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Pearl Jewellery

When choosing pearls it is useful to learn how pearls are formed, about the different types of pearls available, and how to select good quality pearls.

A pearl is formed when a small object or irritant becomes embedded in the tissue of an oyster or mollusc. The mollusc secretes nacre, a combination of crystalline and organic substances, around this irritant to protect itself. As the nacre builds up in layers, it eventually forms a pearl, with the irritant as the centre. Natural pearls are those formed in this way by chance – they are therefore fairly rare. Cultured pearls are made by deliberately inserting a foreign object into the tissue of an oyster or mollusc. In this way, pearl farmers can induce the creation of a pearl and have control over the way the pearl grows.

In selecting pearls, quality is of the utmost concern. Fine, well-strung and perfectly matched pearls with thick nacre layers will maintain their luminescence, durability and lustre for years. Cultured pearls of high quality are increasingly rare today. It is therefore important that you deal with a jeweller you trust. Unlike diamonds, cultured pearls are not evaluated by an industry-wide grading system. However, some merchants have developed their own grading scales for comparative purposes. Because we believe quality is so crucial in a cultured pearl, Astley Clarke goes to great lengths to ensure that all cultured pearls found on our website are carefully chosen for their quality, shape, size and lustre.

Discoveries made in the 19th and early 20thC by Japanese researchers, particularly Kokichi Mikimoto, have been instrumental in the process of culturing pearls. Mikimoto discovered a specific technique for creating a round pearl within the tissue of an oyster – before his innovations, although pearls could be cultured, they tended to be hemispherical mabes (hemispherical pearls grown against the inside of the mollusc or oyster shell). This revolutionized the pearl industry, because suddenly pearl farmers were able to reliably cultivate large quantities of high-quality pearls.

Whereas natural pearls, as well as being hard to find, come in a huge variety of shapes, sizes and qualities, cultured pearls are specially produced to be round and primarily flawless. The whole process is monitored throughout, to ensure the optimum survival and health of the mollusc and thus the most perfect possible pearl. It also allows tens of thousands of pearls to be cultured, so that the price of pearls has dropped enough to make them easily and widely available, although large and perfectly formed pearls are still relatively expensive, because of the considerable amount of work and culturing time that has gone into them. Cultured ‘seawater' pearls (although they are hardly ever referred to as such) also remain more expensive than freshwater pearls because the movement of seawater and the living organisms it contains makes culturing them over several years more difficult than in freshwater. There are several types of pearls known for their distinct beauty, including South Sea Cultured Pearls , Tahitian Pearls , and Keshi Pearls .

South Sea Cultured Pearls


South Sea pearls are among the largest cultured pearls in the world. The South Seas are between the northern coast of Australia and the southern coast of China. The large oyster, the pinctada maxima, is found here. This oyster can grow up to 12 inches in diameter and can therefore be nucleated with particularly large beads. South Sea pearls are usually monitored and grown for 2 years before they are harvested. This explains the size of these pearls.

An average South Sea pearl measures 13mm, and most harvests produce a range of sizes between 9mm and 20mm. The nacre of South Sea pearls is unusually thick, and because it is particularly rapidly deposited from warm waters, has a uniquely satiny lustre. As well as white, South Sea pearls can also be found in a variety of colours that are unusual in other types, such as silver and gold.


Tahitian Pearls


Black Tahitian pearls are produced by the black-lipped oyster in the islands of French Polynesia. Tahitian pearls are often fairly large, due to the considerable size of the oyster. The natural dark colours of the pearls make them unique.

Tahitian pearls are a variety of shades – gray, silver, charcoal and so on. Truly black pearls are very rare and desirable. Despite their name, Tahitian pearls do not actually originate in Tahiti – this is the commercial centre and trading hub for the bulk of the industry, but does not have any pearl farms. The colour and size of Tahitian pearls make them a dramatic and beautiful organic gemstone for use in designer jewellery.


Keshi Pearls


Keshi pearls are formed by the oyster rejecting and spitting out the implanted irritant before the culturing process is complete. Because they have no nucleus, keshi pearls vary widely in shape and colour and, being 100% nacre, are especially lustrous and shiny. This makes them an especially beautiful gem to be used in handmade and designer jewellery. In fact, most keshi have greater lustre than even the best-quality cultured pearls. Visit Astley Clarke's Keshi Pearl Jewellery . They can form in either saltwater or freshwater and are generally quite small in size.

Although the mollusc rejects the nucleus of its own accord, keshis are not classified as natural pearls because they are a bi-product of the culturing process, not a natural occurrence from the beginning.

Once upon a time, keshi pearls, especially of the Tahitian and South Sea variety, were a cheap option, despite being beautiful and unique, because they formed relatively often. Nowadays however, as culturing technology has advanced, South Sea and Tahitian pearls are being x-rayed to see whether the nucleus has been rejected. If it has been, it is then re-inserted before a keshi pearl has a chance to form. This has made keshi pearls far rarer than they used to be and thus increasingly expensive.

The word ‘keshi' means ‘poppy seed' in Japanese, presumably describing their erratic shape, and as a result these pearls are often referred to as ‘poppy seed pearls'.