FRESHWATER PEARL PRODUCTION:
Freshwater pearl production is surgical. The mollusk is opened a couple centimeters and an incision is made into the fleshy mantle of the mussel. The worker then inserts a piece of mantle from a donor mussel. This piece of mantle is square, and once it is inserted it is twisted to round off the edges. This gives the freshwater pearl it's off-round shape. Most freshwater mollusks are "seeded" with 12-16 pieces in either valve, for a total production of 24-32 pearls. After the nucleation process is done the mollusk is returned to the habitat and tended for 2-6 years.
China is the world leader in freshwater pearl production. They produced 1,500 tons of freshwater pearls in 2006. I think that makes them the clear leader no matter what. Someone has enough time to seed and harvest that many pearls should be named leader. The world's pearl trading hub is also the largest marketplace for freshwater pearls and is located in Hong Kong.
Today's freshwater pearl quality is much better than it has been in past decades. This is due in large part to the switch from Cockscomb pearl mussel to the Triangle shell in the '90s. The Cockscomb is responsible for the rice-crispy freshwater pearls of the '70s and '80s. Cultivators also went from inserting up to 25 grafts into each mussel to only inserting 12-16. This stressed the mussels less and resulted in better quality pearls.
Where fresh water pearls differ from saltwater - other than the cultivation differences - is that a fresh water pearl is pure nacre. There is no nucleus once the pearl is formed. That little piece of mantle inserted in the nucleation process is no longer present. Salt water pearls actually have very little nacre whereas freshwater pearls are solid. Because of this, freshwater pearls are very long lasting. They are also somewhat easier to cultivate than the seed-nucleated saltwater pearls.
The harvest of freshwater pearls is the final act of the mussel. The flesh and shell are discarded or used for another purpose. Oysters, anyone? After the pearls are harvested they are cleaned of debris and then polished. They are then sorted by size and quality. Depending on the farm or factory, the pearls may then be subject to other treatments such as bleaching and dyeing or "pinking," where they are soaked in a red dye to enhance the pink color.
Again, the cultivation of these pearls is surgical. The marine mollusk is opened a few centimeters and an incision is made into the gonad (the sexual organs) of the mollusk. Unlike the freshwater pearl, which is nucleated with a donor piece of mantle and then returned to the water, the marine mollusk is nucleated with a rather large bead and a piece of donor material behind it. The epithelial cells form a pearl pocket around the bead and nacre is secreted around it to form the pearl.
After the bead nucleation is done, the mollusk is allowed to recover. Because the nucleation process is more traumatic, there is a high fatality rate. Once the recovery period is over, the mollusk is returned to the habitat and tended for up to 6 years depending on the pearls being cultivated. Akoya pearls are cultivated from 8 months to 2 years, while South Sea or Tahitian pearls are cultivated from 2-6 years.
Akoya oysters can be nucleated with up to 5 beads, but the use of only 2 is the most common. The Akoya dies at harvest. South Sea and Tahitian mollusks can produce only 1 pearl at a time, but they do not die at harvest so they can be nucleated many times. A South Sea or Tahitian mollusk that has produced many high-quality pearls may be released back into the wild to contribute to the next generation.
Because of the larger size of the nucleus in saltwater pearls, there is significantly less nacre on them than the solid nacre freshwater pearl. Due to this, the nacre will wear down to the nucleus with wear. In x-ray, the nucleus is clearly visible in a saltwater pearl while there is no nucleus in a freshwater pearl.