Natural pearls are very rare these days due to over harvesting in the past. For them to be formed requires a unique set of circumstances. They are formed inside molluscs, moist commonly oysters and mussels. The process begins when an irritant gets inside the shell. This could be something as small as a tiny grain of sand or little stone. In order to protect the surface inside the mollusc a secretion known as nacre is secreted around the irritant. Layer upon layer of this lustrous substance builds up and so the pearl is formed. This rather amazingly can take up to seven or eight years. Although there is variation amongst the species as few as one in every thousand oysters or mussels might contain a pearl. And out of these only a few will be of the right quality and texture. In terms of quantity, around three tons of oysters might only produce 3 or 4 perfect pearls. The most valuable pearls are perfectly symmetrical, relatively large and produced naturally. They shine and shimmer and have an iridescence known as orient lustre. The main oyster beds lie in the Persian Gulf, along the coasts of India and Sri Lanka, and in the Red Sea. Chinese pearls come mainly from freshwater rivers and ponds, whereas Japanese pearls are found near the coast in salt water. Freshwater pearls also occur in the rivers of Scotland, Ireland, France, and Austria. The different locations and types of water where the molluscs are found produce local variations in colour, ranging from white, to those with a hint of colour, often pink, to brown or black.
Cultured pearls as the name suggests are cultivated by human intervention. Foreign material serving the same purpose as the irritant in natural pearls, is implanted inside the mollusc. It takes 2 - 4 years for the pearls to be created in saltwater and 2 - 7 years for freshwater pearls. Either way it's not a speedy process but perfection cannot be hurried. This method was first used in 1893. Saltwater pearls are created in a number of different colours including pink, blue, black, green and white. However to complete the perfect necklace matching colours, shades and pearl sizes can actually take years, which is why they are so expensive and highly sought after. The only way to distinguish natural pearls from cultured pearls is by the use of an x-ray. The coasts of Polynesia and Australia produce mainly cultured pearls.
Imitation pearls are man-made objects designed to look like real pearls. They can be made from a variety of materials including glass, plastic and even small pieces of mollusc shell and a number of methods are used. Coating beads with a pearlescent type substance helps to imitate the iridescence of nacre. However they can easily be identified as imitation as they lose their lustre very quickly. They are of no monetary value.
Although perfectly round pearls are the rarest and most valuable they come in eight basic shapes. These are round, semi-round, button, drop, pear, oval, baroque and circled. Round pearls are very rarely actually perfect spheres - if they are then they are a gem of the very highest quality. Pearls that remain inside the oyster or mussel for the longest time stand much more chance of developing an irregular shape.
The term "off-round" is used to describe pearls which are roundish to the eye but have a slightly oval or flattened shape. They can still have excellent qualities in terms of lustre or lack of blemish.
So far we have talked about the molluscs producing just one pearl. However the oyster or mussel can create up to a dozen or more pearls, depending on how many irritants seed within them. Some of these will develop as button pearls, so named because of their unusual shape, rounded on one side and flat on the other.
Pearls with an irregular shape are all known as baroque pearls and most natural pearls fall into this category. The most valuable of these are South Sea pearls and Tahitian. Baroque pearls make up a high percentage of all pearls harvested because of the length of time under cultivation.
A brief mention here about keishi or keshi pearls. Some people do not consider them to be natural pearls. They are formed out of something of an accident when the mollusc rejects the nucleus as it is forming. It grows into what can be described as a free form pearl. These pearls are sometimes called flower petal pearls and are particularly known for their shimmering lustre.
One of the most famous pearls in the world is called La Peregrina. Translated this means ‘the incomparable’. It was found in the Americas. The pear shaped white pearl is not only one of the most famous, largest and most expensive in the world, it also has a magnificent history. Upon discovery it weighed around 223 grains and has since been styled into brooches and pendants. This pearl has made its way through the hands of many people, starting with that of an African slave. His astonishing find won him his freedom by Don Pedro de Temez, the administrator of the Spanish Colony in Panama.
It is said to be the size of a pigeon's egg and it boasts many famous owners over the centuries, including Phillip II of Spain, Mary Tudor and even Napoleon III. In December 2011 the pearl sold for a record price of more than $11 million (£7.1m). La Peregrina was sold as part of Elizabeth Taylor's collection, which was being auctioned at Christie's in New York. This price surpassed all expectations after a mere four and a half minutes bidding. The private buyer from somewhere in Asia wished to remain anonymous.