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Body color and orient
The finer examples of black pearl will normally appear greenish, bluish, pinkish, or violetish in tones of gray through black. This appearance is actually a combination of two factors: body color and orient.

Body color can be thought of as a tonal continuum from gray to black. Orient or over-tone is the result of light entering and refracting through the alternating semi-translucent layers of aragonite (crystalline calcium) and conchiolin, a type of calcium that acts as a binder. The result is similar to the effect of oil on water. Orient is the ephemeral fuzzy glow, like sunlight through an early morning fog, that appears to emanate from and cling to the surface of the pearl.

Orient/overtone can be separated visually from body color by observing the pearl under a light bulb. The orient hue will be seen in the direct reflection of the bulb. The area surrounding the reflection will exhibit the body color. In fine black pearls this test is rarely necessary, as the orient, if present, is normally quite distinct.

It is this distinctive overtone that gives the black pearl its life and its air of mystery, and characterizes the finest of these pearls; it is the defining quality of the Tahitian black pearl.

Specific overtones are given fanciful names. Deep green is called flywing. The combination of green and pink is termed peacock; a dark-toned body color combined with pink is called eggplant. Occasionally pearls have a pure purple or pure blue overtone. Tiffany's famous gemologist G.F. Kunz (see quotation beginning this chapter) held that the green orient, or flywing, was the rarest and most valuable. Writing in 1908, he was speaking of natural black pearls. In cultured blacks, green is the most common orient color. Pink and blue come next in rarity, followed by peacock. Purple is by far the rarest and in my opinion the most beautiful of all.

Luster
Luster, the reflection of light off the surface of the pearl, is essentially the brightness of the pearl. The brighter, the better! In a fine pearl, this reflection is crisp and sharp. As quality decreases, the reflection becomes less distinct. Hold the pearl under a lamp and examine the bright reflection of the lamp on the surface of the pearl. The more distinct the reflection of the light source, the higher the luster.

The luster of the black pearl is some- what softer than the luster of the akoya or the Chinese freshwater pearl. In the relatively warm waters of the South Pacific, nacre accumulates at a much faster rate than it does in the colder waters off the coast of Japan. However, nacre that accumulates in colder water tends to be closer grained, producing a potentially higher luster than is possible farther south. The luster of both the black and white South Sea pearl is softer than that of "cold water" pearls.

Symmetry
The more perfect the shape, the greater the value of the pearl. Round is the most favored shape, followed by pear, oval, and button. Asymmetrical shapes are classified as baroque. Prices of baroque pearls can vary widely. All nuclei implanted in cultured pearls begin as perfectly round and blemish-free; however, nature plays some interesting tricks during the pearl's growth. As a result, the average harvest yields only a very small percentage of perfectly round pearls. Pearls can be found in many un- usual shapes.

Texture
Bumps, blemishes, tiny pits, or anything intruding on the pearl's surface is considered a negative. A silky flawless skin is the most desirable. Most pearls have slight imperfections; the issue is how much they disturb the eye. Dealers are most concerned with how the pearl will "face up," that is, whether imperfections will still be visible when the pearl is set. Pearls with surface cracks are almost worthless.

The rarity factor
Black and white South Sea pearls are, speaking generally, the largest of all pearls. This is a result of two factors: the size of the mollusk itself and the rate of nacre accumulation. The shellfish, due to its large size, can accept large nuclear implants and this, coupled with relatively rapid nacre accumulation, results in very large round pearls. The larger the pearl the rarer it is and the higher the price that will be asked for it.

Large mollusks can accept either a large number of small spherical implants or a very small number of larger diameters. It takes at least twenty-four months to lay down the two millimeters of nacre required to produce a fine black pearl. Thin-skinned pearls lack sufficient nacre to produce a fine luster and a distinct orient. Thin-skinned black pearls often exhibit a muddy brownish secondary hue or mask.

Since larger pearls command much higher prices, the usual grower's strategy is to produce a smaller quantity of larger pearls. With the increasing production of South Sea pearls, both black and white, this situation has begun to change. Growers are beginning to address market demand for smaller pearls. Prices for round pearls begin at 8mm. Black South Sea pearls under 10mm are very difficult to find for the reasons stated above. Prices increase at a reasonable percentage rate to 12mm. Prices for pearls over 12mm increase at somewhat larger percentages.

Above 16mm, prices become negotiable, because, at these sizes, rarity becomes an increasingly important factor in the value equation.

The spread of pearl culturing throughout its growing region is bound to affect prices. Dramatic increases in production in French Polynesia over the past decade have already lowered prices significantly. Although Tahiti has dominated the market for several decades, nascent industries in the Cook Islands and off the coast of Baja California are just beginning to challenge French Polynesia’s market dominance. The spread of the pearl culturing industry is likely to continue. The prognosis for the short term is, therefore, a continued softening of prices.

By Richard W. Wise

Excerpts from the book: Secrets of the gem trade (the connoisseur's guide to precious gemstones)