Shape: Every pearl is unique. The most precious pearls – and also the rarest – are round. However, there are many other shapes, including droplet, bouton, baroque, flat, and oval pearls.
Lustre: This is the most important factor in determining the quality of a pearl. Lustre is the result both of how light is reflected off the pearl’s surface, and how it is refracted by the aragonite crystal layers that make up the nacre. Generally speaking, the thicker the nacre layer, the better the lustre.
Size: The diameter of a cultured pearl also affects its value: the larger it is, the more the pearl is worth.
Surface quality: The value of a pearl also depends on its surface. Any blemishes such as hollows, bumps or other unevenness will lower the value. However, cultivated pearls can sometimes attract a good price even with this sort of blemish, provided they also have a thick nacre layer, deep lustre and distinctive colouring.