A Comprehensive Guide to Saltwater Cultured Pearl Varieties
There are several kinds of Marine (or Saltwater) Cultured Pearls:
1) Mabe or Half-Pearl:
This kind of pearl is formed when one (or more) nucleus (usually a hemispherical shaped piece of plastic or shell) is attached between the oyster's shell and its mantle (this is the organ that secretes the mother-of-pearl shell).
The oyster's reaction to this "intruder" is to coat it up with millions of nacre (the substance that makes up a pearl) layers to "protect" itself. After a culture period of 6 to 18 months the oyster is harvested and the mabe are found attached to the oyster's shell, so they are cut from it with the help of lapidary equipment, the nucleus is removed and the remaining piece, a hollow dome of nacre, is filled with epoxy resin and a "backing" made of mother-of-pearl shell is put on the underside. Thus a fully processed mabe is ready to set into jewelry.
Mabe are easier to obtain -when compared to loose cultured pearls- thus their price is usually lower than most cultured pearls, but they can also reach very big sizes and can make a very good fashion statement when used in conjunction with other pearl jewelry. Mabe can come in a surprising variety of unique and unusual shapes, thus making them very appropriate for jewelry designers that want to produce unique creations.
2) Loose, Round or Cultured pearls:
These are the ones most people instantly identify with the word "Pearl". Some experts prefer the term "loose pearl" or "cultured pearl" over the term "round pearl", simply because many cultured pearls do not come out totally round, but in many other shapes.
Loose pearls are produced trough the use of the Mise-Nishikawa grafting technique and the Arizmendi-Nava-McLaurin technique. There three kinds of loose pearls: the bead-nucleated (marine), the tissue-nucleated (freshwater) and the keshi pearls.
Marine/saltwater pearls are always bead-nucleated (except for Keshi). This includes every single cultured pearl available today: Akoya, South Seas and Sea of Cortez, be them from China, Japan, or any other pearl producing country.
The main reason for this is that, without the use of a round shell nucleus bead, it is virtually impossible to obtain a fully round pearl. Even so, fully round pearls only appear in 5 to 25% of a pearl harvest. Of course, we are considering the pearl harvest as being a "good quality harvest", and by this we mean that the pearls were allowed to grow for a minimum of 18 months (nacre thickness of at least 0.9 mm).
3) Keshi pearls:
The word "Keshi" in Japanese means "poppy seed". This is the common term used to identify a pearl that is produced by the oyster trough the use of the grafting technique, but in this case, the oyster got rid of the nucleus, by expelling it, but the mantle tissue survived and eventually formed a baroque shaped pearl with no nucleus inside of it. The nucleus acts as a "shape guider" for the pearl sac, and with nothing to "guide its actions" the oyster does as best as it can.
The main difference between a Keshi and a (nucleated) cultured pearl is the absence of a nucleus (bead). The difference between a cultured and a natural pearl is basically the same. So, are a keshi and natural pearls the same thing? No. A keshi is a cultured pearl. Within its core you will find a sizable quantity of decaying organic matter (remains from the oyster's gonad), whereas a natural pearl has the decaying body of an intruder (and usually it is much smaller).
Keshi come in different size, shapes and coloration, and are specially sought after by those that seek a refreshing new look in their jewelry designs.
Summing up, there are many kinds of cultured pearls out there in the world markets...some are excellent, some are good some are not that good, so be careful when selecting a pearl. Sometimes the price tag says it all, sometimes it does not...remember to use the distinguishing attributes of a pearl as your allies: luster, orient/overtones, nacre thickness and color.
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