Physical properties

The unique luster of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers become thinner and more numerous. The iridescence that some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, purple, or black.

Freshwater and Saltwater Pearls

Pearls fit into two categories: freshwater and saltwater. As their name implies, freshwater pearls are formed in freshwater mussels that live in lakes, rivers, ponds and other bodies of fresh water. Most freshwater cultured pearls sold today come from China. By contrast, saltwater pearls grow in oysters that live in the ocean, usually in protected lagoons. Akoya, South Sea and Tahitian are the three main types of saltwater pearls.

Natural and Cultured Pearls

Creation of a Pearl

The difference between natural and cultured pearls focuses on whether the pearl was created by nature, without man's intervention, or with the help of man. Pearls are formed inside the shell of certain bivalve mollusks. As a response to an irritant inside its shell, the mollusk will deposit layers of calcium carbonate (CaCO₃) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin.  This combination of calcium carbonate and conchiolin is called nacre, or as most know it, 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

Natural pearls are 100% nacre. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or grain of sand enters an oyster (or other mollusk) and settles inside the shell. It takes about 8 months to create one. The oyster, being irritated by the intruder, secretes the pearl substance called nacre to cover the irritant. This process is repeated for many years, thus producing a pearl.

Different types of Cultured Pearls

Cultured Pearls

'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 will reveal a different structure to that of a natural pearl. It exhibits a solid center with no concentric growth rings, compared to a solid center with growth rings. A natural pearl however is solid nacre or 100% pearl. Also it is an all-natural shape, round being the most rare formation.

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 (the small object such as a tiny fish, grain of sand or crab that slips naturally inside an oyster's shell or inserted by a human), 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 natural black pearls, and black pearl oysters rarely produced any natural pearls at all. Since 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 due to the fact that 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. 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 body itself.

Largest Pearl

The largest pearl ever found so far, came from the Philippines in 1934.  It weighed 14 lb (6.4 kg) when it was discovered by an anonymous Filipino Muslim diver off the island of Palawan.  Later, 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.  It is believed to actually be the Pearl of Lao-Tzu which was lost due to a shipwreck in 1745.

Jewelry

Pearls come in eight basic shapes: round, semi-round, button, drop, pear, oval, baroque, and ringed. Perfectly round pearls are the rarest and most expensive, and are generally used in necklaces, or strings of pearls. 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. Ringed pearls are characterized by concentric ridges, or rings, around the body of the pearl.

In general, cultivated pearls are less valuable than natural pearls, and imitation pearls are the least expensive. One way that jewelers can determine whether a pearl is cultivated or natural is by x-raying the pearl. If the grit in the centre of the pearl is a perfect sphere, then the jeweler knows it is cultivated. This is because when the cultivators insert the grit, (usually a polished piece of mussel shell), it is always perfectly round, so as to produce a more expensive, perfectly round pearl. If the centre is not perfectly round, the jeweler recognizes that it is genuine, and gives it a higher value. Imitation pearls are much easier to identify by jewelers. 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 also a unique way of naming pearl necklaces. While most other necklaces are simply referred to by their physical measurement, strings of pearls have their own set of names that characterize the pearls based on where they hang when worn around the neck. A collar will sit directly against the throat and not hang down the neck at all; they are often made up of multiple strands of pearls. Pearl chokers nestle just at the base of the neck. The size called a princess comes down to or just below the collarbone. A matinee of pearls falls just above the breasts. An opera will be long enough to reach the breastbone or sternum of the wearer, and longer still, a pearl rope is any length that falls down farther than an opera.

Necklaces can also be classified as uniform, where all the pearls are the same size, graduated, where the pearls are arranged in size from large in the centre to smaller at the ends, or tin cup, where pearls are generally the same size, but separated by lengths of chain.

Gemological Identification

A well equipped gem testing laboratory is able to separate natural pearls from their cultured pearls, non-nucleated cultured pearls and imitation 'pearls' counterparts. The separation between a natural pearl or cultured pearl is almost impossible without a bona-fide gemological X-ray certificate.  However, density can be an indicator. Cultured pearls are often lighter in weight owing to their inner 'bead'.

Value of a Natural Pearl

Quality natural pearls are very rare jewels. Actual value of a natural pearl is the same as other "precious" gems, and depends on size, shape and quality. Natural Pearls have become even rarer since most mollusks are used to create cultured pearls, and thus the chance of finding a natural pearl (or the patience to go look for them) is further reduced. Most natural pearls are therefore sold to individual collectors as a collector's item, and rarely used in jewelry such as necklaces. One example of rare natural pearls are bright orange Melo Pearls. Another example are the original Keshi pearls, which actually occur in the mantle of a mollusk where it is formed as a byproduct of the "main pearl". These pearls were quite small: typically a few mm in size. Nowadays Keshi pearls are used for many different types of cultured South Sea pearls and even for the cheaper Chinese Sweetwater pearls.

History

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 natural oysters produce pearls. In a haul of three tons, only three or four oysters will produce perfect pearls. However, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. The pearls are usually harvested after one year for Akoya, and 2-4 years for Tahitian and South Sea. This mariculture process was first developed by Tatsuhei Mise Tokishi Nishikawa in Japan. The nucleus is generally a polished bead made from 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 the oyster. South Sea and Tahitian pearl oysters, also known as Pinctada margaritifera and Pinctada maxima, 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 patent the process of pearl culture. The accepted process of pearl culture was developed by a team of scientists at Tokyo University between 1907 and 1916. The team was headed by Nishikawa and Tatsuhei Mise. Nishikawa was granted the patent in 1916, and married the daughter of Mikimoto. Mikimoto was able to use the technology after the patent expired in 1935. After the patent was granted in 1916, the technology was immediately commercially applied to Akoya pearl oysters in Japan in 1916. Tatsuhei's brother was the first to produce a commercial crop of pearls in the Akoya oyster. Mitsubishi 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 1931 that the first small commercial crop of pearls was successfully produced. Pearl culture technology was not applied commercially to the Tahitian black pearl oyster until the 1970s.

The original Japanese cultured pearls, known as Akoya pearls, are produced by a species of small oysters, Pinctada fucata, no bigger than 6 to 7 cm in size, hence Japanese pearls larger than 10 mm in diameter are extremely rare and highly prized. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean. One of the largest pearl-bearing oysters is the Pinctada maxima, which is roughly the size of a dinner plate. South Sea pearls are characterized by their large size and silvery color. Sizes up to 14 mm in diameter are not uncommon. Australia is one of the most important sources of South Sea pearls. Tahitian pearls (also referred to as Tahitian pearls) are also another South Sea pearl. 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. 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. Despite often being described as black south sea pearls, Tahitian pearls are not south sea pearls. The correct definition of a south sea pearl is "the pearl produced by the pinctada maxima pearl oyster."

In 1914, pearl farmers began culturing freshwater pearls using the pearl mussels native to Lake Biwa. This lake, the largest and most ancient in Japan, lies near the city of Kyoto. The extensive and successful use of the Biwa Pearl Mussel is reflected in the name Biwa pearls, a phrase which was at one time nearly synonymous with freshwater pearls in general. Since the time of peak production in 1971, when Biwa pearl farmers produced six tons of cultured pearls, pollution and overharvesting have caused the virtual extinction of this animal. Japanese pearl farmers now culture a hybrid pearl mussel — a cross between the last remaining Biwa Pearl Mussels and a closely related species from China — in other Japanese lakes such as lake Kasumi Ga Ura.

In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. Freshwater pearls are characterized by the reflection of rainbow colors in the luster. Cultured pearls are also produced using abalone.

Religious References

According to Rebbenu Bachya, the word Yahalom in the verse Exodus 28:18 means "Pearl" and was the stone on the Hoshen representing the tribe of Zebulun. This is extremely disputed among scholars, particularly since the word in question in most manuscripts is actually Yasepheh - the word from which jasper derives; scholars think that refers to green jasper (the rarest and most prized form in early times) rather than red jasper (the most common form). Yahalom is usually translated by the Septuagint as an Onyx, but sometimes as a beryl or as a jasper; Onyx only started being mined after the Septuagint was written, so the Septuagint's term Onyx probably doesn't mean Onyx - Onyx is originally an Assyrian word meaning ring, and so could refer to anything used for making rings. Yahalom is similar to a Hebrew word meaning hit hard, so some people think that it means diamond. The variation in possibilities of meaning for this sixth stone in the Hoshen is reflected in different translations of the Bible — the King James Version translates the sixth stone as diamond, the New International Version translates it as emerald, and the Vulgate translates it as jaspis — meaning jasper. There is a wide range of views among traditional sources about which tribe the stone refers to.

In a Christian New Testament parable, Jesus compared the Kingdom of Heaven to a Pearl of Great Price.  Additionally, the twelve gates of the New Jerusalem are reportedly each made of a single pearl Revelation 21:21, that is, the Pearly Gates. The metaphor of a pearl appears in the longer Hymn of the Pearl, a poem respected for its high literary quality, and use of layered theological metaphor, found within one of the texts of Gnosticism.

Islamic References

In Islam, the Koran often mentions that dwellers of paradise will be adorned with 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.

Also, 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.

Asian Astrological Belief in Natural Pearls

The Vedic tradition describes the sacred Nine Pearls which were first documented in the Garuda Purana, one of the books of Hindu holy text Atharvaveda. According to Marco Polo the kings of Maabar (now known as the Coromandel Coast wore a necklace of 104 rubies and 104 precious pearls which was given from one generation of kings to the next. The reason was that every King had to say 104 prayers to his "idols" every morning and every evening.  At least until the beginning of the 20th century it was a Hindu custom to present a completely new, undrilled pearl and pierce it during the ceremony.

Information courtesy of Wikipedia.org