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Pearls

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Pearls have been the stuff of legend and lore throughout history.  Born of adversity, prised and collected for more than 4000 years, they are the world's oldest gem.  Julius Caesar was so enamored with pearls that by Roman law only aristocrats could wear them. The historian, Suetonius, wrote that Caesar invaded Britain in 55 B.C. primarily to ensure his personal pearl supply.

What is a pearl?
A pearl is formed when a small irritant or parasite penetrates and lodges in the mantle tissue of a mollusk when it is open to collect food.  In response, it secretes a substance called nacre to surround the irritant.  The nacre builds up in layers and, after a few years, forms a pearl.  Nacre is a combination of two substances.  The first is calcium carbonate, which the mollusk forms into a mineral called aragonite. This has the same calcium carbonate used in many antacids.  In fact, hundreds of years ago, pearls would be crushed into a glass of wine to treat the royal stomach.  This is also the same substance as the mother-of-pearl lining in the mollusk's shell.  The aragonite forms a layer of prismatic crystals that surrounds the irritant.  Light passing through and reflecting off these prismatic crystals produces the iridescent colors referred to as orient.  Next, the mollusk secretes a layer of conchiolin, an organic protein that serves as an adhesive for the next nacre layer.  The orderly arrangement, total thickness and smoothness of these nacre layers determines the quality of the finished pearl.

Natural Pearls vs. Cultured Pearls

It's a bit difficult for us, living in the age of cultured pearls, to grasp how incredibly rare pearls were throughout history, because, until the late 19th century, all pearls that existed were natural.  Only the very, very wealthy could afford to own even a single pearl, let alone a whole strand.  Natural pearls are organic gems, created by a mollusk, by chance, without human intervention.  They are made up of layer after of layer of solid nacre.

Cultured pearls are created by a mollusk with the same process around an implanted shell bead.  The majority of the pearl made up of the shell nucleus, so, while the nacre is the same material as in a natural pearl, it is much, much thinner.  In fact, in very fine quality pearls, a 7mm pearl will begin with a 6.5mm starter bead, so only .5mm is nacre.  Cultured pearls can be distinguished from natural pearls through the use of x-rays, which reveal the inner part of the pearl. Sometimes, if you hold a pearl up to a strong light, you can see the starter bead inside.  You can sometimes see the nacre layer by careful examination of the drill hole.  Simulated, imitation and "faux" pearls are man-made from a variety of products, and are not the same as cultured pearls.



Cross Section of Cultured vs Natural Pearl

Cross Section of a Pearl



Kokichi Mikimoto, Father of the Modern Cultured Pearl Industry


Kokichi Mikimoto (1858-1954) was the first to successfully market cultured pearls. He began raising oysters in 1888, and by the late 1890s he had been awarded a patent on a process for culturing mabes (hemispherical pearls).  Over the next 20 years, he continued his research into culturing pearls. Using a technique developed by William Sawville-Kent and brought to Japan by Tatushei Mise and Tokishi Nishikawa, he successfully cultured whole akoya pearls and acquired a patent in the early 1900s.

Mikimoto embarked on a campaign to introduce cultured pearls to the world, and essentially created the cultured pearl industry.  He received numerous honors and awards from his native Japan. Mikimoto died in 1954 at the age of 96.  Mikimoto is still the world's premier cultured pearl brand.  His effect on the modern pearl industry cannot be overstated.

Saltwater Cultured Pearls
Akoya pearls are produced by Akoya oysters, Pinctada fucata martinsii.  Akoya production once were exclusively grown in Japan, but the Chinese have nearly taken over the Akoya market.  Depending on the size of the oyster and the size of the starter bead, they can be between 2-10mm, but are rarely larger than 10mm.  Akoya pearls are known for their high lustre and rich colour which can range from pure white to cream, pink, green, silver, and gold. While usually of natural colour, Akoyas are sometimes dyed black or other colours.

South Sea pearls are large pearls, most more than 10mm, produced by much larger Pinctada maxima in the warm waters of Australia, Indonesia and the Philippines. The average size is 11-14 mm, and pearls over 16 mm are considered quite large.  White South Sea pearls are produced by Silver-lip oysters, and golden pearls are produced by the Gold-lip oyster.  South Sea pearls are cultivated longer and therefore have thicker nacre than Akoya pearls, and therefore are often less perfectly round.  Fine quality South Sea pearls are rare and expensive, but because of their thick nacre will last for generations, if cared for properly.

Black South Sea pearls are naturally black pearls come from Tahiti, the Cook Islands and French Polynesia, and are produced by the Black-lip oyster, Pinctata margaritifera.  Sizes start at 8 mm, with 11-12 mm being the average, but they have been known to grow as large as 20mm.  They range from grey to black, but their colour combines dark blue, dark green and violet tones, with peacock green being the most popular. Some Black South Sea pearls are treated to produce fine quality "chocolate" pearls.

Freshwater Pearls

These are grown in mussels that live in lakes and rivers. They are cultivated in many countries, with the leading producers being the United States, China and Japan.  Most freshwater pearls are non-nucleated, which means they do not start with an implanted shell bead as do saltwater cultured pearls, but rather with a tiny piece of mantel tissue, and are therefore nearly all nacre. As many as 10 to 50 pearls can be cultured in one mussel.  Freshwater pearls produced in this manner are usually either shaped like grains of rice or oval-shaped.

Round freshwater pearls are now being produced in China with different type of implant technology using a starter bead.  Chinese freshwater pearls are routinely treated to produce a variety of colours, including black, and care should be taken not to mistake treated freshwater pearls for their much more expensive, naturally coloured saltwater counterparts.

American freshwater pearls start with a shell bead nucleus, like saltwater cultured pearls.  Most are grown in the Tennessee River, in the same type of mussel whose shell is used to make starter beads for saltwater cultured pearls.  American freshwater pearls are left inside the mollusk for 3-5 years, as opposed to 12-18 months for most saltwater pearls, and therefore have a thicker coating of nacre. These pearls are never enhanced, so they have variations in colour, shape and surface perfection, as do natural pearls.


Other Unusual Pearls
Abalone are actually sea snails, and have long been a valuable food source every area of the world where they are abundant.  Some of the larger species are now threatened, and abalone is now mostly considered a delicacy.  The thick, inner layer iridescent nacre, or mother of pearl, that lines the inside of the shell varies in colour from silvery white, to pink, red and green-red to deep blue, green and purple, and is used in inlay and shell jewellery.  Abalone pearls form in a variety of shapes, and some of them are even hollow.  Abalone pearls are very rare because the majority are natural, although there is an emerging market in cultured abalone mabe pearls.

Conch pearls are natural (non-nucleated) pearls harvested from Queen conch in the Caribbean and the Gulf of Mexico. Conch, like abalone, is also in great demand for its meat, and its shell is used for decorative purposes, including carving cameos.  Conch pearls come in a range of hues, including white, brown, orange and many intermediate shades, but pink is the most desirable colour.  The highest quality pearls have a distinctive 'flame structure' that gives the appearance of a fire burning on the surface.  The effect is a form of chatoyancy, caused by the interaction of light rays with the microcrystals in the pearl's surface.  Conch pearls are rare; about one in every 10,000 to 15,000 opened will contain a pearl.

Pearl Grading

At present, there is no unified industry grading standard for pearls as there is with diamond grading.  Mikimoto developed a letter grade system for its pearls and other companies have adopted a similar system, but there is no standardised definition of those grades.  When shopping for cultured pearls, be sure you understand each company's grading standards, and take a few minutes to educate yourself on the following factors that affect pearl quality and value:

Lustre and Orient

Lustre is the quantity and quality of light reflected from the surface or just under the surface of a natural or cultured pearl.  Orient refers to the iridescent colours on the surface of some natural and cultured pearls.

Nacre Thickness and Quality

Nacre thickness is the depth of the nacre layer on the bead nucleus.  The quality and thickness of the nacre affects all other aspects of a pearl's quality, especially its life span.  Pearls with a thin nacre layer will deteriorate much more quickly.

Surface Perfection


The pearl's surface is like its skin; it can have blemishes.  Almost all pearls will have some type of surface imperfections, but they should be small and not detract from the pearl's overall beauty.

Shape

Shapes range in descending order of value from round to semi-round, off-round, oval, drop and baroque.  Shapes from round to drop are symmetrical, while baroque denotes a pearl that is completely asymmetrical or free-form.

Size

Cultured pearls are measured by their diameter in millimetres, unlike natural pearls, which are sold by weight. They can be smaller than one millimetre in the case of tiny seed pearls, or as large as twenty millimetres for a big South Sea pearl. The larger the pearl, generally the more valuable it is.  Strands are listed as a range, such as 5 1/2-6mm, because most strands will vary slightly based on how many pearls are in the strand.  They will be strung with the larger sizes in the centre and graduated toward the ends.

Colour

Colour plays an important part in the value of cultured pearls.  Natural colour pearls are more valuable than colour treated ones, a fact should be reflected in the price.  Pearl colour has two aspects:  body colour and overtone.  Body colour refers to the primary overall colour of the pearl, such as white, cream, yellow or black.  The overtone is a secondary colour, or tint, usually pinkish, greenish, silver or blue.  Pearl colour refers to a combination of both body colour and overtone.

Matching

Matching is very important to the overall beauty and value of a finished piece.  Because each pearl is different, it can take years to accumulate a perfectly matched string of pearls.  Pearls should be closely matched in all aspects, not just size.

Pearls Have a Life Span


Diamonds may be forever, but, unfortunately, pearls are not.  Unlike diamonds, pearls are organic gems that have a life span of roughly 150 years.  A pearl's life span can be shortened by improper care and storage. For more complete information on pearl care, visit our Jewellery Care page.

-By Cynthia B. Reuschel RGA


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