Freshwater pearls are typically tissue-nucleated (though recently there have been almost round to baroque bead nucleated pearls available. These seem to have a softer glow and more subtle colours than the other bead nucleated freshwater pearls... squares, sticks etc.) meaning they are composed entirely of nacre; the fragment of mantle tissue is absorbed as the mollusk coats it, or is drilled out; the result is a pearl made of solid nacre. Some specially shaped pearls , such as square or coin seem to have a piece of shell inserted to achieve the shape, though I haven't been able to find any information on this. (with great difficulty- involving a brick and a hammer- I broke a stick pearl in half to have a look, though I've also seen reborn or second harvest- stick pearls which I expect would be all nacre). Amongst the various types of pearls available, freshwater pearls are prized for their durability, their diversity and warmth, and above all, their affordability.
Freshwater pearls are available in a myriad of colors, shapes, and sizes. In addition to the traditional white body color, these pearls come in a rainbow of natural colors as brilliant as lavender, peach, mauve, some greys, pink, and every shade in between. Their varied shapes include potato-shaped and stick pearls, toothpick, rice-shaped and button pearls, coin-shaped, square, rectangular, heart and drop pearls, off-round and round pearls. My particular favourites are Drusy and keshi (Drusy is the term for a bumpy, pimply surface , also found in other gemstones). Only 1 percent of pearls are formed like this.Very rare and very different. Glorious keshi pearls, small, roundish, rosebud shaped natural pearls, or petals used to be formed accidentally in the soft tissue of the mollusc during the cultivation process. These days, in Chinese freshwater pearls anyway, I hear they are formed as a second harvest. After pearls are removed from the mussel, the pearl sac is left intact and the mussel put back into the water for another 2-6 years; nacre continues to be deposited in the pear sac, resulting in what are now generally called 'keshi' freshwater pearls, second harvest or reborn freshwater pearls. *(Thank you for that information Jeremy). Perfectly round freshwater pearls are pretty rare. Keep in mind that even the roundest freshwater pearls are almost never perfectly spherical, although they may appear so to the naked eye. Their sizes range from tiny seed pearls measuring 1 or 2mm in diameter to 15mm and larger.
Freshwater pearls are produced by Hyriopsis cumingi (triangle shell) and Hyriopsis schlegeli (Biwa shell) commercially in China, and other bivalve mollusks that live in lakes, riverbeds, and creek bottoms in Japan (Biwa pearls and Lake Kasumigaura pearls), as well the United States (Mississippi River Basin). Although several areas of the world are home to pearl-producing mussels, the global freshwater market is overwhelmingly dominated by Chinese pearl farms, which account for nearly all of the freshwater pearls sold today. At these farms, each mussel is surgically implanted with 24 to 32 tiny pieces of mantle tissue, a process known as nucleation Once they have been nucleated, the mussels protect their flesh from the irritants by secreting nacre , the calcium-carbonate compound known more commonly as mother-of-pearl. This is the same beautiful, iridescent substance that lines the inside of mollusk shells and coats the surface of pearls. Over the course of 2 to 7 years, the mussels deposit layer upon layer of nacre around the growing gems. By the time the pearls are harvested, each mussel has produced more than two dozen pearls densely clustered on the inside of its mantle tissue. This mass-production can sometimes compromise the quality of the resulting pearls, and very high quality freshwater pearls are quite rare. During the harvest, the millions of pearls are sorted carefully and matched for size, shape, color, and quality. I buy them on temporary strands from China, before I string them onto silk; sometimes I just sort the pearls by size, but sometimes I also sort by the overtone colour ( lavender pearls, for example, may have a bronze, green, gold , blue or rose orient). For myself,I prefer them unsorted, as the different overtones are more apparent.
Freshwater pearls are dazzling with their rich, bright lustre, and their unique charm will last you a lifetime. They are a pleasure to work with and I am constantly amazed at the glorious colours when I wear them in bright daylight, particularly.When your new pearl purchase arrives, please take time to look at them in different lights. Bright overcast days are perfect.