Coin pearls exhibit some of the hardest lustre seen in pearls, simply because a flatter area of nacre reflects light more intensely, like a mirror, rather than scattering it like a convex or irregular shape. However, the luster is rarely equally intense on both sides of the pearl. Cutting flat shell pieces in various shapes has given us lozenge, drop, square, rectangular, heart, star, plum blossom, crescent moon and gourd shapes, to name a few. More intricate shapes such as animals or pagodas are easily rendered unrecognizable by too much nacre. Coin pearls made using Chinese antimony coins of small denomination have also been seen occasionally, as have pearls with wax or resin nuclei, but we avoid these products because drilling holes in them for stringing or setting may be problematic. A new type of pearls we call lightweight coins has been on the market since 2008. Most sellers claim they are non-nucleated, and indeed they are thinner than baroque coin pearls previously seen. Unlike coins, many are also slightly curved, but some reveal a partial outline of a circular nucleus. For more details, please read lightweight coin pearls. Flat shell nuclei placed in pearl sacs grafted in the mantle produce a coin pearl that is somewhat flatter than button pearls that can be cultivated with no nucleus. Coin pearls are popular in necklaces and for setting in pieces that benefit from flat shape, typically earrings and bracelets. They are generally equally flat on both sides. We carry mostly coins with thick nacre, which tend to be irregular and baroque and not to conform faithfully to the nucleus shape.
Chinese fw pearls without nucleus often have a button or lentil shape, typically domed on one side and somewhat flattened (sometimes with loss of lustre) on the other. This is thought to be due to running out of space between the mussel's body and its shell. Coin pearls are flatter than button pearls, whose thickness is more likely to increase with diameter. Chinese dealers call nucleated coin pearls "buttons" (Cantonese: lam kam) and non-nucleated button pearls "buns" (Cantonese: min bao).
Coin pearls have been made in China since the mid-1980's, gradually overcoming an initial tendency to have holes in the nacre. The product was familiar, as it had been previously produced in Japan. Apparently it became popular as a cultivation method, and a lot of producers achieved success within a short time. The result was a glut that depressed prices to where nobody could cover costs. Many coin cultivators appear to have shifted to other products or quit pearling, and fewer coins seem to be available.