Keshi Pearls: Properties, Benefits & Meanings

What are Keshi Pearls?

Keshi is a Japanese word also meaning “poppy” (ケシ, 芥子); it is used in Japanese for all pearls that grow without a nucleus. Originally, Keshi pearls referred to pearls that were formed when the nucleus of a bead was rejected during production.

Recently, Keshi pearls have been used to refer to second-harvest pearls and even freshwater non-nucleated ones.

Many leading gem trade associations consider using “Keshi pearl” to refer to freshwater pearls because Keshi pearls mostly have no nucleus and are composed entirely of nacre.

A pearl is a complex, shining object that forms within an oyster or another type of mollusk.

Like the mollusk shell, which is produced by layers of calcium carbonate depositing in crystalline form, pearls are made from calcite or aragonite.

They are tiny, non-nucleated pearls that form as byproducts during the cultivation of other pearl types.

Origins

The following are all causes of Keshi pearls:

• Similar to how wild natural pearls are formed, an attack on a pearl sac by a predator that bores through its shell creates Keshi pearls, except that captive mollusks are more susceptible.
• Injuries to mollusks, such as driving shell fragments into mantle tissue.
• Cultivation mishaps usually occur when a mantle tissue graft separates from an inserted nucleus which causes the intended nucleated pearl to fail, creating smaller Keshi pearls.
• Most Keshi pearl farming is done with a type of cultivation called deliberate non-nucleation.
• Keeping freshwater mollusks alive after harvesting the pearls attached to their shells.

Although it should be noted that miniature pearls (<2mm) are not cultivated since there is no financial incentive to do so because naturally occurring tiny pearls are relatively plentiful. It usually isn’t possible to determine which of these caused an individual Keshi pearl to grow.

Terminology and History

“Keshi” originated in Japan as a name for pearls without nuclei. The cultivation of Akoya pearls, which began in Japan in the 1920s, produced tiny greyish pearls as a byproduct. This was mostly practiced in the South Sea. Champagne pearls are also farmed from this location.

Traders coming from India, where natural pearls were harvested and processed during past centuries, needed no sales to talk to convince them that they could sell Japanese Akoya Keshi in their market. Because of the similarities between these cultured and natural pearls, the traders sold them to visiting Arabs without hesitance.

The availability of a skilled labor force from India enabled the arrangement to be made for Indian workers to sort, drill and string tiny pearls known as Keshi.

Where are They found?

Keshi pearls are obtained from the following countries:

• China
• Japan

Japanese Vs. Chinese Pearls

Pearl importers in consumer countries, and the trade associations, have recommended that only ocean pearls be called Keshi—not freshwater or cultured pearls. This is explained by the fact that ocean pearl Keshi was already a known product before freshwater versions became available.

In the Japanese language, the usage of Keshi certainly includes freshwater pearls. However, it has always been a generic term, not reserved for freshwater pearls, and its application by the Chinese market is based on visual similarity.

Chinese use of the word Keshi for freshwater pearls is generally limited to those from the second harvest. Second-harvest pearls differ considerably from the plump, full shapes of first-harvest freshwater pearls. This is because during a young mussel’s growth period—when nacre production is at its peak—second harvest mollusks produce smaller beads.

The Chinese use the word Keshi to differentiate between two different products, while the Japanese usage—requiring that a nucleus be absent from an otherwise intact cell—is equally applicable to both.

Nature vs. nurture controversy

It is impossible to know if an individual Keshi pearl grew serendipitously or was inserted into the mantle tissue artificially makes them all classified as cultivated/cultured pearls.

It is possible to give any information about the type of Keshi pearls by examining supply and demand. However, all types of mollusks used for pearl cultivation, both ocean and freshwater species, naturally contain tiny pearls called seed pearls (less than 2 mm), so devising ways to cultivate small pearls has never been in demand.

The labor-intensive process of making Akoya pearls resulted in many tiny “byproducts” called Keshi, which had little or no value. On the other hand, Southsea pearls are farmed in more giant mollusks and can be pretty valuable.

In pre-1985 Japan, freshwater cultivators commonly used bits of active mantle tissue left over from in-body bead nucleation by slipping a few Keshi into the body.

Because Keshi farms in China are discarded rather than used, the market for them is too small to make it worth expending even a tiny fraction of the mussels’ strength on producing freshwater Keshi. Freshwater Keshi pearls from China are cultivated but in an indirect way. 

What Are Their Physical Properties?

They have the following physical properties:

Mineral Group	Pearls
Formula	CaCO3
Chemical name	Calcium Carbonate
Color	White, Pink
Hardness (Mohs scale)	2.5 – 4.5
Refractive Index	1.52 – 1.66
Specific Gravity	2.60 – 2.85
Transparency	Translucent, Opaque

Typical Appearance

Keshi pearls are made of solid nacre and have high luster. Most of the colors typical of cultivated mollusks are represented among them, but in the case of Akoya pearls, they often contain more gray than bead-nucleated ones.

Their lustrous shine is a result of light being reflected, refracted, and diffracted off the translucent layers within their shells. Therefore, the more layers in a pearl—and the thinner they are—the more refined its luster is.

Cultured pearls come in various colors— White, pink, silver-, cream-, golden-colored and green– among the most common. However, when viewed through their top layer, the most valuable pearls have a luminous luster reminiscent of metal surfaces like platinum or silver.

Because they don’t have a bead nucleus, Keshi Pearls are solid nacre. Keshi occurs in a wide variety of unique shapes. In contrast to saltwater Pearls, baroque shapes predominate in Keshi varieties—that is, the strand will consist mainly of irregularly shaped pearls rather than round ones. On average, their sizes can run from six to ten millimeters or 0.2 inches.