Keshi pearls
Keshi pearls are small non-nucleated pearls typically formed as by-products of pearl cultivation. A Japanese word also meaning “poppy”, it is used in Japanese for all pearls that grew without a nucleus. Originally, keshi pearls referred to those pearls formed when a bead nucleus was rejected. More recently, keshi has been used to refer to second harvest pearls and even to freshwater non-nucleated pearls.
However the later usage referring to freshwater pearls is considered erroneous by many leading gem trade associations. Because they have no nucleus, keshi pearls are composed entirely of nacre.
Nacre known as mother of pearls
Nacre pronounced "NAY-kər", also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent.
Nacre is found in some ancient lineages of bivalve gastropod and cephalopod. The inner layer in the great majority of mollusk shells is porcellaneous, not nacreous, frequently resulting in a non-iridescent shine or less commonly in non-nacreous iridescence such as flame structure (e.g. conch pearl).
Pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Many other families of mollusk also have a nacreous inner shell layer, including marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.
Keshi pearl origins
All of the following can cause a keshi pearl to grow:
- An attack on a pearl-producing mollusc by a predator that bores through its shell... similar to a way in which wild natural pearls are formed, except that captive molluscs are more susceptible.
- Accidents causing injury to molluscs, for example driving shell fragments into mantle tissue.
- Cultivation mishaps, generally separation of the mantle tissue graft from an inserted nucleus... this causes the intended nucleated pearl to fail, and a smaller keshi pearl to grow instead.
- Deliberate non-nucleated cultivation, still the most common type in freshwater pearl farming.
- Keeping freshwater molluscs with pearl sacs alive after harvesting the (first round of) pearls.
Except to the extent of noting that extremely small pearls (<2mm) are not cultivated, since there is no incentive to do so because naturally occurring tiny pearls are relatively plentiful, it is usually not possible to determine which of these caused an individual keshi pearl to grow. Because most keshi pearls come from farms where they are commonly and deliberately cultivated, it is necessary to classify keshi as cultivated / cultured pearls. Any natural pearl (without nucleus) may be called a keshi pearl, but doing so would be rather meaningless without mentioning the species of mollusc in which the pearl grew, or at least its geographic provenance. Use of “keshi pearl” without provenance is confusing and should be avoided.
Origin of Name / Ambiguity
“Keshi” (occasionally misspelled Keishi, apparently a confusion with “Heishi beads”) was first used in Japan to describe pearls without nucleus. Akoya pearl cultivation, which began in the 1920s in Japan, provided numerous small, most often greyish pearls as a by-product. Traders from India, where natural pearls were harvested and processed during past centuries, needed no sales talk to be convinced that they could sell Japan Akoya keshi in their market and to visiting Arabs as natural pearls, because their close similarities.
Having access to Indian labor capable of sorting, drilling and stringing tiny pearls, arrangements were made to send Japanese keshi pearls to India (even during many years in which imports were not sanctioned); provide processing services at conditions without rival; and covertly retain pearls for sale in India under an allowance for pearls ruined in the course of processing.
Pearl importers in consumer countries, and the trade associations they constitute, have recommended limiting the use of the term keshi to ocean pearls, and banning its use for freshwater pearls. This is justified to some extent by the fact that ocean pearl keshi were known as a product for some years before their freshwater counterparts. Japanese language usage of keshi certainly includes freshwater pearls. It has always been a generic term, not a trademark, and its application to freshwater pearls by the Chinese is based on visual similarity that is quite close. Restrictions proposed would likely be futile, but would do nothing to resolve the ambiguity among various ocean pearl sources (Akoya, Southsea Kasumi, Tahitian) that can be eliminated by using keshi only in conjunction with mollusc name/species and/or provenance.
Chinese use of keshi for freshwater pearls is generally limited to those from a second (or subsequent) harvest. These differ considerably from the plump, full shapes of first-harvest freshwater pearls, which grow during a young mussel's growth period, when nacre production is at its peak. Older mussels produce nacre more slowly, and second-harvest freshwater pearls (if not nucleated) are generally flat and often thin, with concavities and texture mostly absent from first-harvest pearls. Curiously, the Chinese use keshi to differentiate between two distinct products, while Japanese usage, requiring only the absence of a nucleus, is equally applicable to both.
Source: Wiki