Freshwater pearls born from mussels in lakes or rivers, typically originate in the regions of south/southeastern China and Japan. Amongst all pearls, freshwater pearls are the most versatile in regards to color, shape and size.
Unlike saltwater pearls, which are cultivated using beads as their nucleus, freshwater pearls are cultivated with small pieces of tissue. And, as they are left to develop longer than any other type of pearl a lustrous orb of nearly 100% nacre is produced. The resulting high quality and affordability make freshwater pearls a mainstay in the fine jewelry market.
The earliest known experiments in Freshwater Pearl cultivation can be traced back as early as the 1300s in China to Yu Shun Yang, who is credited with inventing the method for culturing blister pearls by lifting the mantle and placing a shaped mould between the mantle and the shell.
The first successful batch of freshwater pearls on a commercial basis, known as Biwa pearls, was produced in Japan's Lake Biwa in 1925. The initial harvests, while very lustrous, were small and off-shaped but with time and experimentation, rapid progress was made in the ability to consistently produce standard shapes and sizes. It was also discovered that unlike a saltwater oyster, a bead nucleus is unnecessary for the cultivation of a freshwater pearl, but what only needs is the insertion of a piece of mantle tissue secreting nacre from a donor mussel, resulting in breeding pearls with pure nacre composition. Unfortunately, in the early 1990′s, the production of Biwa pearls almost came to a halt due to a vast death of Biwa mussels.
About 30 years ago China successfully adopted the freshwater pearl cultivation technique to produce high quality pearls in large quantities. These first Chinese pearls were white and rice-shaped.
Freshwater pearl cultivation today
Today, China is producing the majority of Freshwater Pearls in the world. The cultivation techniques of Freshwater Pearls in China have been developed and improved for over 30 years, the quality has been significantly improved and the pearl size was being enlarged steadily. Due to the absence of bead nucleus to help guide pearl growth, Freshwater Pearls composed of solid nacre are difficult to formed as round shape, but nowadays, this difficulty has been overcome, and perfect round Freshwater Pearls over 10.0mm or even 12.0mm are quite commonly seen at the high-end freshwater pearl market.
The most productive host for high quality freshwater pearls is a triangle shell species (Hyriopsis Cumingi). As Freshwater pearls need pure nacre to be deposited layer by layer, the harvesting period is longer than saltwater pearls, sometimes can be as long as seven years. During the cultivation period, constant care and attention is required to assure that the mussels thrive and produce the best possible pearl crop. And with a unique cultivating technique which only uses mantle tissues rather than shell bead nucleus, freshwater pearls are composed of almost 100% nacre.
What actually makes freshwater pearls more affordable is not lack of quality, but rather the higher productivity of the host mussels used to produce them. One freshwater mussel can produce up to 40 pearls compared to one or two pearls produced in each saltwater oyster.
A Varied Array of Freshwater Pearl Colors
While practical purposes oblige retailers to simplify color description, as in the illustration above, in actual fact, freshwater pearls cover the widest range of natural colors in the pearl family, with dozens of subtle variations. The color of a freshwater pearl is determined both by the mussel itself and its living environment.
In the current freshwater pearl market, the most popularly seen colors are white, lavender, peach/pink and black. While white pearls are the most traditional and popular, the unique qualities of natural lavender and pink are rapidly becoming the favorites of more and more pearl lovers. Other rare natural colors, such as those with metallic hues can increase the value of a freshwater pearl. Freshwater mussels do not produce black pearls, deep dying techniques have been developed which permanently change the nacre color to a black sheen and black freshwater pearls.
In addition to the main color of the body, due to varied compositions of pure nacre, a pearl can also have overtones. Overtones are enhanced by different light sources and background colors. Like the optical effects of sunlight on the rainbow, a blue overtone can be intensified by a florescent light, while a regular bulb light can enhance the color of yellow and red. Natural sunlight can reveal overtones of rose, blue and green, and the presence of overtones is precisely one of the ways a real pearl can be distinguished from an imitation (which have no overtones).
Freshwater Pearl Shapes
It is much easier to produce perfectly round pearls with the use of beads in the nucleation process, as is done with saltwater pearls. Freshwater pearls, however, are nucleated with tiny pieces of mussel tissue, and although this results in a composition of almost pure nacre, rendering pearls that are closest in nature to natural pearls, producing round pearls is a much greater challenge. In fact, only about two percent of initially harvested freshwater pearls are round or near round in shape. Happily, one freshwater mussel can breed a great many more pearls than saltwater species, and this higher productivity offsets the imbalance.
While the roundness of a freshwater pearl will definitely increase its quality and value, a careful screening process is required to distinguish pearls of highest quality (see Pearl Industrial Processes).
Freshwater Pearl Size
As freshwater pearls are almost pure nacre in composition, as opposed to saltwater pearls which contain beads at their center, they will hardly ever be able to compete in size with saltwater pearls. The size of freshwater pearls is normally within the range of 5-10mm with above 10mm considered to be rare and more valuable, while South Sea pearls are commonly 12mm in size and even larger.