The three types of pearls include natural, cultured and artificial. The method for identifying natural pearls from artificial is fairly simple, but differentiating between cultured and natural pearls is more complicated because they are formed in the same manner. Performing a number of tests helps verify if the pearl is of natural origin. If there is still doubt and the pearl in question is of value, it is best to have the pearl tested by a certified professional as none of the tests that can be performed at home are definitive.
Rub the pearl gently against a front tooth. The smoother it feels the more likely it is cultured or fake. A natural pearl feels rougher because the outer layer has irregularities and a grainy texture.
Examine the interior of the drill hole with a magnifying lens. A series of growth lines strongly indicates a natural pearl. There is usually a dark line between the nucleus and the nacre that forms the outer layers of the pearl. In a cultured pearl, this line will be closer to the outside edge and more visible because they do not usually develop as long as a natural pearl. However, this line may have been removed with bleach. The drill hole of a natural pearl is rarely less than .04mm while a cultured pearl's is .06mm, according to Gemstone Buzz.
Hold the pearl in front of a strong light source. A dark round smudge at the centre is indicative of a natural pearl. A cultured pearl with thin skin exhibits a series of parallel stripes indicating growth layers around a bead or mother or pearl centre and are usually not found in natural pearls. The thin brown line between the nucleus and nacre may be visible near the outer edge in a cultured pearl.
Feel the pearl. A natural pearl feels cool to the touch.
Examine the pearl closely under natural sunlight. If there are slight variations in size, shape, colour and shine it is more likely to be a natural pearl.
View the pearl under a black light. Cultured pearls usually fluoresce a uniform milky white while natural pearls appear tan or yellowish with variations in the intensity of the colour.
Roll pearls on a strand on a white surface with a strong light focused on them. Cultured pearls with thin skins seem brighter and darker as they roll because the nucleus shows through the nacre layered around it. This makes the pearls look like they are winking in the light. This only works with cultured pearls that have thin skins.