Birth of an Oyster:
21 days after oyster fertilization, larvae will search for a place where they can stay attached like corals or any other materials.
To catch these larvae, pearl farmers use collecting stations made with a framework of plastic shades and hung on a rope where they become young oyster (spat).
Between 21 and 24 months, collecting stations are removed from the sea for oyster cleaning in order to keep them in a healthy condition to produce quality pearls.
Young Oyster sizes are about 5cm and 10cm depending on the time stored in water. Oysters are washed and marine growths are removed from the oyster to avoid parasites.
Preparing oysters for grafting.
There are three main techniques for preparing the oyster for grafting.
1. Nakasai: Oysters are drilled and affixed to ropes using a technique called Nakasai from its inventor or “chaplet on ropes”. Most say in French, CTN (Chapelet Technique Nakasai ou nacre).
2. Lantern basket: Pyramid shape of plastic basket that hold five to 10 oysters per basket. These lantern baskets (up to four) are hung on a rope.
3. Pocket or kangaroo baskets are a rectangular shape of plastic basket that can hold 14 to 48 oysters.
They are generally placed into a sea nursery near the farm to let them grow for three months to one year. When they reach nine to 11 cm (adult size) they can be raised from the sea for grafting.
Grafting or seeding is a delicate process that needs high technical skills. A small piece of mantle tissue called “greffon” in French is cut from the donor oyster and implanted in the oyster pocket that will develop the Tahitian pearl. Selecting the donor oyster is crucial; this will affect the final colour of pearl. The nucleus is also inserted carefully into the oyster pocket to make sure that it touches the mantle tissue “greffon”. Once the grafting is done, oysters are returned to the sea.
The nucleus (bead) is made from mussel shells from the Mississippi river in the USA. Some have experimented using their own oyster shells with success, saving import fees and protecting the Mississippi mussel from mass fishing. If the mantle tissue is not correctly inserted, the nucleus can be rejected from the oyster, giving birth to a keishi (poppy seed pearls) rather than a pearl. After 30 days the entire nucleus is covered by “aragonite”, a secretion of calcium carbonate layer similar to the mother-of-pearl.
Eighteen to 24 months after the grafting, it’s time to harvest. Oysters (Pinctada Margaritifera) are washed and pearls are extracted from the mother-of-pearl. Pearls are polished and ready for sorting in different categories.