There are five key factors that determine the quality of a pearl:
‘Lustre’ refers to the shine of a pearl. A pearl with a good lustre is often described as looking as though it is ‘glowing from within’, whereas a pearl with poor lustre will look somewhat flat and dull. When examining pearls, try and look at them in a natural light to see how well they reflect the light: the sharper the reflection, the better the lustre.
Just like with diamonds, the value of the pearl is not wholly determined by the size but rather their rarity, but as a general rule the larger the pearl the higher the price tends to be.
There are three main shapes of pearls: round, drop and baroque. Perfectly round pearls are the most desirable and therefore more expensive.