Pearls are produced by molluscs and have the same composition as the shell that encloses them.
Natural pearls are very rare and are usually irregular in appearance; this means that today they are almost exclusively the prerogative of the flea and antiques market.
In nature, the beads are formed as the self-defence mechanism of the shellfish in respect of grains of sand or small parasites that penetrate to its interior. The deposition of the layers of nacre around the foreign element has in fact the aim of isolating it.
Cultured pearls, just like natural pearls, are produced by molluscs, their formation, however, is not linked to a random event, but to human intervention.
PEARLS CULTIVATED WITH NUCLEUS
In Japanese cultivated pearls, called Akoya, a spherical pearl necklace, the nucleus around which the oyster builds the pearl, is inserted into the same bivalve. To get good quality products takes about twenty-four months.
The Akoya hardly exceed 9 mm in diameter and are grown in the sea.
Tahitian pearls, deposited in a mollusc named Pinctada Margaritifera, are cultivated in a similar length of time and manner as those in Australia, but have very particular shades of colour, ranging from light grey to purple-black.
Tahiti's pearls, deposited by a mollusc called Pinctada Margaritifera, have very similar times and ways of cultivation to Australia, but they have very distinct shades of color, ranging from light gray to purple-black.
These are pearls that originate from very large molluscs that live in the great Asian rivers. The cultivation method is completely different from the one seen so far in that between forty and fifty pieces of epithelial tissue of other molluscs are inserted into the large river bivalves, around which the nacre layers are deposited. It is a technique that ensures pearls without nucleus, composed entirely from precious biomineralisation, with shorter cultivation times and large-scale production: each oyster can produce up to fifty pearls.
The high quality achieved in recent years, both in terms of shape and diameter and brightness, means that today it is really hard to tell the difference between sea pearls with a nucleus and river pearls without a nucleus, without the support of a well-equipped gemological laboratory.