Mollusks represent the second largest phylum of the animal kingdom; there are over 120, 000 different species. With the exception of the atmosphere and the coldest areas, mollusks dwell in all living spaces of the earth such as in the depth of ocean, on the shores, within springs and cavities, on trees and rocks, in the arid desert.
From ancient times, the shells of mollusks fascinated mankind and were worked into jewelry and decorative objects. The shapes of most shells reflect almost ideally the human appreciation of beauty. In reality, they are nothing more than a protection for an otherwise unprotected soft body. They represent the main characteristic of each species and serve to identify it.
Mollusks can range from tiny sizes to several meters in length.
Freshwater shells most likely developed from marine mollusks which migrated into Freshwaters during the Palaeozoic age (Devonian, 350 million years ago). Of freshwater mussels, two families have been found to produce pearls regularly. They are Margaritiferidae and Unionidae.
In principle, pearls can develop with in all types of marine bivalve mollusks. However, only mollusks belonging to the Pinctada and Pteria genera of the Pteriidae family are of importance. The Pinctada genus can be divided into Pinctada radiate, Margaritifera, Maixima and Mazatlanica.
Pearl-producing mollusks decide on pearl type.
Most farming areas have numerous small, protected bays with a certain flow of freshwater that lowers salinity and adds vegetable detritus to the plankton.
Running a farm requires a high capital investment and a certain tenacity in surmounting difficulties which regularly arise from time to time. A farmer is required to pay a lease to the government for the water area that he occupies and the leasing licence often remains in the dame family for generations. Considerably higher costs arise for buying the necessary amount of mulluscs and keeping them before and after nucleus insertion, when baskets, rafts, longlines, buoys and motor boats etc. are needed. The farms also require buildings where the implantation procedure can take place, which in itself demands a number of special instrument. The nuclei themselves, which are implanted into the soft bodies of the mollusks, constitute another important item. In addition, salaries must be paid to the grafters and to the numerous employees who are responsible for constant supervision and maintenance of the farm.
Hatchery stations: Today, nearly all pearl farms use juvenile mollusks from hatcheries. Lab provides some stations with the necessary new technologies to the breeding and advice on artificial propagation and genetic engineering methods. offer their help with the careful selection of parent animals, of which often only about 20 out of 400, 000 are suitable.
The nuclei: Mikimoto used tiny mother-of-pearl beads for his first successful cultured blister pearls. Earlier attempts had used nuclei made from clay, glass, lead, wood, silver and god, but had failed. Experience has shown since that pearls successfully grow on mother-of-peal beads only.
The shells are initially cut into strips and then into cubes, which are ground between two heavy iron plates using a polishing powder. After grinding and polishing, the beads take the shape, surface and proper size. All nuclei are divided into three categories: 1. perfectly round and white; 2. Round shapes but colored strips are possible; 3. Off round shape, colored, sometimes with holes on the surface;
The quality of a nucleus, above all its surface, determines the quality of a cultured pearl. The holes and scratches on surface of the nucleus leads to the blemishes on the surface of the pearl. If the nucleus is not perfectly round, the peals will also not be round. Difference in the diameter of the the spherical shape of a nucleus should not exceed 0.5-0.8mm.
Nucleus insertion: the implantation of a nucleus is the first stage in the pearl culture process. Operations may tale place over the whole year, but the time between May and October is considered the most suitable. There is a standard practice that for the implantation, two and even one year old mollusks are suitable, it is rare for animals aged over two years to be used. The work of implantation demands a high degree of concentration and technology, which decide on the mortality of animals. For instance, the shell is damaged, the animal will promptly focus on the repair of the injury and valuable energy which is needed for the growth of the future cultured pearl will be lost.
Formation of cultured pearl
The ectoderm (epithelium cells) is make up of rounded cells, loosely connected to each other, which will easily separate when stimulation comes form the outside. The separation process takes place faster if the piece of tissue has been separated from the rest of the mantle and is implanted into another type of tissue or is brought into contact with a foreign object (the mother-of-pearl inserted). The cells are replaced by new, longish ad elastic epithelium cells, which arrange themselves in a parallel alignment around the nucleus and thus form a sack. The secretion of pearly substance already starts while the pearl sack is being formed. The pearl sack grows continuously larger by cell division and surrounds the growing pearl. The slimy type of skin that is seen when the pearls are harvested is nothing other than the pearl sack.
The growth rate depends on water temperature, the time of the year and the time of the day. The water temperature varies in seasons and places. But a fact shows that 90 percent of all nacre secretion takes place between June and November in each year. Lower growth rates during the winter months lead to a smaller size of aragonites platelets, which results in a higher quality of luster. Also, plankton richly available are able to speed up the growth.
In the long run, farmers became less and less willing to accept long growth periods, even if it promised the m higher profit in the end, apart from the high costs that accumulate with each additional year, there are also higher risks involved, as the farms are exposed to constant dangers. Moreover, there is the possibility that a round pearl may develop an off-round shape, due to irregular growth, when it is left within the mollusk for more than three years.
Pearl harvesting usually takes place during the winter months between November an December, during the time that the growth rate drops and the mollusks' metabolism slows down.
When the harvest starts, each mollusk is opened and pearls are take out from the soft muscles. Pearl with an irregular pearly layer on the nucleus are discarded, and will usually account for around 10 to 15 percent of the production. Only about 15 to 25 percent of all harvested pearls are of good quality and only about 5 percent are very good. Around 40 percent are of medium quality and about 20 percent are of low quality. Quality distribution may be better for smaller peals, while often only about 1percent of pearls above 9mm is of good quality. Lower quality pearls are used for pearl medicine.