Pearls are the only gemstones made by a living creature, an oyster or a mollusk and have been around since time immemorial. The worth and popularity of a pearl can be judged by the fact that it was coveted by the ancient civilizations and even today a pearl is held in high esteem.
Pearls occurred naturally in nature, but their demand was so high that finally by the end of the 19th century, the ancient pearling trade and tradition declined as the supply of naturally occurring pearls dwindled. Since the demand for pearls did not dwindle, but far outstripped its natural supply, men lent Mother Nature a helping hand and so were born cultured pearls.
Pearls that occur naturally and are found in the sea or ocean beds are natural pearls. A pearl is formed when an irritant lodges itself in the tissue of an oyster, as the oyster cannot dislodge it; it secretes a substance called Nacre to coat the irritant. Nacre is composed of crystalline calcium carbonate and conchiolin and is secreted as translucent, very fine layers.
Over a period of a number of years a pearl is formed. Natural pearls are an accident of nature, and their occurrence is more a matter of chance and ideal conditions. That an irritant will lodge in the oyster is accidental and will result in a pearl is further compounded by chance. Insipte of such insurmountable odds, pearls do form but not in any number to satiate man’s craving of this unique gem.
To satisfy this desire for pearls were born cultured pearls. Cultured pearls form like natural pearls, the only difference being that the irritant is manually lodged in the oyster and the oysters are tended on special farms, the factors that are detrimental to pearls are reduced and all care is taken to ensure the formation of the pearl.
The grafting of an oyster or a mollusk to obtain a pearl is a precise and delicate procedure requiring trained professionals. Grafting means to implant a nucleus and a graft (which is a piece of mantle tissue of a healthy oyster) in to the gonad of another oyster. The nucleus used is a bead made from the shells of freshwater bivalves.
Two to three year old mature oysters are 12cm in length and are chosen for grafting. Oysters are usually reared in a rearing station, after they mature they are collected and stored in crates at the grafting work stations. Here the oysters are cleaned of the parasites that cling to their shells. The grafter is a trained technician who pries open the oyster with a dilator to about 1.5 cm and holds the opening with a wedge. From a healthy oyster the epithelial cells from the mantle tissue are excised, and small strips of this tissue forms the graft.
This graft is then coated over a nucleus. The nucleus is chosen depending on the size of the host oyster. In the gonad of the host oyster a small incision is made in to which the graft coated nucleus is implanted. The oyster is then closed and placed in a trough with its hinge end facing upward to avoid the spilling out of the implanted nucleus. This entire delicate procedure takes two minutes and the services of a trained grafter. Later the grafted oysters are placed in separate transparent bags which are necessary to hold any ejected nucleus. After the oysters have recuperated they are moved to oyster beds where they will be tended for 2-3 years till the pearl is formed.
The pearls are harvested in the winter season, when the metabolism of the oyster or mollusk is at a minimum, the deposition of the Nacre is hence thinner. The actual harvest begins by transferring the oysters from their oyster beds to the pearl farms. The oysters are pried open and the pearl is removed. Some species of oysters and mollusks can be re-nucleated and are sent back to their oyster beds to form more pearls. After the pearls are extracted they are cleaned of debris and then the procedure of pearl processing begins.
The processing of pearls is a laborious and lengthy procedure. Since the pearls develop in oysters, it is difficult to obtain a perfect pearl. Pearls after harvesting need to be treated, sorted and drilled before they can be used for jewelry. The raw pearls before processing are known as Hama-age and they have various grades.
A good quality pearl is known as Hana-dama, a lower grade is termed as Do-dama and the lowest grade of harvested pearl is a kuzu. Processing of pearls is undertaken in three stages by skilled technicians, an amateur can destroy the pearl.
Since pearls are formed by a living oyster, the quality of the obtained pearl is a matter of conjecture. All pearls are not perfectly formed and it is necessary to grade the pearls on a scale of the highest to the lowest. Quality of pearls is determined by six factors, the Nacre, luster, color, shape, size, and surface. Nacre is the most important consideration of quality, the thickness of the Nacre determines the durability of the pearl. Thicker the Nacre, better the pearl.
Luster is the sheen, or brilliance of the pearl. High quality pearls have a mirror like sheen; lower quality pearls have a chalky appearance. Shape, is another important factor. Spherical pearls are rare and so expensive. Pearls come in a variety of shapes, like oval, baroque, drop, button and keshi. Size also matters, bigger pearls are more expensive than smaller ones. Color of a pearl is a matter of taste. Here again white or cream colored pearls command more price than other colors.
Surface Quality refers to the smooth unblemished surface of the pearl, small flaws reduce the pearl’s quality.
Other factors which enhance the quality of the pearl is iridescence or orient, is the unique ability of the pearl to reflect and refract light into all colors of the rainbow. Make refers to the taste and judgment with which the pearl jewelry is assembled.
Pearls in jewelry are graded on a scale from AAA to A. AAA represents the highest quality, virtually flawless pearl, with a deep and rich luster, and a 95% free from surface flaws. AA represents pearls that have a high luster, and are 75% free of surface flaws. Pearls of ‘A’ quality are of the lowest grade, less luster and surface flaws are more than 25%.