 Pearl Facts
CHEMISTRY CaCO3 (aragonite, the outer layer) about 83 - 86%, conchiolin 10 - 14%; water 2%.
CRYSTALLOGRAPHY Aragonite is orthorhombic, crystals oriented radially
SPECIFIC GRAVITY 2.6 - 2.78
REFRACTIVE INDEX 1.53 - 1.69
HARDNESS 2.5 - 4.5
WEARABILITY Excellent
CLEAVAGE None
ENHANCEMENTS Commonly dyed
HEAT SENSITIVE Yes
CHEMICAL SENSITIVE Yes
SPECIAL CARE Avoid dry heat and all chemical substances, including perfume and other cosmetics.
An intricate system of hierarchy distinguishes pearls from another and determines their worth. Luster and size are two significant factors involved.
Luster
Luster refers to the light reflected off the internal layers of nacre. It’s quality depends on the finesse and evenness of the layers. It is a combination of outer brilliance and a deep inner glow. The deeper the glow, the more perfect the surface area and shape, the dearer they are. A quality pearl possesses a bright luster, reflecting the high mirror-like quality which allows you to see your reflection clearly on the surface. This is only relevant to salt water pearls (like the Akoya) which have a shell bead at their core. Low luster in pearls is often associated with thin nacre. The foggier your reflection, the lesser the nacre, the less valuable the pearl. If the pearl has been prematurely harvested, resulting in a thin nacre coating, the bead at its core may be visible and the nacre can split or flake. Dark nacre does not reflect light in the same manner as the white nacre. The best way to learn the luster potential of a black pearl is compare black pearls ranging from very low to very high luster. The higher the pearl’s luster, the higher its quality, the greater it’s worth and value!
Nacre Thickness
Nacre is the natural mucus-like substance that the mollusk secretes to protect its sensitive flesh from irritants such as sand, shell fragments or implanted beads. This is the same beautiful iridescent material that lines the inner surface of the oyster shells, aptly named mother-of-pearl. As a rule, the thicker the nacre, the higher the quality of the pearl. Nacre thickness is one of the principal reasons for wide price differences between seemingly identical sets of pearls. Optimally, ensure that the nacre thickness is at least between 0.30 to 0.50mm thick.
Harvesting
Just like a human infant needs an average of nine months in the mother’s womb to grow naturally, saltwater pearls need to be tended for two to three years to grow a thick enough nacre before they may be harvested into a bright, luminous creation of the sea Goddess. Freshwater pearls, on the other hand, need twice as long as saltwater pearls to reach the same size and nacre. This is because they lack human interjection and are not nucleated with a shell bead.
Orient
Orient reveals the manner by which light is reflected off the various layers of nacre. If you hold the pearl in front of a neutral or white background, you can see that as the light penetrates the surface of the pearl, it illuminates the many layers of nacre allowing you to observe these layers and their color. The Orient may be deemed as the very soul or inner glow of the pearl.
Size
The size of a pearl is determined by the age of the oyster which gave it birth and the location where it was grown. The more mature the oyster, the larger the pearl. In pearls, size is described in terms of their diameter, measured in millimeters (mm). The measurements are generally rounded to the nearest half or whole millimeter. One millimeter is about 1/25 of an inch. In a strand of pearl necklace, a range of 1/2 millimeter is usually indicated (i.e., 7 - 7 1/2 mm). Sometimes, a few of the pearls might fall slightly below or above the size indicated. Often, the smaller sizes are nearest to the clasp and the larger pearls are located in the front of the necklace. Naturally, the size of a pearl is significant in determining its price. The bigger the black pearl, the more expensive it is. Size tends to have the least effect on price in sizes below 5 mm. However, the price of pearls (especially round pearls) sharply increases when the size of the pearl exceeds approximately 7mm. This is because the longer the pearl is within the mollusk, it has a greater chance of dying of disease, of losing its shape or blemishing. A 1-mm increase in the size of a medium-quality pearl can increase its price by almost 200%! The size of non-round pearls, are expressed in terms of their greatest width and length. Wild pearls were often not round; a variety of shapes can deliver more pearls for your money!
Shape
Historically considered as a symbol of the moon, round has been considered the most valuable shape for a pearl. However, as few pearls are perfect spheres, the most well known valuable pearls are not often round. The larger a pearl grows, the more likely it is for it to be off-round in shape (which is why very large round pearls are precious and rare). Although cultured, the process occurring within the farmed shell is still a natural phenomenon. Pearls come in baroque, button, mushroom, barrel, acorn, tear-drop and pear shapes. The rounder (more rare and valuable) pearls are normally used in rings, necklaces and earrings, while the other shapes are more often used in broaches and pendants. Shape is subjective, but as a simple test hold a strand or necklace about two feet away and turn it in your hands. See for yourself, whether the pearls look mostly round. If you need to save on the price of pearls, it would be best to compromise on the shape factor.
Surface Quality
The pearl’s outer surface is examined to determine its texture, as well as the type and number of blemishes. Most natural pearls will include very tiny dimples known as ‘birth marks’ or ‘beauty spots’ which are sometimes imperceptible to the naked eye. It is these beauty marks which give the pearl its unique character and personality and distinguishes it from imitation or faux pearls. Unacceptable blemishes include holes (more than tiny dimples), surface cracks and flaking nacre. The smoother the pearl surface, the higher its value.
Colors
Each of the 300 prevalent species of mollusk creates a different color pearl; these include white, cream, yellow, orange, green, blue, rose, gold, silver, brown and rarely black. Tahitian Black Pearls range from pale silver to dark black. Generally the darker the black pearl, the more valuable it is. The finest black pearls often possess shimmering hues of iridescence which create exquisite colors including pink; blue, peach; copper; gold, silver, turquoise blue; sea green; burgundy; indigo; purple; lavender; canary; cranberry; peacock green to a deep midnight black. These hues or overtones may be present in a variety of combinations, such as the feathers on a peacock, enhancing the pearl’s appearance and raising its value. Black pearls also have a wide range of body colors--black gray, blue, green, copper brown. Colors can be adjusted by adding certain chemicals in the waters where the pearls are farmed.
Different shades in a Tahitian black pearl result from the decomposition of light as it passes through layers of pearl, which act as a prism. The various layers break up the light much the same way as when light passes through a raindrop creating a rainbow. The significance of color in a pearl is a matter of personal preference and skin tone. If the color of a dress or blouse suits you, then that shade of pearl probably will too. Large round black and gold south sea pearls are prized, because they tend to suit every color of clothing or complexion.
Matching Pearls
If you are buying a good quality round pearl necklace, don't just try it on for size. Examine it carefully. A sixteen-inch necklace of 7mm pearls will include about 50 pearls. Larger 17-inch pearl necklaces hold about 37 pearls. See how well are they matched in shape, size, and luster? Turn the necklace around and see how it looks from different angles?
Necklace Lengths
- Choker: 14-16 inches
- Standard: 16 inches
- Princess: 17-19 inches
- Matinee: 20-24 inches
- Opera: 28-36 inches
- Rope: 40 plus inches
Earrings
The most popular sizes for stud earrings are between 6mm to 8mm.
Bracelets
For 'average' wrists, the most common length of bracelet is 7.5 inches.
Criterion for Rejection of Pearls
As organic creations of the Goddess of the Seas, flaws or blemishes are natural occurrences in pearls. Therefore, it is not the presence of flaws that matters. Rather, it's the type, quantity, and prominence of the flaws that makes a difference. When both the beauty and durability of the pearl are compromised with chunks of missing nacre, then the pearl is considered unacceptable.
Pearls are graded and valued on the basis of how they look to the naked eye, not under a gemologist’s magnifying glass. The GIA (Gemological Institute of America) takes this into consideration by defining "flawless" category for pearls on a strand as: "Most appear blemish-free to the unaided eye." However, the following criterion may be used for rejection of pearls:
- Milky loss of normal pigmentation marks over 25% of the pearl surface.
- Dull skin due to lack of luster, less than 0.08 MM
- Deep (and/or light) imperfections over more than 60% of the surface area.
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