PHYSICAL AND OPTICAL PROPERTIES OF THE PEARL
The pearl is a biomineral, that is to say a rock of organic origin. It is made in a natural way by some bivalve molluscs, in the same way as the nacre that lines their shell. The pearl consists of thin concentric layers of aragonite crystals (calcium carbonate, CaCO3 formula) bound and supported by proteins. It is formed spontaneously when the mollusk reacts to the presence of an impurity or other foreign body that enters the shell (the nucleus), covering it gradually with mother-of-pearl.
White pearls are the densest (2.65 to 2.75). Under black light, the pearls develop whitish luminescence (for white) or red-brown (for black).
The pearls can be cultured by introducing a graft into the shells.
PEARL COLORS
The color of a pearl depends on three factors:
– the color: it goes from white to black through silver, gold, green, blue … It depends on the species of the mollusc producer, the composition of its environment, and the nature of the nucleus. The colors are coded by letters, each culture zone identifying a well-defined palette of hues. And for each hue, you can add a number from 00 (bright) to dark (100).
– The features: these are secondary colors that appear on the base color, in a translucent layer. Their presence is not systematic.
– The east: this is the name given to the optical phenomenon of iridescence when we speak of mother-of-pearl or pearls. The more aragonite layers are thin and numerous, the more these moving iridescence is developed.
THE MAIN TYPES OF PEARLS AND THEIR HARVEST AREAS
The abalone pear (Haliotis pie, Haliotis Kamtschatkana, mollusc also called abalone) is the most beautiful and the most precious, because its culture is not yet developed: it is therefore found in a natural state in … only one abalone out of 100,000! Hence its rarity among jewelers. Rich in color, with remarkable luster and brilliance, it is found on the west coast of the American continent, in Australia and New Zealand.
Akoya pearl, round and shiny, white to yellow, is produced in Japan and China by the oyster Pinctada Fucata.
The Tahitian pearl, produced in French Polynesia, is generally large in diameter and dark in color, from eggplant to black. The mollusk is the oyster Pinctada Margaritifera
The Pearl of the South Seas and Australia are from the Pinctada Maxima oyster (Philippines, Indonesia, Australia), they can be many colors.
Freshwater Pearls are the work of various species of mussels and are grown in China and Japan. Each mold can produce up to 50 beads at a time! Among them, the Biwa pearl comes from Lake Biwa in Japan.
Keshi pearls, highly appreciated by jewelers, are fortuitously produced alongside pearls provoked voluntarily by pearl farmers. Those of Tahiti are very famous.
Conch pearls, very rare, are not grown but found by fishermen in a shell called Lobatus Gigas.
The Melo Melo Wild Beads, in the South Seas, can measure up to 40 mm!
THE ADVICE OF OUR GEMOLOGIST: HOW TO CHOOSE YOUR PEARL?
The value of a pearl is based on several criteria: its shape, its luster, the quality of its surface, its size and its color.
-The shape: the pearls come in the following eight forms: round, semi-round, button, oval, pear, drop, baroque, and ringed.
– Luster: natural pearls often have a thicker mother-of-pearl, and therefore more durable and lustrous, than cultured pearls. The 4 categories of luster are: excellent, good, pale, weak.
– The quality of the surface is defined by 4 letters, from A (slight imperfections, on 10% maximum of the surface) to D (imperfections on 60% of the surface).
– the size in millimeters: most pearls have a diameter turning around 7 mm, but those of Tahiti and the South Seas go up to at least 18mm. The biggest pearls take 5 years to form.
– The color: according to the use that one wants to make, the choice of the color and thus the origin of the pearls will be important.
Sometimes, we find a tiny letter to qualify the pearl: “c” for classic, “r” as rare, “e” as exceptional.
METALS ASSOCIATED WITH PEARLS IN JEWELERY
Pearl jewelry is as good with silver and white gold as with yellow or pink gold.
STORIES AND LEGENDS AROUND THE PEARL
In China, in the third millennium BC, the pearl was collected as a tax payment. In Suza, Iran, we found an Achaemenid necklace with 216 pearls dating back to four centuries before Christ. Hindus say that Krishna would have gathered the first pearl in the depths of the sea, to offer it in adornment to his daughter on the day of his wedding.
Three Japanese invented the grafting process to produce cultured pearls with oysters: Kokichi Nishikawa, a biologist, Tatsuhei Mise, a carpenter, and Kokochi Mikimoto, son of a noodle seller, had the same idea almost at the same time. But by the thirteenth century, the Chinese knew how to cultivate pearls of freshwater mussels, and today they produce about 500 tons per year.
A beautiful Polynesian legend tells that the young princess Hina, on the island of Raiatea, was betrothed with a handsome young man, who offered him on the occasion of splendid pearl jewels. Happy, the girl promised to wear them only from her marriage, and in the meantime she had them guarded by armed men who watched them day and night. Despite this, a rejected suitor, Hiro, appealed to her on another subject. She had to refuse his request, and it was too much for Hiro who, seeking revenge, managed to steal the jewels and flee to the neighboring island of Huahine. The princess, weeping, sent against Hiro a huge dog with prodigious strength and flair. The mastiff hurried after the robber and rejoined the island of Huahine. Hiro hurried to bury his booty under a rock and then fled to the mountain. The dog manages to find the jewels thanks to its flair: he put his paw on the rock, and his gigantic footprint is always visible. Of course, the princess married her betrothed…
VIRTUES AND BENEFITS OF THE PEARL
The pearl is soft, tender and feminine. Like mother-of-pearl, it provides soothing and well-being; it would have positive effects on decalcification problems. Centuries ago, it was already used to treat dementia and epilepsy, as well as depression. In India it was given multiple benefits; especially against phthisis, ophthalmological problems, haemorrhages … Hindu medicine always uses powder, to revive energy, especially sexual. In the East, it is attributed virtues in connection with fertility and an aphrodisiac character.