. One family lives in the sea: the pearl oysters. The other, very different group of bivalves live in freshwater, and these are the river mussels; for example, see 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. These various species of bivalves are able to make nacreous pearls because they have a thick iridescent inner shell layer called "mother of pearl", which is composed of nacre. The mantle tissue of a living bivalve can create a pearl in the same manner that it creates the pearly inner layer of the shell.
Fine gem-quality saltwater and freshwater pearls can and do sometimes occur completely naturally in the wild state, but this is 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. In modern times however, almost all the pearls for sale were formed with a good deal of expert intervention from human pearl farmers.
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 formed without any human intervention at all, in the wild, and is very rare. A "cultured pearl", on the other hand, is one that has been formed on a pearl farm. The great majority of pearls on the market are cultured 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.
Pearl is considered to be the birthstone for the month of June.
In several European languages, the word 'pearl' is synonymous with 'bead', which can lead to confusion when articles are translated.
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.
Pearls are often white or cream, but the color can vary significantly according to the natural color of the nacre in the various species of mollusk used. Thus pearls can also be black, or various pastel shades.
In addition, pearls (especially freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black.
Freshwater and saltwater pearls may sometimes look quite similar, but they come from very different sources.
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.
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 minerals 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.
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.
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.
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.
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.
Keshi pearls, although they often occur by chance, are not considered natural pearls. They are a byproduct of the culturing process, and hence do not happen without human intervention. These pearls are quite small: typically a few millimeters in size. Keshi pearls are produced by many different types of marine mollusks and freshwater mussels in China. Today many "keshi" pearls are actually intentional, with post-harvest shells returned to the water to regenerate a pearl in the existing pearl sac.
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.
A few species produce pearls that can be of interest as gemstones. These species include the bailer shell Melo (genus), the giant clam Tridacna, various scallop species, Pen shells Pinna (genus), and abalones. Another example is the conch pearl (sometimes referred to simply as the 'pink pearl'), which is found very rarely growing between the mantle and the shell of the queen conch or pink conch, Strombus gigas'', a large sea snail or marine gastropod from the Caribbean Sea. These pearls, which are often pink in color, are a by-product of the conch fishing industry, and the best of them display a shimmering optical effect related to chatoyance known as 'flame structure'.
Somewhat similar gastropod pearls, this time more orange in hue, are (again very rarely) found in the horse conch Pleuroploca gigantea.
The largest pearl known, was found in the Philippines in 1934. It is a naturally-occurring, non-nacreous, calcareous concretion from a giant clam. Because it did not grow in a pearl oyster it is not pearly, instead it has a porcellaneous surface. In other words, it is glossy like a china plate. Other pearls from giant clams are known to exist, but this is a particularly large one.
The pearl weighs 14 lb (6.4 kg) and was supposedly first discovered by an anonymous Filipino Muslim diver off the island of Palawan in 1934. According to the legend as it is currently told, a Palawan chieftain gave the pearl to Wilbur Dowell Cobb in 1936 as a gift for having saved the life of his son. The pearl had been named the "Pearl of Allah" by the Muslim tribal chief, because it resembled a turbaned head. Another even more elaborate legend says that this object is actually the Pearl of Lao-Tzu, a cultured pearl created with a carved amulet and then supposedly progressively grafted into several giant clams, before supposedly being lost due to a shipwreck in 1745. This legend has been discredited, however because this pearl is indeed the product of a giant clam, Tridacna gigas, which cannot be grafted. The pearl is also a whole pearl, not a mabe pearl, and whole pearl culturing technology is only 100 years old.
When Spanish conquistadors arrived in the Western Hemisphere, they discovered that around the islands of Cubagua and Margarita, some 200 km north of the Venezuelan coast, was an extensive pearl bed. One discovered and named pearl, La Peregrina, was offered to the Spanish queen. According to Garcilasso de la Vega, who says that he saw La Peregrina at Seville in 1507, (Garcilasso, "Historie des Incas, Rois du Perou," Amsterdam, 1704, Vol. II, P. 352.) this was found at Panama in 1560 by a negro who was rewarded with his liberty, and his owner with the office of alcalde of Panama.
Margarita pearls are extremely difficult to find today and are known for their unique yellowish color. The most famous Margarita necklace that any one can see today is the one that then Venezuelan President Romulo Betancourt gave to Jacqueline Kennedy when she and her husband, President John F. Kennedy paid an official visit to Venezuela.
Before the beginning of the 20th Century, pearl hunting was the most common way of harvesting pearls. Divers manually pulled oysters from ocean floors and river bottoms and checked them individually for pearls. Not all mussels and oysters produce pearls. In a haul of three tons, only three or four oysters will produce perfect pearls .
The nucleus is generally a polished bead made from freshwater mussel shell. Along with a small piece of mantle tissue from another mollusk to serve as a catalyst for the pearl sac, it is surgically implanted into the gonad (reproductive organ) of a saltwater mollusk. In freshwater perliculture, only the piece of tissue is used in most cases, and is inserted into the fleshy mantle of the host mussel. South Sea and Tahitian pearl oysters, also known as Pinctada maxima and Pinctada margaritifera, which survive the subsequent surgery to remove the finished pearl, are often implanted with a new, larger nucleus as part of the same procedure and then returned to the water for another 2-3 years of growth.
Despite the common misperception, Mikimoto did not discover the process of pearl culture. The accepted process of pearl culture was developed by William Sawville-Kent in Australia and brought to Japan by Tokichi Nishikawa and Tatsuhei Mise. Nishikawa was granted the patent in 1916, and married the daughter of Mikimoto. Mikimoto was able to use Nishikawa's technology. After the patent was granted in 1916, the technology was immediately commercially applied to akoya pearl oysters in Japan in 1916. Mise's brother was the first to produce a commercial crop of pearls in the akoya oyster. Mitsubishi's Baron Iwasaki immediately applied the technology to the south sea pearl oyster in 1917 in the Philippines, and later in Buton, and Palau. Mitsubishi was the first to produce a cultured south sea pearl - although it was not until 1928 that the first small commercial crop of pearls was successfully produced.
The original Japanese cultured pearls, known as akoya pearls, are produced by a species of small pearl oyster, Pinctada fucata martensii, which is no bigger than 6 to 8 cm in size, hence akoya pearls larger than 10 mm in diameter are extremely rare and highly prized. Today, a hybrid mollusk is used in both Japan and China in the production of akoya pearls. It is a cross between the original Japanese species, and the Chinese species Pinctada chemnitzii.
In the past couple of decades, cultured pearls have been produced using larger oysters in the south Pacific and Indian Ocean. The largest pearl oyster is the Pinctada maxima, which is roughly the size of a dinner plate. South Sea pearls are characterized by their large size warm luster. Sizes up to 14 mm in diameter are not uncommon. South Sea pearls are primarily produced in Australia, Indonesia and the Philippines.
Mitsubishi commenced pearl culture with the south sea pearl oyster in 1916, as soon as the technology patent was commercialized. By 1931 this project was showing signs of success, but was upset by the death of Tatsuhei Mise. Although the project was recommenced after Tatsuhei's death, the project was discontinued at the beginning of WWII before significant productions of pearls were achieved.
After WWII, new south sea pearl projects were commenced in the early 1950s in Burma and Kuri Bay and Port Essington in Australia. Japanese companies were involved in all projects using technicians from the original Mitsubishi south sea pre-war projects.
Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China. China has since become the world's largest producer of freshwater pearls, producing more than 1,500 metric tons per year.
Led by pearl pioneer John Latendresse and his wife Chessy, the United States began farming freshwater cultured pearls in the mid 1960's. National Geographic Magazine introduced the American cultured pearl as a commercial product in their August 1985 issue. The Tennessee pearl farm has emerged as a tourist destination in recent years, but commercial production of freshwater pearls has ceased.
The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large, perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants.
Pearls come in eight basic shapes: round, semi-round, button, drop, pear, oval, baroque, and circled. Perfectly round pearls are the rarest and most valuable shape. Semi-rounds are also used in necklaces or in pieces where the shape of the pearl can be disguised to look like it is a perfectly round pearl. Button pearls are like a slightly flattened round pearl and can also make a necklace, but are more often used in single pendants or earrings where the back half of the pearl is covered, making it look like a larger, round pearl.
Drop and pear shaped pearls are sometimes referred to as teardrop pearls and are most often seen in earrings, pendants, or as a center pearl in a necklace. Baroque pearls have a different appeal to them than more standard shapes because they are often highly irregular and make unique and interesting shapes. They are also commonly seen in necklaces. Circled pearls are characterized by concentric ridges, or rings, around the body of the pearl.
In general, cultured pearls are less valuable than natural pearls, and imitation pearls are less valuable than cultured pearls. One way that jewelers can determine whether a pearl is cultivated or natural is to have a gem lab perform an x-ray of the pearl. If the x-ray reveals a nucleus, the pearl is likely a bead-nucleated saltwater pearl. If no nucleus is present, but irregular and small dark inner spots indicating a cavity are visible, combined with concentric rings of organic substance, the pearl is likely a cultured freshwater. Cultured freshwater pearls can often be confused for natural pearls which present as homogeneous pictures which continuously darken toward the surface of the pearl. Natural pearls will often show larger cavities where organic matter has dried out and decomposed.
Some imitation pearls are simply made of mother-of-pearl, coral or conch, while others are made from glass and are coated with a solution containing fish scales called essence d'Orient. Although imitation pearls look the part, they do not have the same weight or smoothness as real pearls, and their luster will also dim greatly.
There is a special vocabulary used to describe the length of pearl necklaces. While most other necklaces are simply referred to by their physical measurement, pearl necklaces are named by how low they hang when worn around the neck. A collar, measuring 10 to 13 inches or 25 to 33 cm in length, sits directly against the throat and does not hang down the neck at all; collars are often made up of multiple strands of pearls. Pearl chokers, measuring 14 to 16 inches or 35 to 41 cm in length, nestle just at the base of the neck. A strand called a princess length, measuring 17 to 19 inches or 43 to 48 cm in length, comes down to or just below the collarbone. A matinee length, measuring 20 to 24 inches or 50 to 60 cm in length, falls just above the breasts. An opera length, measuring 28 to 35 inches or 70 to 90 cm in length, will be long enough to reach the breastbone or sternum of the wearer; and longer still, a pearl rope, measuring more than 45 inches or 115 cm in length, is any length that falls down farther than an opera.
Necklaces can also be classified as uniform, or graduated. In a uniform strand of pearls, all pearls are classified as the same size, but actually fall in a range. A uniform strand of akoya pearls, for example, will measure within 0.5 mm. So a strand will never be 7 mm, but will be 6.5-7 mm. Freshwater pearls, Tahitian pearls, and South Sea pearls all measure to a full millimeter when considered uniform.
A graduated strand of pearls most often has at least 3 mm of differentiation from the ends to the center of the necklace. Popularized in the USA during the 1950s by the GIs bringing strands of cultured akoya pearls home from Japan, a 3.5 momme, 3 mm to 7 mm graduated strand was much more affordable than a uniform strand because most of the pearls were small.
In a Christian New Testament parable, Jesus compared the Kingdom of Heaven to a "pearl of great price" in Matthew 13: 45-46. "Again, the kingdom of heaven is like unto a merchant man, seeking goodly pearls: Who, when he had found one pearl of great price, went and sold all that he had, and bought it."
The language of symbolism was in common use around the time of Jesus Christ; most people were familiar with the symbolic meanings. The circle is a symbol of God because it has no beginning and no end. The circle or pearl was considered to represent Love, Knowledge (the combination of equal amounts of Love and Knowledge is a symbol of Wisdom, the 2 circles intertwined (owl eyes) is symbolic of Wisdom. Some other pearls are Truth, and Faith.
The twelve gates of the New Jerusalem are reportedly each made of a single pearl in Revelation 21:21, that is, the Pearly Gates. "And the twelve gates were twelve pearls; every gate was of one pearl: and the streets of the city were pure gold, as if transparent glass."
Pearls are compared to holy things, in Matthew 7: 6. "Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you."
Pearls are also found in numerous references showing the wickedness and pride of a people, as in Revelations 18: 16. "And saying, Alas, alas, that great city, that was clothed in fine linen, and purple, and scarlet, and decked with gold, and precious stones, and pearls!"
22:23 God will admit those who believe and work righteous deeds, to Gardens beneath which rivers flow: they shall be adorned therein with bracelets of gold and pearls; and their garments there will be of silk.
35:33 Gardens of Eternity will they enter: therein will they be adorned with bracelets of gold and pearls; and their garments there will be of silk.
The Quran describes the wives of the people of Paradise as having eyes that are similar to pearls:
56:22-23 And [there will be] Houris with wide lovely eyes [as wives for the pious], Like unto preserved pearls.
The handsome young boys in paradise are similarly depicted:
52:24 Round about them will serve, [devoted] to them, youths [handsome] as pearls well-guarded.
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Calcitic nacreous ultrastructures in Bryozoans: implications for comparative biomineralization of lophophorates and Molluscs.
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