The most important factors taken into consideration when valuing cultured pearls are lustre, colour, shape, surface and size.

Lustre

The most important indication of a pearl's quality is lustre. The lustre of a pearl refers to the glowing appearance of its surface, and is judged by it brilliance and ability to reflect light. A pearl with a high lustre will be very shiny and show reflections like a mirror while a pearl with poor lustre will appear very milky or chalky.

Lustre is determined by the quality of a pearl's nacre-its transparency, smoothness and overall thickness. Factors affecting the quality of the nacre include the cultivation place, the health of the mother oyster, the length of time spent in the oyster, pollution and the type of oyster used. Only strong layers of nacre can produce deep lustre.

It is better not to compromise on lustre as this feature cannot be hidden or enhanced by its jewellery mount.

Colour

Pearls present a whole palette of colours to choose from. Light coloured pearls are produced in shades of white, pink, silver, gold and blue, while dark coloured pearls range from peacock green and aubergine purple to all the shades of grey.

Above all, a pearl's colour is a question of personal taste. Although some shades are especially rare or popular and therefore highly valued, such as rosy white, silvery white and pale gold, the colour of a pearl is certainly not an indication of its quality.

Shape

The shape of a pearl plays a major role in determining its value. Pearls can be divided into four basic groups of shape. These are in order of value:

Throughout history, the round pearl has been considered the most valuable and popular shape. However, most of the world's most famous and valuable pearls are often not symmetrical in shape, and that is because the other grading factors are also important.

Shape is a good category to compromise on if you need to cut down on price. Actually, baroque and circled pearls can make for very interesting jewellery pieces.

Surface

The fewer the spots or blemishes a pearl has, the higher its value. But again flaws can also be positive features. They may serve as identifying marks that a pearl is yours and not somebody else's, and help prove that it is real and not imitation.

Flaws can also lower the price of a pearl without necessarily affecting its overall beauty.

Size

The size of a pearl is expressed in terms of its diameter, which is measured in millimetres. Size has a significant impact on price. One millimetre's difference has been known to raise a price by between 100 and 200 per cent.