At one time, all pearls were given to us by Mother Nature, most often in irregular sizes and in small quantities. In fact, many people are not aware that round pearls are nature’s exception.
In the early part of the twentieth century, a handful of Japanese inventors discovered the secret of culturing pearls in native mollusks and began producing gems of great beauty and lustre. In 1893, Kokichi Mikimoto hit upon the correct formula which became the basis for virtually all cultured saltwater pearls for ninety years. It was only after this that the business of culturing pearls took off. He introduced and marketed these gems to the world. Today, thanks to the scientific advances in the culturing process and improvements in pearl farming, the consuming public has a variety of pearls from which to choose. Now we can buy pearls in a range of colours, sizes, and shapes that was unheard of even a decade ago.
THE PROCESS OF SALTWATER PEARL CULTIVATION
The process of saltwater pearl cultivation is basically the same process that would happen naturally. However, in cultivation, man actually inserts the irritant. Kokichi Mikimoto discovered that a round nuclei cut from US mussel shells could be used as the irritant. Today a spherical bead of Mother of Pearl (called a nucleus) is commonly used as the irritant. Along with this bead, a small piece of epithelial membrane, or live mantle tissue from a donor mollusk (usually the sankaku mussel from Tennessee), is inserted into slits made into the mantle tissue of a receiving mollusk. This is very important since it is the epithelial cells of the inserted live mantle tissue that secrete nacre causing the receiving tissue to form a pearl sac. That sac then secretes layer upon layer of a iridescent crystalline substance called nacre which coats the nucleus, thus creating a pearl. Furthermore, by inserting shell beads of various sizes into mollusks, pearl farmers are now able to pr oduce pearls of different sizes.
The prepared mollusks, several hundred at a time, are placed in wire cages, and hundreds of these cages are suspended in the ocean beneath a special type of raft.
The mollusks are harvested after three to four years. The quality and durability of the pearl is mainly determined by the thickness of nacre layers built around the nucleus. The thickness of nacre is determined by the length of time a bead has spent in the mollusc. Two to three years is roughly the time it takes for the oyster to deposit about 1/2 mm of nacre on a 5 mm diameter bead. Mikimoto felt four years was the time necessary for nacre thickness to be sufficient to produce quality pearls. In fact, all other quality concerns are secondary to nacre thickness. Many farmers have slashed the culturing time from 2 1/2 years to 1 1/2 years and some to less than 6 months. Right now, short culture time, the length of time between nucleation and harvest. is the greatest controversy surrounding cultured pearls.
THE PROCESS OF FRESHWATER PEARL CULTIVATION
The process of freshwater pearl cultivation is the same as that of cultured saltwater pearl production except for one interesting difference. The Japanese discovered, at Lake Biwa, Japan, that it is not necessary to insert a shell bead nucleus to start nacre production. The freshwater mussel's mantle tissue is thick and large and covers the interior of both shells. It is within this mantle tissue, not the body of the mussel, that freshwater pearls are formed. Pieces of live mantle tissue from another mussel (the sankaku mussel) are placed into a mussel. It is the live piece of mantle tissue that triggers the pearl making process and nacre is deposited around this tissue.
The original Biwa pearls established a standard for cultured freshwater pearls. Unfortunately, population growth, along with houses, and small factories around Lake Biwa, Japan have polluted the water with untreated sewage, herbicides and pesticides that have washed into the water. The freshwater pearl crops have deteriorated. As Biwa production diminished, China filled the vacuum.
The Chinese have radically altered freshwater culturing, making saltwater and freshwater techniques indistinguishable. The new Chinese production matches and sometimes surpasses the original Biwa quality in shape, lustre and colours. They are producing unique colours of orange and peach, colours that Biwa mussels never produced naturally.
Because round pearls are nature’s exceptions, the Chinese have introduced a new type of culturing. They had learned that the placement and the shape of the inserted tissue is vital to the shape and quality of the finished pearl. All that is needed is the insertion of a piece of mantle. They are now nucleating mussels with their own tissue cultured freshwater pearls, which result in all nacre round or almost round pearls. They are even reshaping reject freshwater pearls into spheres, then nucleating mussels with them. Furthermore they are now nucleating some of their freshwater mussels with shell nuclei implants in both the creatures' bodies as well as in their mantles.There is another commercial product made by cultivation. While a mollusk is out of the water for nucleation, small plastic half-domes are glued to the surfaces inside its shell. Back in the ocean, the mollusk coats both the nucleus and the plastic domes with nacre, After harvesting, workers cut mother-of-pearl domes from the shell, fill them with epoxy, back with another piece of mother-of-pearl, and sell them as Mabe “pearls.” Actually, they are not pearls at all, but mother-of-pearl domes. Mabes are the principal commercial objects produced on shells.
Occasionally, the mollusk rejects the seed sown by the pearl farmer, but, continues to secrete nacre to grow a pearl. These rare, lustrous and interesting
