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. 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. Read further for more detail.