The pearl grafting procedure consists of introducing a nucleus and a graft into the gonad (the sexual gland) of an oyster. The nuclei used for this purpose are beads made from the shells of fresh-water bivalves (Pleurobema cordatum or Fusconaia ebenus) which are imported not only from Japan but also from the Mississipi and the Yang-Tsê Kiang in China. The graft is a piece of  the mantle of a healthy oyster.

• The procedure :

- The preparatory stage :

Mature oysters aged 2 to 3 years, at least 12 cm in length, are taken from the rearing station, detached and stored in crates either at the grafting workshops, which are located near the rearing stations, or by the coast. Farm houses on stilts, such as the one shown in the following photograph, provide the most suitable conditions for transferring the oysters from one place to another.

• The grafting equipment

The nucleus:  various sizes of nucleus are used, depending on the size of the oyster into which it is to be implanted. Since the nucleus is the substrate on which the layers of nacre will be deposited, its structure and surface characteristics must resemble those of a pearl and be as smooth as possible so as to maximise the chances of obtaining a completely round pearl. The various layers of calcium carbonate which form the lustrous nacre covering a pearl are actually only microscopically thick. They will therefore mirror any imperfections present on the surface of the nucleus. Improving the quality of the nuclei therefore also improves the quality of the pearls. This is why, based on the scientific evidence obtained in 1990, special attention is always paid nowadays to the polishing of the nuclei by the world's cultured pearl experts in Japan, the United States and China.

The equipment: to prevent the risk of introducing pathogenic agents which may be harmful to  Pinctada margaritifera, it is expressly forbidden to import previously used equipment into the Territory. Some special derogations are possible, however, when the equipment is duly sterilised upon entering the Territory.

• The grafters' know-how 

The first grafted pearls (which were hemispherical in shape) date back to 18th Century China. Two Japanese inventors, Mr. Mise and Mr. Nishikawa, were really responsible for discovering how to graft and produce pearls, however, since they obtained the first round cultured pearls in 1905. It was only in 1916 that another Japanese inventor, Mr. Mikimoto, took out the first patent rights to the production of the white Japanese "Akoya" pearl.

Since the Japanese kept their know-how secret in this way, they were the world's only grafters of Pinctada margaritifera pearls up to the 1980's. Even today, they are still obtaining record nuclear retention rates (as checked 45 days after the grafting procedure) of about 65 % on average, and they sometimes score rates as high as 90 % in the most successful production cycles.

Owing to the fast development of this sector in Polynesia which occurred in the 80's and 90's,  a shortage of qualified oyster grafters soon arose. The average salary offered to those with the requisite know-how increased considerably, often reaching as much as 50 000 FF a month. Since not many of the pearl farmers were able to afford salary costs on this scale, those involved in this sector of activity decided to join up and form companies or associations with a view to diversifying their sources of recruitment.

Two solutions were adopted :

On the one hand, some expert Chinese grafters were engaged, since their standard of living and their salary requirements were lower than those of the local oyster grafters. In addition, these people's high standard of workmanship meant that they were able to achieve higher graft success rates. In response to the pearl producers' demands, some Economic Interest Groups (EIGs), including the "Tahiti Pearl Producers", recruited twelve Chinese oyster grafters  in July 1998. The Chairman of the latter group, Mr. Franck Tehaamatai, explained that these employees had been offered renewable one-year contracts with a government-owned company. The contributions paid by the members of the EIG covered the cost of the Chinese workers' travel expenses, as well as their health insurance, food and accommodation. Although they had all acquired 4 to 8 years' professional experience, the Chinese oyster grafters had to undergo vocational training for one month in order to adapt to the difference in the size of the oysters, since the "Akoya" variety are much smaller. The chairman summed up his opinion of the new recruits in the following terms: 

"They are inexpensive, hard-working, submissive and can remain seated for eight hours at a time" Since they were paid three times less than the local oyster grafters and ten times less than the Japanese specialists, these Chinese workers certainly constituted a remarkably cheap labour force. 

The second alternative was proposed jointly by the Territorial Department responsible for the Sea and Aquaculture  and the Ministry of the Sea, which set up a training college (Centre des Métiers de la Nacre et de la Perliculture – CMNP) in Rangiroa in 1991.
The aim of this college was to enable its students to acquire the knowledge and techniques involved in mother-of-pearl and pearl production. The students are mainly young Polynesians wanting to take up this delicate profession, which requires both specialised knowledge and some experience. After the college had been open for two years, the first local "Paumotu" oyster grafter to graduate in 1998 was Mr. Petero Tupana. Mr. Tupana is now self-employed. He is producing round pearls and achieving graft success rates of 70 to 80 %. His professional history shows that it takes a great deal of patience and perseverance to succeed, and M. Tupana has pointed out that this is precisely why there are so few qualified oyster grafters available locally. 

• The formation of the pearls :
  Before they are ready to be harvested, pearls take a long time to form in successive layers around the epithelial cells implanted in the host oysters along with the artificial nucleus.
  The following diagrams, which are reproduced from the review "Te Reko Parau" published by the Department of Marine Resources, are cross-sections showing how a pearl is gradually formed.

• The pearl products : 
  

  The development of a pearl requires many months of patience and investment on the part of the producer before it is of any value. These natural gems are all unique, since they differ in their size, shape and colour (photographie). When the pearls are ready to be marketed, all these characteristics are assessed and classified.

  The by-products:

  Pearls which are not perfectly round and regular are often termed "ringed" or "baroque" pearls (i.e., they have no symmetry axis). 

  If the nucleus has been rejected, the graft sometimes produces its own pearl concretion, yielding a "keshi" , which is a kind of baroque residue in which the layers of pearl have accumulated unequally around the graft (photographie).

A mabe or semi-cultured pearl is a crude pearl which has been re-worked after the following stages have taken place:

. Half of an artificial nucleus is cemented to the internal surface of a Pinctada margaritifera shell, under the mantle, and is then coated with the successive layers of nacre secreted by the host oyster.

. The pearl is then manufactured as follows: the "mabe" is split open, the half-nucleus is removed, and the cavity it contains is filled with resin and covered with a piece of polished mother-of-pearl (photographie).Mother-of-pearl is formed in layers in exactly the same way as oyster shells. 

Once the pearls have been harvested, the host oysters are no longer of any use. This is why the above operation is always carried out using oysters which will no longer be used for grafting purposes.

The other by-product which is used a great deal in the local arts and crafts is the Pinctada margaritifera shell itself. The shells are cleaned,  polished, and sometimes engraved, and help to diversify the range of pearl products marketed on the Territory.