The pearl is the only gemstone which is grown inside of a living organism. Pearls are formed
within oysters or mollusks when a foreign substance (most often a parasite - not a grain of sand)
invades the shell of the mollusk, entering the soft mantle tissue, and picking up epithelial cells.
In response to the irritation, the epithelial cells form into a sac (known as a pearl sac) which
secretes a crystalline substance called nacre, the same substance which makes up the interior
of the oyster's shell, which builds up in layers around the irritant, forming the pearl.
Natural pearls have always been extremely rare and valuable. Because the layers
of nacre tend to maintain the irregular shape of the original irritant, natural pearls
which are round or spherical in shape are even rarer still, and are highly prized.
Most natural pearls are irregularly shaped.
In a completely natural state, only a very small percentage of oysters will ever
produce a pearl at all. Of the pearls which are produced, only a handful will develop
to a desirable size, shape, and color; and only a small fraction of those will be
harvested by humans. It is commonly assumed that only one in ten thousand oysters will naturally
produce a gem quality pearl. As pearls have been a prized gem by much of the world's
population for thousands of years, this need has led to the development of cultured pearls.
In the late 19th and early 20th centuries, however, several Japanese researchers discovered a
method of producing pearls artificially. Essentially, the technique involves inserting a foreign
substance, or nucleus, into the tissue of the oyster or mollusk, then returning the creature to the
sea and allowing the resulting cultured pearl to develop naturally. This practice was quite
widespread harvesting Mabe pearls
These cultured pearls could now be produced in sufficient quantities to make them available to
virtually anyone.
The cultured pearl industry has now far surpassed that of the natural pearl industry. Although a
market still persists for pearls gifted to us by nature, these pearls are becoming more and more
difficult to find, with rare full strands being auctioned for hundreds of thousands of dollars.
Today, purchasing a pearl necklace from nearly any store in the world means purchasing a
strand of cultured pearls. Pearl Formation
A pearl is formed when a small irritant or parasite penetrates and lodges in the mantle tissue of a
mollusk. In response nacre is secreted. Nacre is a combination of crystalline and organic
substances. As nacre builds up in layers, it surrounds the irritant forming a pearl.
Natural Pearls vs. Cultured Pearls
Natural pearls are pearls formed by chance. Cultured pearls have been given a helping hand.
Today, nearly all pearls are cultured. By inserting a foreign object into a mollusk, pearl farmers
can induce the creation of a pearl. The same process of pearl creation takes place. The
difference is that in this case, the inducement is intentional.
Cultured pearls can be distinguished from natural pearls through the use of x-rays, which reveal
the inner part of the pearl.
South Sea pearls are among the largest commercially harvested cultured pearls in
the world. The average size of a South Sea pearl is 13mm, with most harvests
producing a range of sizes from 9mm up to 20mm.
The South Seas lie between the northern coast of Australia and the southern coast of
China. These waters are the native habitat of the large oyster, the Pinctada maxima. This oyster
grows up to 12 inches in diameter, and can be nucleated with a much larger bead than other
saltwater oysters such as the Akoya.
There are two varieties of Pinctada maxima: the silver-lipped and the gold-lipped. The two are
distinguished by the coloration of the outer edge of the interior. This shell is also known as
mother-of pearl and is responsible for the coloration of the cultured pearls produced.
The South Sea oyster will only accept one nucleation at a time. The oyster is nucleated when it
is only about half developed, from 4.7 inches to 6.7 inches in size, or about 24 months old.
Although the South Sea oyster will only handle one nucleus at a time, this oyster (like the
tahitian pearl producing Pinctada margaritifera) can be nucleated up to three times over the
course of many years.
There are four reasons South Sea pearls can grow to such large sizes dwarfing many of their
saltwater pearl counterparts. The reasons consist of: the large size of the Pinctada maxima, the
size of the implanted bead, the length of time the pearl is left to grow in the oyster, and the
oyster’s environment. Due to the size of the oyster it is able to accept a large bead. Because of
this same reason the South Sea oyster deposits nacre around the nucleus at a much quicker
rate, especially in warm water which speeds the oyster’s metabolism. The South Seas are also
extremely clean, and filled with plankton – the Pinctada maxima’s favorite food source. The
clean waters and abundant food supply also speeds the nacre production. The growth period for
South Sea pearls is also substantially longer than that of the Akoya
South Sea pearls have several distinct characteristics that are unique to this gem. The nacre is
unusually thick, ranging from 2-6mm compared to the .35-.7mm of an Akoya pearl. South Sea
pearls also have a unique, satiny luster that comes from the rapidly deposited nacre and warm
waters of the South Seas. South Sea pearls also have a subtle array of colors, typically white,
silver, and golden, that are rare in other pearl types.
Tahitian pearls are produced by the black-lipped oyster (Pinctada margaritifera)
in the islands of French Polynesia. The oyster itself is quite large -- sometimes
over 12 inches across and weighing as much as 10 pounds -- which often results
in much larger-than-average pearls. The pearls are unique because of their
natural dark colors. Most "black" Tahitian pearls are not actually black, but are
instead silver, charcoal, or a multitude of colors with the dominant color being green. Truly
black pearls are extremely rare.
The black-lipped oyster's mother-of-pearl inner shell is also extremely attractive. By the early
part of the 20th century, before conservation and repopulation efforts began, the oyster had
almost been hunted to extinction for its shell alone.
Although Tahitian pearls are thought my many to be solely a product of Tahiti this is in fact not
Tahiti is the commercial center and trading hub for the bulk of the industry, however Tahiti does
not have any pearl farms located on the island. The farms are instead scattered throughout
French Polynesia, as far east as the Gambier Islands, and beyond French Polynesia to the west
into the Micronesian Islands. Australia, the Seychelles and Vietnam have all produced black
pearls as well.
Tahitian pearl farming has much later commercial origins than its other cultured pearl cousins.
the early 1960's a man by the name of Jean-Marie Domard began experimenting with the
Pinctada margaritifera using Japanese culturing techniques. In 1962 Mr. Domard successfully
nucleated 5000 oysters, and after 3 years harvested more than 1000 high-quality Tahitian pearls.
Keshi pearls are formed when the oyster rejects and spits out the implanted
nucleus before the culturing process is complete, or the implanted mantle tissue
fractures and forms separate pearl sacs without nuclei. These pearl sacs eventually
produce pearls without a nucleus.
Keshi may form in either salt water or freshwater pearls. They are generally small in size and,
because there was no nucleus to guide the ultimate shaping of the pearl, their shapes vary
Keshi come in a wide variety of colors, and tend to have high luster and even rare orient. This is
due to their solid-nacre composition.
Because the implanted nucleus of the pearl has been expelled by the oyster, the resulting keshi
pearl is 100% nacre. This gives it an especially lustrous and shimmering surface quality. Most
keshi, in fact, have a greater luster than even the best-quality cultured pearls. The fact that keshi
pearl are solid nacre does not, however, give them the classification of natural pearls. This is
because keshi are a biproduct of the culturing process, not a natural occurrence.
Keshi pearls, especially Tahitian and South Sea, were once quite the bargain yet beautiful and
unique pieces. Today Keshi pearls are much more rare. This is because Tahitian and South
Sea pearl farms are now x-raying oysters to determine whether or not the nucleus has been
expelled. When a nucleus-free oyster is found they are then re nucleated before a keshi has time
to form. This practice has made keshi pearls much more of a rare find than they once used to be.
The word keshi means "poppy seed" in Japanese, and these pearls are often also referred to as
"poppy seed pearls."
Although the traditional source of pearls has been oysters which live in saltwater,
mollusks which live in freshwater lakes and rivers can also produce pearls. China
has harvested freshwater pearls in the form of maybe since the 13th century, and
is now the world's undisputed leader in freshwater pearl production. The first
record mentioning pearls in China was from 2206 BC. The United States was also a
major source of natural freshwater pearls from the discovery of the New World through the 19th
century until over-harvesting and increasing pollution significantly reduced the number of
available pearl-forming mussels.
Generally speaking, freshwater pearls are not as round as saltwater pearls, and they do not have
the same sharp luster and shine as akoya pearls. However, they appear in a wide variety of
shapes and natural colors, and they tend to be less expensive than saltwater pearls, making
them very popular with younger people and designers. As freshwater pearls are solid nacre, they
are also quite durable, resisting chipping, wear, and degeneration.
Freshwater pearls differ from other cultured pearls in that the great majority are not bead-
Freshwater mollusks are nucleated by creating a small incision in the fleshy mantle tissue of a 6
to 12 month old mussel, and inserting a 3mm square piece of mantle tissue from a donor
mussel. Upon insertion the donor (graft) tissue is twisted slightly, rounding out the edges. What
happens after this point still speculation. Some believe that this tissue acts as a catalyst in
producing a pearl sac thus making the 'nucleation' actual 'activation', others believe the tissue
molds with the host to create a pearl sac, while still others maintain the tissue is the actual
nucleus. Although it is said that a freshwater mollusk can withstand up to 25 insertions per valve,
it is not common industry practice to perform only 12-16 insertions in either valve, for a total
production of 24-32 pearls. The mollusks are then returned to their freshwater environment
where they are tended for 2-6 years. The resulting pearls are of solid nacre, but without a bead
nucleus to guide the growth process the pearls are rarely perfect round.
The Japanese have a distinguished history of culturing freshwater pearls as well. Lake Biwa was
once world renowned for producing high-quality freshwater pearls produced by the Hyriopsis
schlegeli (Biwa pearly mussel) mussel. However, in the mid 1970's pearl farming all but came to
a halt due to pollution in this lake that was once synonymous with freshwater pearls. The
Japanese tried once again to farm freshwater pearls in Lake Kasumigaura in the last decade,
utilizing a bead-nucleated hybrid mussel (Hyriopsis Schlegeli anadonata/plicata hybrid
mussels). The resulting pearls have been quite large and unique. The Kasumiga pearl industry
had a very short life span, however, with production ceasing in 2006. The industry is once again
a pollution fatality of Japanese industry. The remaining Kasumiga pearls are exclusively sold by
the Belpearl pearl company.