The most valuable Tahitian & South Sea Pearls are round. Of course, nature rarely makes anything truly perfect, but “round” pearls should virtually perfectly round to the naked eye; no more than a few degrees off round that would have to be measured by calipers. Next would be the “off-round” or “semi-round”–these are basically round, but look a bit squashed in one axis that is pretty easy to detect. They are usually drilled through the shortest axis, so the lack of roundness is less noticeable when strung. “Drops” are pear shaped with one end more pointed–they can be long or short drops. “Baroque” includes drops & most everything else–usually lumpy potato shapes and ovals.
“Mabe” pearls are formed when the nucleus becomes stuck to the inside of the shell & a half-round pearl with a relatively flat back is formed. Mabes are used in earrings, pendants and flat mounted bracelets. “Keshi” pearl have no nucleus & are free-form, usually in flake or twig shapes. South Sea/Tahitian keshis are pretty rare. “Buttons” have flat backs are are generally more symmetrical than mabes.
Conversely, keshis are very commonly grown in freshwater pearls in a dizzying array of shapes, including twigs, sticks, flat, cross and disc. All the other shapes are available in fresh water as well.
Pearl values are determined by the size, color, shape, surface and rarity. Like most gemstones, the fewer flaws, the more valuable. Consider that the longer a pearl is growing (i.e. the bigger it gets), the longer it has been in the oyster and the more likely it will have blemishes. Therefore, like most gemstones, a flaw that would be a serious issue in a small specimen becomes more tolerable in a larger one.
There are pearls in every price range. A pretty string of off shaped, small freshwater pearls could be $100-200 or less, while a string of large, round Tahitian would command $5,000-10,000 or more depending on quality and color.
Next week in the last of my pearl posts, I’ll talk about how to evaluate pearls when you are shopping.