Tissue-nucleated Freshwater Cultured Pearls
Tissue-nucleated freshwater pearls are the closest in composition to a natural pearl since they are made primarily of concentric layers of 100% solid crystalline nacre. Conchiolin, an organic protein produced by the mollusk, functions as a base coat and is generally the first layer deposited by the pearl sac. It acts as a form of glue or adhesive and surrounds the bead or tissue nucleus. Alternating layers of conchiolin and crystalline nacre will continue to form causing subsequent nacre layers that are produced to bind together. The nacre thickness and quality of a pearl not only determines its unique beauty but also, it's life. Nacre thickness is directly related to the period of time that pearl farmers allow the implanted nucleus (bead/mantle tissue) to remain in the mollusk.
Cultivation periods for cultured pearls can be from 6 months to several years. The period for freshwater pearls is generally shorter than that of saltwater pearls. However, the shorter the period the thinner the nacre. Buyers can reasonably assume that pearls with shorter periods of cultivation will not last as long as those with longer cultivation periods (the thin layer of nacre will wear-away and their beauty will rapidly vanish). When purchasing pearls, inspect around the drilled holes near the knots for signs of chipping, which may be an indication of thin nacre or the use of a dull drilling bit. Pearl farmers are always confronted with choosing between long cultivation periods, escalating production cost, and the risk or danger of naturally occurring climate changes and disasters. Longer cultivation periods also allow for factors that affect the pearl's shape and surface qualities. Imperfections can occur that directly relate to the pearl's value.