When talking about the size of a pearl, you must talk about the variety of pearl as well. For example, size of a Chinese Freshwater Pearl is very different from size of a South Sea Pearl. The Freshwater Pearl is cultured using mantle-tissue nucleation; the South Sea Pearl is cultured using bead-nucleation. Mantle-tissue nucleation adds virtually nothing to the size of the pearl. Bead-nucleation is used to define the size of the pearl -- the bigger the bead, the bigger the pearl.
In this article, I will use two bead-nucleated pearls to discuss the Size Value Factor, one of seven value factors to consider when purchasing pearls and pearl jewelry. Tahitian cultured pearls and South Sea cultured pearls are both cultured using bead-nucleation. In bead-nucleation, a bead made from a freshwater mussel shell is inserted into the oyster as part of the culturing process. Also common to these pearl culturing processes, only one pearl is grown at a time. If the oyster produces a healthy, marketable pearl, the oyster may be implanted again. The subsequent nucleus must be slightly larger -- the size of the pearl just removed. So, the second generation pearl is larger.
The oyster is returned to the waters for its growing period. As with the first generation, this is 18 months to 3 years depending on the farm, growing conditions and desired results.
Upon harvesting the second generation pearl, a third generation implantation may occur. This is rare. As the oyster ages, the quality of pearls it produces goes down. Luster is highest in the first generation.
Can you tell if you are buying a first generation pearl or a third generation pearl? No. You cannot tell the 'parentage' of the mollusk just by looking. If you are working closely with the farm, you may have this information. But even the farm is most interested in producing fine quality, lustrous smooth pearls.
This article focused on considerations regarding size of just two varieties pearls. The best rule of thumb? Buy the pearls with the highest luster and the smoothest surface for the best investment value. Buy the pearls that appeal to your heart for the most pleasure.