As diamonds have the 4 C's of CARAT, CUT, COLOUR & CLARITY, we have our 5 main criteria for judging the value of a pearl. They are SHAPE, SIZE, LUSTRE, COLOUR and SURFACE.
 

Shape

Round is the rarest shape and therefore the most expensive, followed by long drops, then ovals, buttons and finally circles. Shape is actually a matter of taste or preference depending on what the pearl is being used for i.e. ring, pendant, earrings or necklace.

Size

The size of the pearl has a very significant impact on its price. No matter what type of pearl, the bigger sizes are rarer and therefore command a premium price.

Lustre

The lustre of a pearl refers to the pearl's brightness and its ability to reflect light. Generally the better the lustre is then the thicker the pearl nacre. Lustre is the most important feature of a pearl as a brighter lustre attracts the eyes and makes people notice your pearls.

Colour

Colour depends very much on personal tastes although certain colours do command premium prices. Silver-pink and white-pink are the most prized colours in the White South Sea Pearls followed by white, silver, silver/blue, cream and yellow. The deep gold colours are very rare and command a high price. The most prized colours in the Tahitian Pearls are the peacock-green and peacock red followed by the aubergine or red/black colours.

Surface

A clean surface is important and the cleaner the pearl the more expensive it becomes. If the surface marks are very small or can be cleverly hidden in the jewellery setting then it is possible to have a very beautiful piece of pearl jewellery at a reasonable price.

Most importantly you should only buy pearls which you like and which look good on you. Different pearls can suit different people.