There are 6 main factors to keep in mind when determining a pearl's quality, value and ultimately the price of the pearls:
Nacre, Luster, Surface, Shape, Color and Size.
Nacre:
Nacre is the smooth surface that gives the pearl its beauty. When an irritant enters the oyster or, as in the case of cultured pearls is placed inside the oyster, it responds by coating the irritant with layers of nacre. The thicker and smoother the nacre the more valuable the pearl. Good quality Akoya pearls should have a nacre thickness of about 10-15% of the diameter of the pearl - in comparison Tahitian pearls may be up to 50% nacre.
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Luster:
This is the intense glow that comes from within the pearl, which is produced by light entering the pearl and reflecting back through the layers of nacre. The quality of the luster is directly related to how even and smooth the layers of nacre are. You should be able to see your reflection on the surface of a pearl with good luster. A pearl with no reflection or a dull color is of poor quality.
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Surface:
With pearls the cleaner the surface the more valuable it will be. A good quality pearl will have a few blemishes or marks - of course a pearl is from mother nature and few minor blemishes should be expected on all but the finest strands.
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Shape:
A perfectly round pearl is the most sought after and the most rare of cultured pearls. So rare are round pearls that only 5-10% of a pearl farm's harvest will be even and round. The rest of the harvest will vary from semi-round pearls to asymmetrical baroque pearls.
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Color:
Color does not greatly affect the price of pearls as it is mostly a matter of taste - When choosing a color a general guideline is skin tone. Many women with fair or light colored skin feel rose(pink) overtones look best. While women with dark skin, olive skin or that tan easily find black or cream overtones look best.
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Size:
Pearls can range in size from 1mm seed pearls to huge 20mm South Sea pearls. Cultured pearls of 6 - 7.5mm are the most common, and above this size the price jumps upward rapidly with each half-millimeter from 7.5mm up. To date the largest pearl recorded is a 26.95mm baroque south sea pearl.
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