Freshwater pearls are pearls which have formed in the shells of freshwater mollusks, commonly mussels. Initially, freshwater pearls were not as highly prized as saltwater pearls, but advances in culturing techniques for pearls have led to a higher demand for freshwater pearls. The majority of cultured freshwater pearls come from China, where techniques have led to cultured pearls which are almost indistinguishable from natural ones.
A pearl forms when an irritant is introduced into the shell of a mollusk. In nature, this may take the form of sand, a chunk of rock, or some other organic material. Cultured pearls are made by inserting an irritant into the shell, commonly a piece of shell from another mollusk. The mollusk forms a layer of protective material called nacre over the foreign material so that it will no longer irritate the animal. The resulting ball of luminous nacre is known as a pearl.
Like saltwater pearls, freshwater pearls can come in a range of colors. The color of the pearl can also be further enhanced with bleaching and dyeing, allowing producers to make pearls in a range of colors available. Perfectly round freshwater pearls are extremely rare, and therefore highly prized. Most freshwater pearls are baroque pearls, meaning that they are irregularly shaped. Commonly, these pearls are simply more ovoid in shape, or take the form of tear drops. Flattened wing pearls are also not uncommon.
Many jewelers work with freshwater pearls. When the pearls are irregularly shaped, the jewelry is commonly designed to highlight this, rather than trying to conceal it. Distributors usually provide freshwater pearls on long strings, and the pearls should be removed from the string and washed before use. Most freshwater pearls are double strung when they are used in jewelry, to prevent breakage and a resulting loss of pearls. They are also used with metals such as gold and silver, and are often combined with stones in flattering cuts and colors.
The colors of freshwater pearls are determined by the water the mollusks live in, the placement of the pearl in the shell, and the species of the animal. Shape is not so controllable, as a pearl is a natural formation. After pearls are collected, they are graded by shape and Orient, the luster of the nacre. Round pearls with luminous nacre are the most expensive, because they are the rarest.