A The pearl has always had a special status among the rich and powerful throughout history. For instance, women in ancient Rome went to bed wearing pearls so that, on waking, they could remind themselves how wealthy they were. Pearls used to have more commercial value than diamonds until jewellers learnt to cut gems. In Eastern countries such as Persia, ground pearl powder was used as a medicine to treat conditions including heart disease and epilepsy.

B Pearls can generally be divided into three categories: natural, cultured and imitation. When an irritant, such as a grain of sand, gets inside a certain type of oyster, mussel or clam, the mollusc secretes a fluid as a means of defence to coat the irritant. Gradually, layers accumulate around the irritant until a lustrous natural pearl is formed.

C A cultured pearl undergoes the same process. There is only one difference between cultured pearls and natural ones: in cultured pearls, the irritant is a bead made of ‘mother-of-pearl’ and is placed in the oyster through surgical implantation. This results in much larger cores in cultured pearls than in natural pearls. As long as there are enough layers of nacre, the secreted fluid covering the irritant, to create a gorgeous, gem-quality pearl, the size of the nucleus does not affect its beauty or durability.

D Pearls can come from both saltwater and freshwater sources. Typically, saltwater pearls are of high quality, although some freshwater pearls are considered high quality too. In addition, freshwater pearls often have irregular shapes, with a puffed-rice appearance. Nevertheless, individual merits determine a pearl’s value more than its source. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls, while most freshwater cultured pearls sold today come from China. There are several options for producing cultured pearls: using freshwater or saltwater shellfish, transplanting the graft into the mantle or the gonad, adding a spherical bead or using a non-beaded method.

E No matter which method is used to obtain pearls, the process usually takes several years. Mussels must reach maturity, which may take up to three years, and then have an irritant implanted. Once the irritant is in place, it takes approximately another three years for a pearl to reach its full size. Sometimes the irritant may be rejected. As a result, the pearl may be seriously deformed, or the oyster may die from complications such as disease. At the end of a five- to ten-year cycle, only half of the oysters may have survived. Among the pearls actually produced, only about 5% will be of sufficiently high quality for jewellery makers.

F Imitation pearls are a different matter. The island of Mallorca in Spain is renowned for its imitation-pearl industry. In most cases, a bead is dipped into a solution made from fish scales. However, this coating is quite thin and often wears off. One way to distinguish an imitation pearl is to bite it gently. Fake pearls glide smoothly across the teeth, whereas the layers of nacre on real pearls feel gritty.

G Several factors are taken into account when evaluating a pearl: size, shape, colour, surface quality and lustre. Generally, the three types of pearls rank in the following order of decreasing value: natural pearls, cultured pearls and imitation pearls, which are basically worthless. One way for jewellers to tell whether a pearl is natural or cultured is to send it to a gem laboratory for X-ray examination. High-quality natural pearls are extremely rare. Japan’s Akoya pearls are among the glossiest pearls available, while the South Sea waters of Australia produce larger pearls.

H Historically, the world’s highest-quality pearls were found in the Persian Gulf, particularly around Bahrain. These pearls had to be harvested by hand by divers without advanced equipment. Unfortunately, when large oil reserves were discovered in the early 1930s, the Persian Gulf’s natural-pearl industry came to a sudden end because contaminated water destroyed the once-pristine pearl beds. Today, India probably has the largest stock of natural pearls. Ironically, a large part of India’s stock of natural pearls originally came from Bahrain.