Lightweight coin pearls are an innovation that reached the market in 2008. They are somewhat thicker than non-nucleated second harvest pearls, aka Chinese freshwater keshi, but otherwise resemble them in overall shape and surface texture. Sizes reaching over one inch (25.6mm) across, rare among non-nucleated second-harvest fresheater pearls, are now readily available. Many have slight curvature, but an excess of thinness and curvature that made many non-nucleated second harvest pearls (a shape sometimes called "corn flake") awkward to string and set is largely eliminated. A close look at the shape of many (but by no means all) of these new pearls suggests the presence of a thin and flexible flat nucleus. Just as frequently seen in thickly-coated and therefore baroque-shaped coin pearls, a partial circumference of the flat nucleus cut in circular shape is frequently discernible in relief. Destructive investigation of such pearls revealed the presence of a flexible nucleus made of plastic sheeting. However, second harvest non-nucleated (aka Cfw keshi) pearls from sacs previously containing coin pearls closely resemble lightweight coin pearls in every way except this.
We were convinced that a new cultivation method involving nucleation is in use; however vendors insist that these are simply bigger and better non-nucleated second harvest pearls, widely known as China freshwater keshi. For our best explanation of how some of the goods we are currently selling were made, please read the next section for more detail. Freshwater pearls are grouped into strings and hanks, and into loose pearl lots based on similarity of look and value. There is usually no incentive to strictly separate pearls belonging to different types, such as with and without nuclei. Strands made of baroque coin, flame and non-nucleated second harvest pearls (aka keshi) mixed together have been common for some years, as many originate from the same production stream. We may categorize some or most pearls in a group as belonging to a given type, but there are some pearls in most groups that could belong to other types. In such cases we must point out that our categorization is of the majority and may not apply to every pearl in the group. Efforts to acheive ever bigger pearls are active on two fronts in the freshwater sector. Bead nucleation holds out the best hope of producing rounder, higher value pearls. In China, in-body nucleation is currently performed by only a small minority of cultivators, but they have produced roundish semi-baroque pearls exceeding 16mm diameter while Japan has not, at least since 1985.
Most bead-nucleated Chinese pearls are of the "flame" type, made by re-nucleating pearl sacs previously grafted in the mantle. Flame pearls rarely maintain the nucleus shape; with thick coating they tend to be very baroque. The massive size record for bead nucleated pearls is probably held by extremely baroque flame pearls with enormous overgrowth in several directions.
Read more about Flame pearls.
The alternative is increasing the area and thickness of basically flat pearls. Stick-shaped freshwater pearls created by inserting long strips of mantle tissue folded in two are a type known as "Biwa" among Chinese vendors. When pairs and groups of sticks are grafted close together, they may produce large second harvest pearls because the pearl sacs, cut open to remove the pearls, tend to merge into a larger single sac. Such superlarge sacs can produce very large coin pearls, and plastic sheet may be used in the same way. However, the size and thickness of many lightweight coin pearls exceed what could grow in the second harvest. An interesting variation resembling a leaf with a big stem occurs when a stick and a lightweight coin are grafted close together so that they will grow joined. We can probably expect more artistic innovations as techniques are refined.
More massive than pearls produced in a second harvest, lightweight coin pearls are cultivated by inserting pieces of plastic sheeting together with large grafts of mantle tissue in a first operation. The broken pearl in the photo grew around a textured bit of plastic like imitation leather. The size and weight of many examples indicate that they have been in mussels for several years. The downside of very large size pearls in the mantle is that the chances of the pearl being joined to the shell are increased. A majority of the largest pearls produced with flexible nuclei, and as a second harvest following them, stick to the shell. Pearls' value is sharply reduced by gaps in their surface nacre wherever they have to be cut from the shell, and jewelry makers strive to hide such cuts. Unlike shell nuclei (bead and coin) thin bits of plastic contribute little to the weight of the pearl. This might be a reason that so many vendors call these lightweight-coin pearls non-nucleated. The average price per weight of coin pearls is lower than that of non-nucleated second-harvest pearls, partly because coin pearl nuclei represent a considerable part of the weight of the pearl produced, and a pearl without nucleus is all nacre. Since the relationship between the weight of cheaper inserted material and of the pearls harvested is probably more similar to non-nucleated pearls than coin pearls, the wish to classify the product with the former group is at least understandable. Many cultivators of coin pearls appear to have switched to producing lightweight coins because the market for coin pearls had fallen below production costs during the recent glut. Nucleation is generally done using shell, and no shell is used in lightweight coins. Another factor that helps deter disclosure about nucleation with bits of plastic is that the use of materials other than shell as nuclei is frowned upon in general. The reason is that the usability of the pearls may be adversely affected. Materials with significantly different expansion coefficients may produce pearls that will spontaneously crack as a result of temperature changes, and difficulties in drilling holes are common. We have not done much drilling of lightweight coin pearls, but the problems appear to be less severe than those we have experienced with other non-shell nucleus materials such as antimony coins or wax beads. There tend to be irregular spaces and sharp edges along the drill holes, however, that may be an obstacle to speedy restringing in some cases. A similar technique using celluloid flat nuclei was experimentally used in Japan to make "dragon" pearls, which are flat and very large, often with several non-nucleated pearls adhered to one face. A problem encountered with celluloid nuclei is that drilling into them may generate enough heat to cause discoloration of the pearl. Given a strong prejudice throughout the pearl establishment against nucleation with any material other than shell, examples from Japan are very scarce. Like them or not, lightweight coin pearls are a significant part of China freshwater pearl production, apparently replacing much of the slower and therefore higher-cost production of non-nucleated second-harvest pearls of large sizes. Pacific Pearls offers lightweight coin pearls and mixed strands incorporating them in a variety of shapes and sizes. We are eager to disclose what we have learned about all the types of pearls we sell, because this allows customers to make informed choices, and to avoid making inaccurate claims.