They say that you can distinguish a natural pear from a cultivated pearl with your teeth. Honest. Apparently, so the experts say, you can tell one from the other because of the pearl’s surface: if it’s gritty, it’s a natural or cultivated pearl, worked on by a clam or oyster pearl; if it’s slippery, it’s likely a plastic, fake pearl.

Natural pearls are made when an irritant finds its way into inside the shell of an oyster or clam. In response, these bivalves quarantine the intruder, whether a grain of sand or an invading worm, by coating it with a calcium carbonate substance known as nacre (pronounced nay'ker). Over time, layer after layer of nacre produces a subtly luminous, iridescent pearl. These naturally occurring pearls were the ones predominantly used in jewelry making up until the 1920s.

During the Jazz Age, pearl "farmers" made cultured pearls by implanting the clam or oyster with a "seed." Pearl makers over the years have experimented with various seeds, including a glass marble, a plastic bead, or a rounded piece of pigtoe clam shell, which produces the most desirable of all cultured pearls. It’s a delicate operation because you have to open the shell, but you can’t kill the clam or oyster. By manipulating a clam's environment and other factors, cultured-pearl makers can alter the size, shape, color, and clarity of a pearl. Black water, for example, begets black pearls, very popular today.

There’s a new crop of marketable cultured pearls every year or two, whereas natural pearls take between eight and ten years to form. Fresh and saltwater farmers all over the world mass-produce cultured pearls, which now practically monopolize the pearl market because they sell for about one tenth the price of the far rarer natural pearl. (A consumer can pay as little as $25 for a 50-pearl strand.)

It’s almost impossible for even highly trained professionals to tell the difference between cultivated and natural pearls. Experts use an x-ray to probe the pearl’s drill hole to look for onion-like layers. A natural pearl will have them, a cultured pearl’s large beaded centre will not.

A less high-tech way to examine pearls requires a flashlight and a 10x loupe to inspect the thread hole. This low-tech examination can be carried out at home.

If you want to purchase pearls remember: the rounder the pearl, the more it costs. So if you're willing to put up with, or even prefer, the vagaries of nature, buy irregularly shaped pearls with blemishes, called "baroque" pearls. They were popular in the early Renaissance and are used today to make unusual figural pins. White and pink pearls are more expensive than creamier ones, and a walnut-sized pearl will cost you more than tapioca-sized ones.

If you want to preserve your pearls: remember that one of the biggest threats to a cultured pearl is an overzealous cleaner. Pearls, like all jewelry, get dirty after repeated wearing.

Unfortunately, misguided pearl owners often scrub them with an abrasive. If you use an abrasive, you’ll strip away the natural surface of the pearl and it’s far easier to erode the pearl down to nothing than you think. Simple and gentle is best, so clean your pearls with mild soap and warm water.