The trump card of the Polynesian economy, the poe rava (black pearl) is the result of natural phenomena and complex human intervention. The main centres of production are on the Tuamotus and in the Gambier Archipelago. Manihi,Takapoto, Takaroa, Arutua,Makemo and Mangareva are the best-known. Their lagoons, studded with pearl farms standing on piles, look like lakeside towns. The size of the operations varies from one or two people to more than 80 people on the industrial sites. The cause of this activity is an oyster,Pinctada margaritifera, found in abundance in Polynesian lagoons. The shells of these bivalves were used in ancient times to make ceremonial jewellery, fish hooks and lures, and were once much sought-after by the European button industry. The over-exploitation of natural beds and the decline of the button industry sounded the death knell in the 1960s, and the culture of oysters for pearl production took over, initially on Manihi. The formation of a pearl results from the accidental or artificial introduction of a foreign body inside the oyster. In response to this intrusion, the epithelial cells of the mantle (the secretory organ) produce material to isolate the foreign body. In this way, the nucleus is gradually covered in nacre (mother-of-pearl). If the foreign body (eg a grain of sand or coral) is introduced by natural means, the result ia an extremely rare natural pearl, known as a fine pearl. The pearl farmer must reproduce this natural mechanism. Firstly, the oysters are methodically reared. At certain times of the year, they release sexual substances that are fertilised in the water. After swimming around for several weeks, the young oysters (seed oysters) attach themselves to the coral. The pearl farmer catches the seed oysters in artificial collectors sunk in the lagoon and then attaches them to underwater rearing lines. The first stage consists of sacrificing a perfectly healthy mature oyster, known as the donor oyster. A fragment of its mantle is removed and divided into about 50 minute particies, called grafs. The second stage is the grafting proper, which takes just a few seconds. The recipient oyster is fixed to a support and then held open with forceps. Using a scapel, the grafter firstly incises the back of the gonad (reproductive organ) and inserts the graft. A perfectly spherical bead (the nucleus), about 6mm in diameter, is introduced into the gonad so that it is in contact with the graft. The graft cells develop around the nucleus to form the pearl sack which, once closed, secretes the nacreous material. The grafted oysters are placed inside keepnets (metal baskets) and lowered back into the lagoon. They are then regularly inspected and cleaned. Layer upon layer, the mother-of-pearl thickens around the nucleus at the rate of 1mm a year. Eighteen months later, the first harvest is gathered. A second nucleus may be implanted to obtain a second, larger (15 to 20mm) pearl 15 months later. Grafting entails risks inherent to all surgical operations: of 100 grafted oysters, 25 to 30 do not survive the shock of the operation and another 25 to 30 reject the nucleus. When the time comes to harvest them, only five of the remaining 40 (just 2%) will have produced perfect pearls. When a second graft is performed, the success rate increases to just under 10%. Untill recently, the only grafters were Japanese. They were virtual superstars who had to be retained at great expense, but they are gradually being replaced by Polynesians who have allegedly discovered the 'secret' of the technique. A centre for the pearl-shell and pearl-culture professions has been established on Rangiroa and provides traning for future pearl farmers. Nonetheless, the act of grafting is still partially veiled in mystery. The pearls are mainly used for rings and pendants. Several factors determine their value: the diameter (from 8.5 to 18mm); shape (whether it's round, ie perfectly spherical; ringed, ie with visible rings; baroque, ie asymmetrical;pear-shaped); quality (absence of flaws or marks) and color. 'Black pearl' is in fact an inaccurate term. The pearls produced by Pinctada margaritifera range in colour from pearly white to black, and include deep purple, champagne and gray. The orient (the pearl's iridescent reflection) and lustre (mirror effect) also enter into the equation. Jewellers generally classify pearls by using two letters followed by a figure; a pearl classed as RB 12 is perfectly round (R), has a few pits or surface flaws, a correct orient (B) and measures 12mm in diameter. Less well known, keshi and mabe are two other products of pearl culture. Keshi is pure mother-of-pearl a pearl without a nucleus. In some cases the nucleus is rejected but the secreting graft continues to produce mother-of-pearl. The resultant pearls vary from 2 to 8mm in diameter and are often baroque in shape; they are not discovered until harvesting and are used to make earrings or braclets. Mabe, by contrast, is the result of deliberate manipulation. The technician sticks a plastic mould on the inner surface of the shell. The mould is gradually covered in layers of mother-of-pearl. After a few months, the mother-of-pearl is cut off with a diamond disk and the mould is removed. The result is a pure, hollow mabe,which is filled with epoxey resin before a small mother-of-pearl plate is welded on to form the base. Mabe is highly valued in the jewellery trade for making pendants, brooches, earrings and cufflinks. Reproduced with permission from *Tahiti & French Polynesia, Edition 5*,(c) 2000 Lonely Planet Publications. www.lonelyplanet.com
