The lustre of a pearl is what makes each pearl unique. Because of this, the price of the pearl is often valued on how lustrous it is. Pearls are measured according to their lustre, which is the quality and amount of light that is reflected from the surface layers of the pearl. If a pearl has a high lustre, it will reflect light and images brilliantly. Saltwater pearls often have much more lustre than freshwater pearls, which can often appear dull, white and chalky due to the lack of lustre.
The amount of lustre a pearl has depends how the nacre layers have developed whilst the pearl is being formed. This also has an effect on the length of time the pearl takes to develop inside the mollusc. Pearls that have a high lustre have a higher concentration of nacre and are much more expensive that pearls with less nacre and therefore less lustre. The keshi pearl, also known as the poppyseed pearl is 100% nacre and is considered to be the most lustrous of all pearl types. Despite this, the keshi pearl is often less expensive than other pearls that have been cultured.