A keshi pearl is a non-nucleated pearl produced as a by-product of cultured pearl farming, formed when a mollusc rejects or expels its implanted bead while retaining the donor mantle tissue, or when extra mantle tissue gives rise to additional pearls in the gonad. The result is a pearl composed almost entirely of nacre, without the bead nucleus that characterises standard cultured pearls. The name derives from the Japanese word for poppy seed, a reference to the small size of the earliest examples.

Formation

In standard bead-and-tissue cultured pearl production, a small bead, typically a piece of shell from a freshwater mussel, is implanted in the mollusc together with a graft of mantle tissue from a donor oyster. The mantle tissue forms a pearl sac that secretes nacre over the bead. In some cases the bead is rejected before nacre deposition begins, while the pearl sac continues to grow and to produce nacre around itself; the result is an all-nacre pearl. In other cases additional fragments of mantle tissue produce satellite pearls alongside the principal nucleated pearl. Either route gives a keshi.

Forms and colours

Keshi pearls are typically baroque in shape, ranging from elongated and twisted forms to flatter discs and irregular ovals. Sizes vary from a few millimetres up to ten or more, with larger keshi being uncommon. They occur across the species and farming regions used in pearl culture, including Akoya keshi from Japan, Tahitian keshi from Pinctada margaritifera, and South Sea keshi from Pinctada maxima. Colours follow the host species: silver and grey for Akoya, the full Tahitian palette of dark grey through peacock and aubergine for Tahitian, and white through gold for South Sea.

Trade status and disclosure

The trade has historically treated keshi as a kind of natural pearl because they are all-nacre and unintentionally formed. CIBJO and the GIA, however, classify them as cultured pearls of a particular kind, on the grounds that the parent mollusc was implanted by human action and the pearl sac itself originates from a graft. The distinction matters for valuation: keshi command less than equivalent natural pearls and more than standard cultured pearls of the same size and quality. Sellers should disclose them as keshi cultured pearls rather than as natural pearls.

Use in jewellery

Keshi pearls have a strong following among jewellers who value the irregular forms and the all-nacre lustre, which is generally higher than that of nucleated pearls of comparable size because the entire body is nacreous. They are particularly favoured in contemporary art jewellery and in pieces by makers such as Hemmerle, Suzanne Belperron's later interpreters, and a range of Japanese and Italian designers. Strands of matched keshi are uncommon and command a premium.

Identification

Distinguishing keshi from natural pearls and from beadless freshwater cultured pearls requires laboratory examination. X-radiography reveals the absence of a bead nucleus, while internal growth structures and microradiography help differentiate keshi formed from a residual pearl sac from genuinely natural pearls. Buyers paying natural-pearl prices should always request laboratory documentation.