Regardless of the type of pearl, many factors are evaluated for its beauty and value:
- Lustre and orient
- Nacre thickness and quality
- Surface perfection
Lustre and Orient
Lustre is the brightness that results from the rays of light travelling through the numerous layers of nacre and being reflected back from within the pearl. Pearls are valued for their high lustre (their sheen or soft glow); the higher the mirror-like finish the more desirable, as opposed to flat lustres.
Nacre thickness and quality
Lustre and nacre quality are closely related; nacre thickness and its quality have the greatest impact on the beauty of the pearl. The thicker the nacre the longer the life of the pearl; a less durable thin nacre means a shorter life. However, the quality of the nacre is equally important, because of how the light travels through the layers. It’s the combination of these factors that is crucial.
A smooth and clean surface is more desirable than a low blemished surface. Like coloured stones most pearls are rarely perfect. Some might show abrasions that look like surface scratches, or a flattened section, or an irregular ridge that looks like a crease or wrinkle. Numerous or severe ‘flaws’ can affect the pearl’s durability, lowering its value.
There are three shape categories:
The more perfectly spherical, the more valuable and the more popular (perhaps thanks to cultured pearls) but many depart from this shape and fashion, taste or trends also play a part in their desirability. Pear or drop shaped pearls are also highly prized. Highly irregular shaped pearls are called baroque pearls.
Pearl colour can have three components:
- Body colour is the pearl’s dominant overall colour
- Overtone is one or more translucent colours that lie over a pearl’s body colour
- Orient is a shimmer of iridescent rainbow colours on, or just below, a pearl’s surface
All pearls display body colour, but only some show overtone, orient or both.
Natural and cultured pearls occur in a broad range of hues and have a wide range of tone from light to dark. Pearl colours tend to be muted, with a soft, subtle quality. Broadly, body colours can be white, pink, yellow, grey, bronze, green, mauve and black. In addition, the orient may show delicate tints of pink, yellow, green or blue.
The value of certain pearl colours is all about the law of supply and demand. If supplies of high-quality pearls in a preferred colour are low, their prices can rise enormously. Other factors, like fashion trends and cultural traditions, can influence colour preferences. Or maybe a personal or regional preference – pink pearls are popular in America, cream and gold in the middle East and South America, while In Europe and the UK it’s all about classic cream or white.
Natural pearls are sold by weight, today normally carat weight. Cultured pearl prices and desirability increase with size, measured in millimetres. When other value factors are equal, larger pearls are rarer and more valuable than smaller pearls of the same type.
For pearl strands and multi-pearl pieces, how well the pearls match (or mix) affects their value. Jewellery designers sometimes deliberately mix colours, shapes and sizes for unique effects, but for most pearl strands, earrings or other multiple-pearl jewellery, the pearls should match in all the quality factors.