Pearls are not only the birthstone for the month of June, but are also “in” right now. Celebrities and Royalty have made pearls a red hot fashion item.
But what do you know about pearls ?
Pearls are formed inside the shell of certain molluscs or oysters as a defence mechanism against a potentially threatening foreign body or irritant.
The commonly held belief that a grain of sand acts as the irritant is in fact rarely the case.
Natural (or wild) pearls, formed without human intervention, are very rare
It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters mollusc and settles inside the shell. The mollusc, irritated by the intruder, forms a pearl sac and secretes calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being rare.
Natural pearls command very high prices.
Cultured pearls are formed in pearl farms, using human intervention as well as natural processes.
Cultured pearls are the response of the mollusc to a tissue implant. A tiny piece of mantle tissue (called a graft) from a donor shell is transplanted into a recipient shell, causing a pearl sac to be formed, and calcium carbonate and conchiolin is secreted to cover the irritant.
Sometimes a spherical bead is inserted as a nucleus.
Four types of cultured pearls.
Freshwater : Most are produced in pearl farms in Japan and China. Freshwater pearls form in various species of freshwater mussels. They are the most common type of pearl, and each shell can produce dozens of pearls.
Akoya (saltwater): Renowned for their brilliant lustre, and are produced by the akoya oyster. A bead is inserted in the oyster, and the pearl takes the shape of the bead.
Tahitian (saltwater): Sometimes known as black pearls and are grown in the black lipped mollusc. Only those grown in French Polynesia are officially Tahitian pearls.
South Sea (saltwater) : These are the largest and rarest of cultured pearls. They can take up to four years to grow.
What influences the value of a pearl?
Lustre, size, shape.
The greater the lustre and size, the greater the value. The more round the more value.
The colour of a pearl generally does not affect the value.
What about imitation pearls ?
Although imitation pearls look the part, they do not have the same weight or smoothness as real pearls, and their lustre will also dim.
Some imitation pearls are made of glass and coated with a glaze containing fish scales, and some will be made of Mother-of-pearl