The Different Kinds of Cultured Pearls

Pearls are organic gem materials form in a variety of mollusks when the mollusk covers an irritant with layers of nacre. Oysters, mussels, conch, and abalone can produce pearls. Oysters and mussels can do this job by themselves when an irritant accidentally enters its shell to produce natural pearls or can be aided by man introducing a bead into the mollusk to produce cultured pearls.

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By Sondra FrancisMore from this author

Pearls are organic gem materials form in a variety of mollusks when the mollusk covers an irritant with layers of nacre. Oysters, mussels, conch, and abalone can produce pearls. Oysters and mussels can do this job by themselves when an irritant accidentally enters its shell to produce natural pearls or can be aided by man introducing a bead into the mollusk to produce cultured pearls.

Colors:White, cream, gray, black, pink, orange and violet tints, pink and green overtones plus dyed colors
R.I.:1.53 - 1.69
S.G.:2.68 - 2.85
Treatment:Bleaching, dyeing and irradiation
Hardness:2 1/2 - 4 1/2
Availability:Natural pearls: very rare; cultured pearls: supply meets demand
Localities:Japan, Persian Gulf, China, Australia, Tahiti and USA
Price:Low to very expensive
Common shapes:Round, baroque, button shaped, drop shape and more
Pearl in oyster photo by Pearl Sales Institute
Pearl in oyster photo by Pearl Sales Institute

Natural Pearls

Natural pearls are created by mollusks to protect themselves from natural irritants such as grains of sand, minute parasites, or other small foreign bodies. As a defense mechanism, the mollusk forms layers of nacre over the irritant; nacre gives the pearls their lustrous appearance. Pearls found in the Persian Gulf are called Oriental pearls. Oriental pearls are among the most treasured gems in history. Natural saltwater pearls have also been found off the coast of Venezuela, Tahiti, Gulf of Manaar, Australia, and other warm water areas. Today natural pearl supplies have virtually ceased due to a lack of divers, oyster shortages and pollution. Occasionally new pearls are found but no steady supply exists. Natural pearls can be found in antique jewelry and sometimes are available at auctions.

Other exotic and rare pearls are formed in abalone and conch shells. If you would like to look at these pearls, you may have to search a while to find a few. Conch pearls are generally a pink color that resembles the inside of the conch shell. The abalone pearl looks a bit like the abalone shell with iridescent blue and green colors. These pearls are rare and fine specimens fetch prices in the expensive range.

Freshwater pearls form in mussels in various rivers of the world. Freshwater pearls were very popular in Art Nouveau jewelry and the river sources of Scotland and Wales were depleted in the search of these rare white free form pearls.

Cultured Pearls

In 1910 a process was patented in Japan to create pearls with the help of the human hand. Kokichi Mikimoto led the Japanese cultured pearl growers in the development of this industry. The process involves the surgical implantation of a round shell bead into the meat of an Akoya oyster. These impregnated oysters are put into baskets and put back into the sea for a period of time that ranges from less than a year up to three years. The longer the oyster is in the water the more nacre forms around the implanted bead and the greater the likelihood of creating a fine pearl. This may seem simple enough, but each year the oyster is left in the water about 25% of the oysters die. Consequently, fine quality cultured pearls are expensive to grow.

South Sea Cultured Pearls

South Sea cultured pearls are cultured in warm water areas in a manner similar to the Japanese culturing. Different oysters are used and these can produce larger white to silvery pearls, black pearls and gold pearls and occasionally some rare pink and other exotic colors. South Sea pearls are defined as those that are grown in tropical seas; they are grown in Tahiti, Australia, Myanmar (Burma), Indonesia, the Philippines, and Thailand. Generally South Sea pearls are larger in size than Japanese cultured pearls; Japan rarely produces pearls that are l0 millimeters or more in diameter. South Seas pearls generally range in size from 8 to 20mm. Larger ones have been seen, but rarely. Strands of fine South Sea cultured pearls are very expensive. Even high quality single South Sea cultured pearls are expensive. Natural pearls are also found in the South Sea areas but again these are extraordinarily rare and found by chance.

Photo by Pearl Sales Institute

Freshwater Cultured Pearls

Freshwater cultured pearls are grown in Lake Biwa in Japan, in the People's Republic of China, and in some tributaries of the Mississippi River in the United States. Freshwater pearls are grown in mussels and are cultured in a variety of shapes and exotic colors. Strands of small freshwater "rice" pearls can be very inexpensive and have been produced in abundance in China.

In freshwater pearl culturing the mantle tissue of the mollusk is planted in the lip of the mussel; many pearls can be produced at one time and the mussels do not have to be killed to remove the treasures! Freshwater cultured pearls are grown in lustrous white, soft to medium pinks, pastel oranges and pinkish mauve colors; sometimes golden iridescence is found in these fancy colors. Freshwater pearls are usually small in size, fairly baroque in shape and these fall into a very affordable price range. Today large, round fresh water cultured pearls are grown in China. They can range from 8 to 13mm in diameter. As with saltwater pearls, as freshwater pearls become larger in size, the price goes up.

Keishi Pearls

Keishi pearls are accidents of the pearl's culturing process. They form from oyster mantle that is attached to the mother-of-pearl bead that is inserted into the oyster. Keishi, always irregular in shape, occur in Japanese and South Seas culturing processes. Usually they are silvery, white or black in color; occasionally a fancy colored one is born.

Other pearl-like products

The shell portion of a mollusk can produce some exotic gem materials. Blister pearls develop in the shell and have a "pearly" luster and free form shape. Mabe pearls are artificially induced "blister pearls" created by putting a preshaped piece of mother of pearl against the shell of the mollusk. Mabe pearls can be formed in a variety of shapes: rounds, drops, hearts and many other shapes are possible. Mabe pearls are generally white. Finer qualities may have pink overtones. Mabe pearls can be formed into nearly spherical shapes; these are much less expensive than cultured pearls of similar size and luster.

Quality factors in pearl grading

The grading factors for valuing pearls are complex, but the same factors are used for grading whether the pearls are natural or cultured, salt water or fresh water. The prices of natural pearls may be ten or more times the prices of an equal quality of cultured pearls. The rarity of natural pearls is the obvious reason. If natural pearls are outstanding in size, shape, color, luster, or matching in quality, the price may be beyond any multiple of cultured pearl prices.


Generally strands of cultured pearls are evaluated by millimeter size of their diameter. Uniform pearls are sold according to a half millimeter range in a strand. Strands will be sold as 7 to 6 1/2 millimeters, 5 to 5 1/2 millimeters and so forth. Graduated cultured pearls will vary diameters in strands although common strand size ranges from 3 to 7 mm. The size of the pearl affects value dramatically. The larger the size, the more expensive the pearls or the strand. However, small cultured pearls, between two to four millimeter, can cost as much to produce as five millimeter pearls so strands of smaller pearls may be disproportionally expensive. When cultured pearls exceed eight millimeters they jump drastically in price. For sizes over ten millimeters in the finest qualities, a single pearl will fall in the expensive category. For loose pearls, natural pearls are weighed in grains and cultured pearls are weighed in mommes. A grain is the equivalent of one-quarter of a carat (four grains to a carat) and a momme equals l8.75 carats (or 3.75 grams or 75 pearl grains).


Many shapes are possible for pearls; shape is extremely important for determining value. Round spherical pearls are the most expensive and prices drop as the shape departs from round. Strands of salt-water cultured pearls are graded into round, semi-rounds, semi-baroques, and baroques. If you would like a strand of fine pearls but want you to save money, choosing a strand of semi-rounds or semi-baroques can give you beauty and substantial savings.

Other pearl shapes include button shapes, drop or pear shapes, and any uniquely shaped piece falling into a baroque classification. Usually these departures from round will drop in price with some exceptions; matched pairs of pearls in an interesting shape may sell for premiums and very unusual shapes may command higher prices especially if some promoter names it or features it as an "art work".

Freshwater pearls are also valued according to shape with those closest to round fetching the highest prices unless the pearls falls into the "art" category.


Color is always a critical factor in determining the price of any gem material. In Japanese cultured pearls they will come in white, shades of cream, white or cream with pink overtones, white or cream with green overtones, and shades of yellow. South Sea cultured pearls come in white, silvery white, cream, yellow to gold, pink, black, shades of silver gray and these may have overtones in pink, blue, green, and bronze. Freshwater cultured pearls are grown in white, pink, orange, and violet pastels with bronze, gold, other exotic overtones.

In Japanese cultured pearls the white or very light cream pearls with rose overtones command the highest price with prices dropping as the pearls approach a visible yellow color.

Photo by Pearl Sales Institute

In South Seas cultured pearls, well, this can get complicated. Rare or exotic colors will be highly priced if all other factors fall into the fine category. Fine black South Seas cultured pearls are generally the most expensive with fine whites following. There will be a lot of other factors in determining the value of South Seas pearls so just looking at color is limiting.(Black Tahitian pearl. Photo by Pearl Sales Institute)

In freshwater pearls exotic colors are easy to produce and in small sizes they will all go for about the same price whether the color is white, pink, orange, or violet. In larger pearls, especially the American grown pearls, the pinks will grab the highest price. Pearl colors should be chosen to go with the wearer's complexion and wardrobe. Of course pearl lovers may have a selection of strands in different colors.


Luster is the beautiful aspect of the pearl; it is what makes the pearl different from other gem materials. The better the luster of the pearl the more light it reflects. Luster is another important factor in valuing. Obviously the higher the luster, the higher the price if all other factors are equal. The nacre layers must be adequately deep to give proper luster. The orient of the pearl refers to the quality of reflection off the layers of nacre.

Cultured pearls that have only been left in the oyster a short while, less than a year, will not have thick nacre layers and will lack luster. These are called "young pearls" in the trade. In lower quality cultured pearls you can see the concentric black lines of the mother of pearl bead through the nacre if you examine them closely, especially under a strong light source.

When you are buying pearls it is best to compare strands side by side to compare color and luster. Differences are quite easily spotted this way. Be sure to compare them on a white or neutral gray background to accurately see color differences. While you are examining strands of pearls, roll the strand on a flat surface and look for pearls that "blink"; "blinkers" are pearls with uneven and thin nacre layers; the blinking part is what can be seen of the mother of pearl bead underneath, which is easily visible. The pearly luster is absent and the pearl appears dull. Often strands will have a couple of "blinkers" which are easily spotted when next to a pearl with more nacre layers.


Some pearls have pimples whether they are adolescent or more mature. Blemishes are the small spots and other visible imperfections on pearls. If there is just one small spot on a pearl that will generally be where the pearl is drilled. Small blemishes will lower the price, but may not detract from the beauty when the pearls are worn. Unsightly spots obviously detract from the overall appearance. Highly blemished pearls will sell for a lower price.


When you are choosing pearl strands look at the total length of the strand and see how well the pearls match. Size, shape, color, blemishes, and luster should be fairly homogeneous throughout the strand. See if size graduates evenly; on uniform strands the pearls when temporarily strung will start will the smallest sizes on the end and will have the largest sizes near the middle. On exotic pearls matching may not be a factor; fancy colors of freshwater pearls strands may be more interesting when they are mixed. Baroque pearl strands may also be fascinating because of the variety in shapes.

Front Strand - Cultured Pearls, Japan
Second & Third Strands - Freshwater Pearls, China
Photo by Pearl Sales Institute

Pearl strand lengths

Uniform Japanese cultured pearls under 6 millimeters in diameter are temporarily strung on fourteen inch strings. Pearls of 6 millimeters and up will be on sixteen inch temporary strands. South Seas cultured pearls will also be strung on sixteen inch temporary strands. When these are permanently strung into necklaces, about two inches are added to the length by the knots between the pearls and the clasp. Longer strands are a marriage of one or more strands. Adding pearls to a strand at a later date to lengthen it may be hard and achieving a perfect match may be impossible.

Pearl strands are generally sold in tradition lengths. A choker length is l4 to l5 inches in length. Sixteen inches is standard length for 6 millimeter pearls or less; eighteen inches is standard for pearls 6 millimeters and up. Matinee length can vary from 20 to 24 inches. Opera length ranges from 28 to 30 inches.

Treatment of pearls

The first thing that happens to a pearl during processing is that it is cleaned up (think about sleeping with an oyster for three years). Japanese cultured pearls are all processed by the growers; these are trade secrets of each company. In general they are all scrubbed and polished and bleached.

Off colored pearls may be dyed. Shades of blue, gray, bronze-brown, and blacks are commonly shades for dyed Japanese cultured pearls. If you see these colors in pearls under l0 millimeters in size, assume they are dyed. Some pearls are dyed pink to enhance the overtone. To see if a pearl is tinted pink artificially look around the drill hole and examine the blemishes closely. Dyed pearls will show a concentration of dye in these areas. Dyed pearls should not be as expensive as the same natural color.

South Sea pearls may also be dyed; if this is the case they should be cheaper than a naturally colored one the same color. Freshwater pearls may also be dyed. In most case this dyeing is obvious. When it is done to common strands of "rice" pearls, the color just does not look real. In naturally colored freshwater pearls there will usually be a variation of color of pearls on a strand and often a variation of color on each pearl. These naturally colored pearls have a richness the dyed ones lack. Ask the seller to write the origin of any unusual color on the sales slip.

In rare cases, pearls are irradiated to produce dark gray to black colors.

Ready to buy pearls

The first thing to remember when you go to buy pearls is to be sure you are examining them against a white or light gray background so you can see and judge the color. Bad pearls will look better against black than against a white background.

If you have no budget restrictions, buy the best pearls in a color that is complimentary to you complexion and clothing. But if you cannot afford a ten millimeter strand with white body color, fabulous rose overtones, mirror-like luster, no blemishes and perfectly round (somewhere in five figures U.S. dollars) you must make a decision of what to compromise. Size and shape make a great deal of difference in the price of a strand of pearls but really don't affect beauty.

For years, pearls measuring 6 1/2 to 7mm in diameter were the most popular size in this country; today, larger pearls are preferred. If you choose a pearl that is not quite round, such as semi-rounds, you will save quite a bit. A slight variation in shape isn't really noticeable when the pearls are worn. Prices on rose overtoned white pearls are the highest, but if the color is cream minus the overtones, price falls. Pearls with an obvious yellow color sell for a lot less than white ones do and these shades actually compliment certain complexions and clothing colors: some women look better in warmer toned pearls.

Small blemishes also lower the price, but if minor, may not look bad when the pearls are worn. Sacrificing luster would sacrifice the unique beauty of the pearl so that should be you last sacrifice, not your first. The wearer should choose the length of the pearl strand that will be most flattering to her body size and shape. The length of your pearls must be compatible with the types of necklines you wears. Keep this in mind if you are buying pearls as a gift for someone. Of course, more than one strand of pearls is very fashionable for the well dressed woman.

South Sea cultured pearls are available in huge range of qualities. Variations in size, color, and shape give the buyer a wide variety of prices and styles. Strands of South Sea cultured pearls will fall into the expensive to very expensive category. Single South Sea cultured pearls are very popular as pendants; the variations of size, shape and color are nearly infinite. Pieces of single pearls range from low to expensive.

Is it natural, cultured or imitation?

Natural pearls may be difficult to distinguish from cultured pearls. To be absolutely certain a pearl is natural, they are X-rayed to determine what composes the core of the pearl. Cultured pearls with thin nacre can be easily distinguished from natural pearls because the dark bands of the shell bead can often be seen through the nacre in strong light. This will not work if the nacre layer is thick. Looking down the drill hole sometimes you can see the mother of pearl bead below. This is not always possible and some pearls are not drilled.

Natural and cultured pearls can easily be distinguished from imitations since both have layers of conciolin, which feels gritty when it is rubbed against the edge of your teeth. This is the famous "tooth test". Try it! Don't be shy. Generally if you examine cultured pearls carefully you can see small blemishes and a slight unevenness in coloration or luster. In imitation pearls, color is even, blemishes are non-existent, and imitation pearls are smooth against your teeth: they flunk the "tooth test".

Care and cleaning of pearls

Pearls are one of the more fragile gem materials; they can easily be scratched and can be harmed by harsh chemicals or perspiration. Store pearls in separate containers so they will not be scratched by other jewelry. Pearls should be strung on knotted silk thread. Nylon thread is too harsh and may wear away the drill hole. Knotting accomplishes two things: it keeps pearls from wearing excessively around the drill hole and it also keeps pearls from getting lost if the thread is broken. If you wear your pearls a lot get them restrung when the thread shows signs of stretching and the pearls can move between the knots. To routinely clean pearls, wipe them off with water-dampened cotton balls. Avoid chemicals of any sort. The nacre layer is composed of calcium carbonate which is a very soluble chemical. If your pearls are really dirty, take them to a jeweler for cleaning. Avoid spraying hair spray or perfume on pearls and wipe them off if you perspire on them.

By Sondra Francis – © Gem Dealers’ Secrets – Handbook for the Gem Buyer – 1999
All rights reserved internationally. Copyright © Sondra Francis. Users have permission to download the information and share it as long as no money is made-no commercial use of this information is allowed without permission in writing from Sondra Francis.
About the Author
Sondra Francis has scoured every major colored gemstone market in the world since 1978. She was a charter member of the American Gemstone Association and served as a board member. She was a founding member of the International Colored Gemstone Association. A true gem lover, Sondra has marketed her treasures on the wholesale and retail markets.
A special thanks to Pam Dulgar, Alex Edwards, Cheryl Kremkow, Kate Kirby, Helen Mitchell, Carol Morgan Page, David Pond, Elaine Proffitt, and Ray Zajicek for their help.
Photographs: Bart Curren and ICA Gembureau ; Alex Edwards, Pearl Sales Institute ; David Dikinis

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Sondra Francis

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