General

Pearls are hard (Mohs scale 2.5 - 4.5; usually 3.5 - 4), round objects which are produced mostly in the shell of a living mussel to seal off an irritant inside the shell. Pearls can be produced by any mussel, in fresh water or salt water. Freshwater pearls are produced by freshwater mussels (Unionidae and Margaritiferidae), which live in lakes, rivers etc. Marine pearls are usually produced by pearl oysters (Pteriidae) that live in tropical oceans but also by a sea snail (Strombus Gigas) in the Caribbean.
Most natural pearls are not attractive, and not very durable. Fine quality pearls are highly valued, and usually accepted as gemstones since ancient times. They have also been crushed for use in cosmetics or in paint formulations. Desirable pearls can be produced by nature or with human intervention (cultured pearls).
Typical natural stimuli are caused by small intruders or parasites which enter a bivalve mollusk when its shell valves are open for feeding or respiration. The mussel, irritated by the intruder, tries to cover the irritant with secretes of nacre. This is repeated many times, thus producing a pearl. Natural pearls consist of nearly 100% nacre. In cultured pearls, the irritant is typically a cut piece of the mantle.
A mollusk's mantle deposits layers of calcium carbonate (CaCO₃), mineralized as aragonite or calcite. The layers are hold together by an organic compound called conchiolin (sometimes referred to as conchin). This combination of CaCO₃ and conchiolin is called nacre or "mother-of-pearl".

History

Thousands of years ago human beings have discovered the first pearl, probably while searching a beach for food. Because of the beauty of pearls, and their rarity, they have become one of the most sought-after gem. Pharaos were buried with them, Greeks associated pearls with love and marriage, Romans considered them as symbol of wealth and social standing. In the Middle Ages one believed that pearls can protect from harm. In the 17th century greed for sea-grown pearls resulted in the depletion of nearly all pearl oysters in America. Until the early 19th century, pearls were accessible only to rich and famous people. Only the modern pearl cultivation made pearls available also to common people.
Chinese had cultured semi-circular pearls since the 14th century. Later American, French, and Swedish scientists tried to get pearls from mussels. In 1907 two Japanese (Tatsuhei Mise and Tokichi Nishikawa) discovered how to get pearls by cultivation. Today cultivated pearls are closely related to the Japanese Kokichi Mikimoto (1858 - 1950) who started experimenting with the culture of pearls in 1888. In 1896 he obtained a patent for producing half pearls, in 1908 he applied for a patent to produce full pearls. In the 1920's, when Japanese cultured pearls were introduced into the jewelry market, pearl buyers were confused and viewed them as "fake natural" material, but within a few years Japanese cultured pearls were accepted as real as natural ones, simply being encouraged by human ingenuity.

Cultivating Pearls

About two thousand independent pearl growers harvest pearls in Japanese waters, using the same basic techniques to grow perfect cultured pearls. Highly skilled technicians carefully open living pearl oysters, and make an incision in the mussel's body, called "nucleation", "grafting" or "seeding". Then a small piece of mantle tissue from another oyster is placed into the mussle. Then a small, round piece of nacre bead (any form available) is placed beside the inserted mantle. The mussel is then returned to sheltered, rich in nutrients bays. The mussel grows, and deposits more and more layers of lustrous nacre around the implanted nucleus, following the shape of the implant. A daily check of all necessary conditions (water temperature, feeding conditions etc.) is necessary to get the best results. From time to time the mussels are lifted from the water to clean them from seaweed and other strange organisms, to treat them with chemical compounds against parasites, and to see how they "feel". After 2 - 3 years the pearls can be harvested. The surviving mussels are brought ashore and opened to get their valuable content.
Every year millions of mussels are nucleated but only a few mussels survive, and about 50% of them finally produce quality pearls. Therefore even cultivated pearls are rare and valuable. Less than 5% of all mussels yield gemmy pearls of perfect shape, lustre and color. After harvesting, all pearls must be sorted, which is a very difficult and time-consuming work. Each pearl has to be sorted by size, shape, color and lustre. Then the pearls are drilled. Finally experts must compare pearls that are similar in size, shape, lustre and color so that they fit together for a necklace or a pair of earrings.

Quality Factors

1. Lustre
Lustre is the most important quality factor in pearls. Lustre refers to a pearl's brilliance (light reflection). The lustre is evaluated from low (low reflections, too white, dull, chalky, because of a small nacre thickness) to high (clear reflections, bright, deep-seated glow because of a thick nacre).
2. Surface
The cleaner the surface of a pearl, the more valuable it is. Surface quality depends on the amount and kinds of flaws that appear on the pearl. It ranges from blemished (dominated by spots, bumps, pits, cracks, circles or wrinkles) to clean (no flaws). Natural imperfections don't necessarily detract from the beauty or value of a pearl.
3. Shape
Pearls are subdivided into several categories: "round", "drop" (ovoid or tear drop-shaped), "button" (dome-shaped), "oval", "semi-round", "circle / ringed", "baroque" (irregular spheroidal), "semi-baroque", "dog-tooth" (roughly tusk-like), "egg", "pear" ("pear drop" or "pear eye"), "turtle-back" (irregular surface pattern like a turtle's shell) and "wing" (resembling a wing or a part of it). Absolutely round pearls, of course very rare, are most valuable.
4. Color
Saltwater pearls nearly show the entire spectrum of colors. No color is dominating the other because a "favourite color" depends on the customer's taste.
Colors: white or off-white (commonly bluish or yellowish), reddish, pink, yellowish, golden, orange, greenish, blueish, lavender, brownish, bronze, blackish and gray. White pearls usually show light hues of one or more other colors (as "overtones"). "Orient pearls" show a subtle play of overtones, then called e.g. "rosé orient".
5. Size
Pearl's sizes are measured in mm (millimeters / 1 mm = 0.039 inches), through the diameter of a pearl. The size is no indicator of a pearl's quality or value but larger pearls are usually worthier than smaller ones, depending on equal size, color and lustre. Young pearls can be smaller than 1 mm, old ones bigger than 2 cm. Most available pearls are 7 mm (0.27 inches) in diameter.

Types

1. "Akoya Pearls"
Bead-nucleated pearls, implanted with spherical beads carved out of natural shell. Probably the most popular cultured pearls which grow in Japan and China (species: "Pinctada martensii" and "Pinctada fucataoyster"), although only the third most valuable commercially produced pearl. The cold water temperature allows the mussels to produce uniform pearls with a brilliant luster within approximately one year. The average size of a pearl is 6 - 7 mm. Colors: rose, silver, white, cream, gold, grey-blue. Akoya mussels are more difficult to farm than freshwater mollusks because of a higher mortality rate and natural disasters like typhoons. Akoya pearls are rounder than traditional freshwater pearls and higher valued than the Chinese freshwater pearl. The Akoya oyster is the smallest farmed oyster. Therefore its pearls are usually small. The typical Akoya pearl measures only 7 mm. Akoya pearls are usually round, although a certain percentage of baroque and keshi pearls is produced.
Japan has been the Akoya pearl producing center of the world until China started to produce pearls of equivalent quality in a greater abundance. Meanwhile Japan imports smaller Akoya pearls from China.

2. "South Sea Pearls"
The most valuable cultured pearls today, grown in the warm waters of Australia, Indonesia, the Philippines, Myanmar and Thailand. Available in white, silver, pink, gold, cream and any combination of these colors. These pearls are produced by two varieties ("Silver Lipped Oyster" and "Gold Lipped Oyster") of the oyster "Pinctada maxima". Native people dived / dive (10 - 80 m deep) for these pearls throughout the warm Pacific Ocean. Since the 16th and 17th century South Sea pearls developed a global demand. Since the 20th century, over 400 boats with approximately 3,500 divers operated in Australia alone. In the mid 1990’s, South Sea pearls became available in large quantities so that people could purchase pearls worldwide, for an acceptable price. It takes between 20 to 24 months to grow a South Sea pearl, not regarding all the complications that can cause them to die. Natural oysters are mixed with the hatchery stock to keep the population healthy.
South Sea pearls are available between 9 to 20 mm, and can be white, silver, pink, and gold. 10 - 30% of each harvest produces round or near-round pearls. South Sea pearls are generally larger than other pearls and have a higher value than other pearls.

3. "Tahitian Pearls"
Tahitian pearls are considered to be the second most valuable farmed pearls worldwide. Tahitian pearls grow in the "Pinctada margaritifera cumingi" oyster (the "Black Lipped Oyster"), not directly cultivated in Tahiti, but mainly throughout the islands and atolls in the middle of the South Pacific Ocean, called French Polynesia (since 1880). Only 1 of 10,000 oysters produces a pearl, within 22 - 26 months. Therefore there cannot be a mass production. The pearl's size usually ranges from 8 – 18 mm. The largest Tahitian pearl was 25 mm. Until today there is an increasing market on Tahitian pearls. Tahitian pearl oysters (especially from the Gambier and Tuamotu islands) quickly became depleted, nearly to extinction. Fortunately, after strict regulations by the government, oyster beds could be to repopulated. Therefore, in the mid 1960ies, Tahitian cultured pearls could be harvested again. Today French Polynesia supplies the world with the most perfect cultivated pearls. They are also farmed in the Cook Islands, the Micronesian Islands, Japan, Thailand and the Philippines.
Black Tahitian Pearls are highly valued because of their rarity. The black cultured pearl is still rare in comparison to Chinese freshwater cultured pearls and Japanese cultured pearls. Tahitian pearls typically have a naturally dark body colour, showing the colors black, creamy white, and blackish grey, silver, rose, blue, green, and aubergine / purple.
Matching these pearls into a fine necklace is a great task which requires the comparison of thousands of loose pearls.

4. "Keshi Pearls"
Keshi pearls, a bi-product of pearl farming, are highly lustered but small. They are created by saltwater or freshwater mussels which "rejected" an implanted nucleus. They don't have a nucleus and consist of 100% nacre. Therefore most Keshi pearls have a better luster than the best-quality cultured pearls.
Keshi pearls are rare pieces. Today the pearl farmers X-ray their oysters to search for nuclei that have been expelled. When they find such a nucleus-free mussel they re-nucleate it. Therefore Keshi pearls tend to be rare.

5. "Oriental Pearls"
No cultured but natural pearls from the Persian Gulf. Some pearls from Africa are also named "Oriental pearls" because they cannot be easily distinguished from the Persian Gulf pearls.

6. "Occidental Pearls"
Pearls from the Atlantic or Pacific Coast of Central America. Larger, but less well shaped and duller than "Oriental pearls".

7. "Conch Pearls"
One of the rarest pearls (although containing no nacre) worldwide, created by the "Strombus Gigas" sea snail. Every year 2,000 - 3,000 of these pearls are fished around the coasts of the Bahamas, Florida, Yucatan and the Antilles. Only a few of them can be used for jewelry.

8. "Melo Melo Pearls"

Melo Melo Sea Snail *

Very rare pearls, produced by the rare "Melo Melo marine snail" (or zebra sea snail) which lives in the South China Sea and the Bay of Bengal. Like conch pearls, it contains no nacre. These pearls are very large and very round. The colors range from yellowish to dark brown although orange is the most desirable color.

* Photo by kind permission of © www.palagems.com, Bill Larson.



9. "Abalone Pearls"
These pearls come from the Abalone sea snail family, found throughout all oceans. The New Zealand Abalone species ("Haliotis iris", called "Paua") produces the greatest range of colors and iridescence of any abalone shells. It lives in the cool waters of the New Zealand coast.

10. "Freshwater Pearls"
Fresh water pearls are mantle-tissue nucleated. These pearls are formed by mussels in lakes, rivers, ponds, and other freshwater bodies, especially in China and Japan. China is increasing the pearl cultivation, improving processing techniques and expanding the sales. "Beadless", "seedless" or "non-nucleated" cultured pearls which grow around a tissue graft (e.g. a piece of mantle). A large number of them are cultured in former rice fields in China, one of the first private enterprises once allowed by the Chinese government.
A mussel can produce up to 40 pearls. Today freshwater mussel farming can produce large quantities. Within 3 - 7 years a mussel can produce pearls between 3 – 13 mm, with a 40% chance of getting round pearls. Freshwater pearl colors: white, pink, peach, lavender, grey, yellow and cream. "American pearls" is a widely applied name for freshwater pearls from North America. Most freshwater pearls from Europe are from the mussel "Margaritifera margaritifera". It can be found in Spain, France, Belgium, Luxemburg, Germany, Austria, Czech Republic, Ireland, Great Britain, Scandinavia and Russia.

11. "Blister Pearls"
Blister pearls are natural or cultured, flattened, irregular pearls with attached pearly concretions. They are formed between the tissue and the mantle of a mussle. They can contain clay, water and other things. Blister pearls, especially grown in abalone mussels, can show a striking iridescence. Blister pearls from Paua mussels are very colorful.

12. "Scallop Pearls"
New, rare type (since 2000) of natural pearls which is harvested at the coast of Baja California (USA) from the "Mano de Leon" scallop "Nodipecten subnodosus". These pearls show a mosaic-like pattern that covers the surface of and shows a metallic effect. Colors: salmon or mauve from white to deep royal purple with varying shades of oranges, pinks and plums. These pearls mostly appear in symmetrical forms but can also be found in baroque forms like "buttons", "rounds", "drops", and "ovals".

Identification of natural Pearls

In ancient Rome one silver-plated glass spherules and coated them with a glass film in order to create lustrous pearls. Ancient Indians created baked pearls from clay spherules, coated with mica powder. Since the late 20th century, pearl imitations were produced by coating mother-of-pearl, glass or carbonate spherules. Lead carbonate, bismuth and mica powder became usual for creating imitations. These substances give the surface of an imitated pearl a luminous, white appearance. Also plastic was / is used to create "bijoux jewelry". Glass beads were / are coated with a certain "essence d'orient", a substance made from fish scales. This gives the imitations a luster that nearly resembles natural or cultured pearls.

1. X-rays Test
Cultured pearls and imitated pearls can be sufficiently distinguished from natural ones only by X-ray examination. If X-rayed and photographed, a cultured pearl shows a solid center without concentric growth rings, in contrary to a natural pearl.
Imitated pearls are opaque, and look black or white on an X-ray photo [depending on the positive (black) or negative (white) print]. Natural pearls are semitransparent to x-rays, resulting in a grayish X-ray picture.

2. Refractometer Test
A refractometer is an instrument that measures the degree to which light is bent as it passes through a gemstone. Natural and cultured pearls generally have a reading between 1.530 and 1.685. The numerical difference ("birefringence") between these readings is .155 which is much higher than the birefringence of other gems. This causes a blinking, pink effect when seen through a rotating Polaroid filter; and it is a proof that a pearl is no imitation.

3. Tooth Test
Cultured or natural pearls feel gritty or sandy when rubbing them along the biting edge of the upper front teeth. Imitations usually feel smooth. This test is not sufficient because sometimes cultured pearls can feel also smooth, and imitations can feel gritty.

4. Magnification Test with a 10x Loupe
After having examined many artificial and natural pearls and their typical surfaces, one doesn't need other methods than loupe examination any more. Nevertheless here are some test criteria: Clean, natural pearls have a very fine-grained surface in contrary to most imitations which look more grainy. Unfortunately freshwater pearls and South Sea pearls have a more grainy surface than other natural pearls so that it needs much experience to distinguish them from imitations if other methods are not additionally used. Imitations usually don't show any flaws under a loupe. Natural flaws are different from possible flaws on the surface of imitations.

5. Matching Necklace Pearls / Overtones
If shape, luster, size and color (resp. overtones) of the pearls of a necklace match perfectly, it probably consists of imitations. Natural and cultured pearls usually slightly differ re shape, color overtones etc. Necklaces sometimes include natural or cultured pearls combined with imitations. That complicates the identification of faked necklaces.

6. Weight
Cultured and natural pearls (specific gravity: 2.61 - 2.85 / heavier than 2.75 is a widely used criterion to distinguish pearls as cultured rather than natural) are heavier than plastic or wax-filled ones but more or less similar to glass imitations ((spec. grav. of ordinary glass is 2.5 g/cm³).
Wax-filled imitations (e.g. "Bourguignon pearls" or "Venetian pearls") are made of a hollow glass sphere, coated with "Pearlessence" / "Essence d’Orient" and then filled with wax. "Essence d’Orient" is the invention of a Parisian rosary maker who realized that fish scales give off a pearly substance which floats on the water. He mixed this iridescence substance with varnish and created the "Essence d’Orient" which he probably used to coat the insides of glass beads, and finally filled them with wax.

7. Drill Hole Test
One can examine the drill holes of necklaces pearls with a 10x lupe. Cultured pearls usually show these characteristics: A clear dividing line between the nacre and nucleus. Sharp edges of the drill hole which looks like a straight cylinder. The nacre coating is thicker than the coating of imitations.
Imitations usually don't have a dark dividing line between the coating and the rest of the pearl. The coating around the edges of the drill holes may be uneven. The thinness of the coat can be seen at the edge of the drill hole.
The bead's glassy luster is apparent.

8. Additional Informations
Mother of pearl spherules can be covered with an iridescent nylon film, created by repeated immersion into plastic substances, mixed with lead carbonate, mica and titanium oxide. After several drying processes after each immersion, these "bathed pearls" are finally polished and offered as "improved cultured pearls". The more immersions the better the result.
"Majorcan Pearls" are considered to be the finest simulated pearls. Each of about 30 layers is created by dipping the core (probably particially made of plastic or porcelain) into a bath of cellulose acetate and cellulose nitrate, then allowing it to dry, then polishing it. The specific process remains a secret to the producers.
Valuable necklaces are made of precious metals. If its clasp is made of silver, steel or a gold plated metal, be warned! On the other hand valuable pearls are sometimes combined with cheap clasps, and the other way round.
If a pearl's or a necklace's price is extremely low, it can be an imitation. Valuable pearls are never sold below their cost.

⇐ Intro Page ⇐ Gemstones ⇐ Pearls