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Keshi pearls are small non-nucleated pearls typically formed as by-products of pearl cultivation. A Japanese word also meaning “poppy” (ケシ, 芥子), 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.〔(【引用サイトリンク】title=Keshi pearls is a term used to describe several varieties of pearls. | Kojima Pearl Company )〕 Because they have no nucleus, keshi pearls are composed entirely of nacre. ==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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Keshi pearls」の詳細全文を読む スポンサード リンク
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