While looking at black pearls, the first thought to consider is their wide variety of shapes (round to circle), size (8mm-12mm), and colours (a rainbow palette of blue, green, rose, gold, silver, white, and more). In fact, black pearls are rarely black and receive their name not from their colour, but from the species of oyster that produces them, the black-lipped oyster. While there are several elements to pearl quality at the end of the day, always select a pearl according to your own personal desire and taste regarding shape, size, and colour. Pearl prices are still a function of the following five elements:
Shape: Round is the most sought after and is the most difficult to produce. The closer the pearl is to round, the higher the price. However, many other shapes have their charm as well, so always purchase a pearl that is most attractive to your individual taste. The shapes in order of value are Round - perfect sphere. Semi-baroque - button, oval, drop, and pearl shapes showing an axis of symmetry. Baroque - asymmetrical or irregular shapes. Circles - distinct rings prominently encircle the pearl's surface. Keshi - small cultured pearls that have no nucleus and are usually irregular in shape. Maybe - half pearls are grown on the oyster's interior surface.
Size: This is measured at the smallest diameter of the pearl, which usually ranges from 8mm - 12mm. Pearls rarely exceed 12mm and very exceptionally 15mm-18mm or more. As the size of the pearl increases, so does the price.
Lustre: The lustre of a pearl refers to the appearance of its surface and is judged by its brilliance and ability to reflect light. This can produce a mirror-like effect which can display orient of surface iridescence.
Surface: The surface quality is judged by the position and number of blemishes such as dents, scratches and stains, which all reduce the value of the pearl.
Colour: Black pearls present a whole palette of colours. The most prized include peacock green, aubergine purple, marine blue or any other rare colours. Generally speaking, darker colours are more valuable than light. However, one should always purchase a pearl colour that each individual finds most attractive.