A general term used by pearl traders for pearls that grow accidentally in the soft tissue or the adductor muscle of cultured pearl-bearing mollusks. Chien Lin, president of Inter World Trading, says that the term "keshi" started out referring to a type of natural pearl in Japan, but over time, the term became much more broadly used internationally. Having grown up in the pearl industry in
Kobe, Japan, Lin had the opportunity to meet many old-generation pearl traders. They told him the term "keshi" was initially used to refer to natural seed pearls found when harvesting wild Akoya oysters. Since the tiny natural pearls resembled poppy seeds, they called them keshi, which means "poppy" in Japanese. Lin has verified this usage of the term with a specialist at the Mikimoto Pearl Museum in Japan.

After the Japanese started culturing Akoya pearls, the term "keshi" was also used for the by-products of Akoya cultivation that did not contain a bead nucleus. These form from nacre secretion around microorganisms or shell particles that enter the pearl during pearl nucleation. The nacre may also be secreted around detached fragments of the mantle inserted with the pearl nuclei (mantle is a membranous tissue that secretes nacre and lines the inner shell surface of mollusks. It's inserted with the pearl bead nucleus to help stimulate nacre formation). Mantle tissue keshi have also been called "saibo (tissue) keshi," but most traders just call them keshi. Akoya keshi pearls can range from small "seed-sized" to skinny pearls as long as 14 mm.

The term became more confusing when freshwater pearls and South Sea pearls from the silver- and black-lipped oysters entered the market. Keshi from South Sea pearl oysters are generally much larger in size than Akoya pearls because of the size of the mother of pearl and speed of the nacre formation. Even though South Sea keshi seldom look like poppy seeds or tiny pearls, the term "keshi" is used to refer to these by-products of South Sea oysters. There is a large range of sizes for South Sea keshi-from small seed-sized to the size of a baby's fist.

To add another element of confusion to the term "keshi," Chinese reborn freshwater pearls (Zai Sheng Zhu in Mandarin) came into the picture. A reborn pearl is grown out of the pearl sack of a mussel in which a pearl was carefully removed at harvest so as to not kill the mussel. Another pearl will grow out of a pearl sack, after healing, without another implantation of a mantle or tissue. (This tissue is originally necessary to initiate the virgin grafting to stimulate pearl nacre formation). Some people call these "born again" pearls.

Freshwater reborn pearls are not new to the market. This category of pearls had been available from Biwa Lake pearl farms in Japan when Biwa pearls were still in production. (Actual pearl cultivation in Biwa Lake faded out in the late 1980's, leaving very few farmers still cultivating on a small scale). At that time, Biwa pearl traders did not use the term "keshi" for reborn pearls; they simply called them"Biwa pearls," the general term for freshwater pearls produced at Biwa Lake.

Some traders refer to Chinese reborn pearls as "natural pearls" or "Biwa pearls," but both terms are wrongfully used. Reborn pearls are not natural pearls because they are cultivated, and "Biwa pearl" is a general term for freshwater pearls out of Biwa Lake in  Japan. Most of the Chinese freshwater pearl cultivation techniques came from Japanese pearl farmers, so too the South Sea pearl culti­vation techniques of the black- and silver/gold-lipped pearl oysters.

Chien Lin prefers to refer to these reborn pearls as "keshi-type cultured freshwater pearls" because the nature of the reborn pearls is different from that of other
keshi pearls. Reborn pearls are intentionally created while keshi pearls are created by accident.

Japanese Akoya keshi are becoming more and more difficult to find because of recent decreases in Japanese Akoya pearl production, but some other types of keshi are becoming more available due to the increase in overall production of freshwater pearls and black, white and yellow South Sea pearls. Akoya keshi are sent for processing to countries with low labor costs because the majority of Akoya keshi are very small or thin and thus have smaller-than-usual holes that must be drilled by hand without using any power tools.

In summary the term "keshi" has been used to refer to five different types of pearls. They are:

1.   Natural seed pearls. The term "keshi" was used for these pearls before cultured pearls ever existed.

2.   Pearls that form as by-products of the Japanese Akoya pearl oyster culturing process from nacre secretion around microorganisms or shell particles that enter the pearl during pearl nucleation. The nacre may also be secreted around detached fragments of mantle tissue inserted with the pearl nuclei. The Akoya oyster has only one grafting and one harvest of cultured pearls and keshi.
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