March 1998


This is the first in a series of pearl quality factor discussions designed to help you explain these popular and precious gems to your customers

by Devin Macnow Cultured pearl Information Center

For cultured pearl experts, luster is perhaps the most important indicator in evaluating cultured pearl quality. Luster is what separates the inferior pearl from the superior and the ordinary from the extraordinary. Luster is what many experts term the heart and soul of the sea-grown gem. Throughout history, this unique luster has separated pearls from all other gems. Early man, captivated by this mysterious sphere born from the ugliest of all sea creatures, likened the luster of a pearl to that of the shimmering moon. In fact, pearls were once believed to be teardrops of the moon that had fallen into the sea only to be swallowed by oysters.

Though we're no longer subject to such fanciful beliefs, the luster of the pearl still captivates. For the layman and jewelry novice, the luster of a pearl can best be described as a combination of a high, reflective sheen on the surface of a pearl combined with an almost three-dimensional glow that seems to emanate from within the heart of a pearl.

Luster, in more scientific terms, is the reflection and refraction of light as it passes through the layers of aragonite crystals (often referred to as nacre) that comprise a cultured pearl. The intensity of luster is determined not only by the amount of these crystals but also by the specific geometric pattern in which they are secreted upon the nucleus by the oyster.

Many factors play upon nacre secretion and these ultimately determine the intensity of luster. The health of the oyster, the water temperature of the host environment and the level of nutrients available to the oyster in that environment all play a vital role in creating a pearl with superior luster.

Though the intensity of a pearl's luster can be an indicator of nacre thickness, and thus determine the durability of a pearl, this correlation is not always true. In some cases it is possible for a cultured pearl to have a very thick coating of nacre and still have a mediocre luster. Again the formation of nacre crystals plays an important role in luster. Sometimes when nacre crystals are in a very loose formation they do not have the ability to refract and reflect light in the same manner as a pearl with very tightly packed nacre layers. This phenomenon sometimes occurs in pearls grown in warm water.

For the average person, evaluating the luster of a cultured pearl is not rocket science. Luster can be judged easily by the naked eye and without any equipment. Pearls with high luster have the ability to sharply reflect images around them, almost like a mirror. In addition they always display the characteristic depth or three-dimensional glow and a subtle display of different surface colors (sometimes referred to as orient) that is so prized among high-quality pearls. Pearls with low luster often look dull, monotonous, chalky and lifeless.

As for pricing, pearls with high luster account for only 8% to 10% of all cultured pearl production in any given year so they usually command premium prices. With all other factors such as surface, shape, color and size being the same, a medium-luster 7mm pearl will cost about 30% more than a low-luster pearl of the same size. A pearl with high luster will often run 60% to 70% higher than a cultured pearl with low luster.

For anyone who has ever seen a high-luster pearl, it's easy to appreciate the value and mysterious beauty captured in the gem. For without luster, a pearl is simply a bead without any real value or charm.

Copyright © 1998 by Bond Communications.


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