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Basic Information About Pearls
Created naturally by living creature over many years, every pearl is unique in its color luster, size and shape.
The pearl is not produced by the high temperatures and pressures in the depth of our planet like other gems. A pearl is the lustrous, hard and smooth round mass created inside all bivalve mollusks but the only pearls prized as gem quality are in mollusks that produce them with "nacre."
The pearls is produced when a foreign body enters the mollusks (shellfish) between the mantel and the shell. The mollusks cures the aggravation or irritation by coating it with a substance called nacre or mother-of-pearl which keep growing into a pearl.
Pearls are valued by size, shape, flawlessness, color and luster
To correct a misconception, pearls are obtained from the pearl oyster (Pinctada) not the edible one you have in a restaurant.
The pearl oyster, abalone and great conch that are found in the Gulf of California are all sea creatures and therefore produce salt-water pearls.
Freshwater pearls are produced by mussels.
Pearls are measured by weight in grains, there are 4 grains to the carat. That is the same carat by which all gems are weighed. However it is not so uncommon now for pearls to be quoted in millimeters.
The ideal shape for a perfectly round though natural pearls are quite often imperfect. Cultured pearls however are usually round due to the way they are formed. Odd shaped pearls are called baroque and are commonly in the freshwater variety.
Only three flaws will reduce a pearl’s value by 50%. Sometimes these marks are hidden by the drilling of the bead.
Pearls come in a variety of colors and shades depending on the source. Colors vary from silver-white through shades of cream, light and deep gold, peach and pink. Sometimes an unusual bronze, blue or green color appears. Perfect white pearls are the most sought and expensive specimens.
Pearls are normally white or bluish-gray but can be pink or black. The most highly valued are oriental pearls because of their iridescence, translucence, shape and deep pearly luster created by diffraction and interference.
This is known as the ‘orient’ of the pearl and is what gives it its unique beauty and value. Also termed iridescence it is caused by refraction of light through the many layers of nacre.
Pearl of Lao Tzu
The largest known pearl is is the Pearl of Lao Tzu (or Pearl of Allah) weighing 14 pounds 1 ounce (6.37 kilograms).
It was found inside a giant clam in the Philippines in 1934 by a Filipino diver.
Natural pearls and cultured pearls
The number of natural pearls available in the world have been reduced over the last 150 years, the constant demand for natural saltwater pearls have led to the overfishing of the natural pearl beds and many of them were lost for good. For instance, the Angel-wing pearls from the Mississippi River and nearby lakes were very popular with Art Nouveau jewelers in the 1900s but these days they have all but disappeared from the water that is one the reason why the natural pearls have become very expensive.
As the supply of natural pearls decrease, the need to develop affordable cultured pearls becomes essential. The idea of accelerating the process was not new, it was first created by the Chinese in the 12th or 13th century, the Chinese began inserting objects into freshwater mussels in the thirteenth century. In the late 1890s in Japan, Kokichi Mikimoto started the commercial production of cultured pearls after many years of experimentation.
The process, in the simplest terms consist of implanting a bead of mother-of-pearl (usually between 6 and 13 mm in diameter) between the mantle and the shell of a live oyster in a laboratory and returning it to the oyster bed to grow. The bead or nucleus, stresses the oyster which to isolate the irritation, deposits nacre over it, creating a pearl.
The length of time that they are left to grow determines the eventual quality of the final product. Several years ago they would be left for two or more to grow their coating of nacre but commercial pressure has reduced the growing time to six to eight months. Consequently many cultured pearls have a very thin layer of nacre that tends to wear away or peel off. Better quality pearls sourced from the South Seas are still available but at a price.
Nowadays 90% of the pearls are sold cultured and Japan is now the main marketing center for the gem.
Wallis, K. 2006. Gemstones: understanding, identifying, buying. Woodbridge, Suffolk, Antique collectors club.