Genuine Tahitian pearls are valued for their characteristic dark color, which is often described as black but in reality ranges from silver to graphite, often with subtle blue, purple, pink or green tones. The color comes from the black lips of a giant Tahitian oyster. Jewelry with real Tahitian pearls is highly valued and often copied with imitation pearls made from glass, plastic or shell-plated beads, so how do you know if your pearl is genuine? Asking your boyfriend if the necklace he just gave you is made of real pearls would really spoil his romantic gesture. There are several ways to find out that don't involve offending your BF.
Examine the pearls closely and -- if your piece of jewelry has more than one pearl -- compare the pearls with each other. Because Tahitian pearls are a natural substance, they are rarely perfectly round, flawless or identical to each other. If every pearl on a necklace is absolutely identical in shape, size and color, this is a good indication that they are imitation pearls.
Test the texture of the pearl by lightly scratching it along the biting edge of your front teeth. If it feels perfectly smooth, it is probably a fake pearl. A real pearl has a slightly gritty surface texture. If you have two pearls, you can also assess their surface texture by rubbing them against each other.
Examine the pearl under a magnifying glass, the more powerful the better. If the surface appears grainy, it is probably an imitation pearl. A genuine pearl will appear to have a scaly surface marked with wavy, maze-like lines.
Measure the diameter of the pearl with a ruler. Genuine Tahitian pearls generally range from 9-to-12 mm in diameter. The largest can reach 15 mm, but these are very rare and very expensive. If your pearl is any bigger than 15 mm across and you know it wasn't super expensive, it is more than likely a faux pearl.
Examine the hole drilled through the pearl under a magnifying glass. You should see a distinct line between the iridescent nacre (the mother-of-pearl, or outer layer of the pearl) and its core. A genuine Tahitian pearl usually has a nacre about 1 mm thick or more. If the nacre is considerably thinner than this, it is probably fake.