imperfections is also important in determining value. A South Sea pearl can often be mounted in a way that will hide its flaws when worn. This means if you select your pearl(s) carefully, you can have a clean-looking one for a lower price. Remember that blemishes on single pearls tend to be more obvious than on those in strands. Therefore, when buying a loose South Sea pearl, figure out in advance how you will wear it so you can choose

one whose flaws won't be noticeable.

SIZE: South Sea pearls generally range in size from 9 to 19 mm. The size of semi-round pearls is indicated by the average diameter or by the smallest measurement of the diameter. The size of baroque pearls is most accurately represented by stating the length, width and height. However, sometimes only the two largest measurements are given.

The world's largest round South Sea pearl is 24 nun. Baroque pearls can have greater length measurements than round ones. A pearl belonging to the collection of Golay Buchel, has a length of 25 mm and weighs 90.6 ct. It's their large size that makes South Sea pearls so expensive. As would be expected, the larger the pearl the greater its value.

The size of a cultured pearl is primarily determined by the size of its bead nucleus. The bigger the oyster, the bigger bead it can accept and the bigger pearl it can grow. Consequently, small Japanese oysters which measure 4 inches (10 cm) across, produce smaller pearls than the silver or gold-lip oysters which can measure 12 inches (30 cm) across. Black-pearl oysters, which also produce white pearls, grow up to about 8 inches (20 cm) across and produce a pearl in between the size of the silver-lip and Akoya oysters.

South Sea pearl strands aren't normally sold in the same 1/2 mm increments as Akoya pearls. They're usually graduated with larger pearls in the center and smaller pearls on the ends. It's very difficult to find matched South Sea pearls of one size. In addition, it's not cost effective to place large pearls at the back of the neck where they aren't necessarily seen. Consequently, it's best to give a size range when asking for South Sea pearl strands-for example, 12-14 mm. The most typical Australian South Sea strand size is probably 11-13 or 14 mm. Dealer's will do special strand layouts such as 12-13 mm or 14-15 mm on request. But these are costly, and a deposit may be required before the dealer will make up the strand.

NACRE THICKNESS:  Big pearls do not necessarily have thick nacre. As with Akoya pearls, the nacre thickness of cultured South Sea pearls has decreased during the past 30 years. In the April 1971 issue of Lapidary Journal, Australian pearl farmer C. Denis George stated that a good cultured South Sea pearl had a nacre thickness double the radius of the bead nucleus. In other words, a 15-mm pearl had about a 5-mm nacre thickness and a nucleus whose radius is about 2.5 mm. If this standard were used today, it would be very hard to find a good South Sea pearl. Judging from standards published by black pearl producers, South Sea pearls today should have a nacre thickness of at least 1 mm of the radius.

One millimeter may sound thick compared to the minimum standard this book suggests for Akoya pearls-0.35 mm. Keep in mind, though, that Akoya pearls have a finer-grained nacre than South Sea pearls and they are smaller. A 0.5-mm thickness on a 6-mm Akoya pearl is 1/6 of the radius. A 1-mm thickness on a 12-mm South Sea pearl is also 1/6 of the radius. Therefore, it's reasonable for buyers to expect nacre at least 1 mm thick on their South Sea pearls, especially considering their high cost.