(Photo credit: Davies + Starr; interior pearls courtesy of Albert Asher South Sea Pearl Co.)

It took pearl dealer Salvador Assael ten years to assemble what he calls “the Ultimate Necklace”—23 gumball-size South Sea pearls that illuminate the wearer’s face like klieg lights. Handpicked by Assael at Australian farms, each pearl is at least 19 mm. wide, and the largest is 21 mm. If the necklace were on the market, its cost might match the highest auction price for a single strand of pearls—$2.3 million. Here, we explain what makes it so valuable. Inside the necklace: a pearl glossary.

Shape
Very few pearls actually come out of an oyster perfectly round. But they can be cultivated: After nucleation, oysters are moored to rafts in quiet bays, where they’re cleaned regularly to encourage the pearl to develop as a perfect sphere.

Size
Important, but not exclusively so. A perfectly formed smaller pearl might fetch a higher price than a slightly flawed larger one. If all else is equal, the larger pearl will be the more valuable. Unlike diamonds, pearls are not static gems; they are “alive” and can change with time, so caring for them is crucial.

Color
The color of a pearl is a function of the oyster and its nacre, although dye can be added to certain varieties after harvesting. Blinding white is still the most prized, but there’s plenty of choice, from rare gold and Tahitian “black” pearls to less costly freshwater pearls, which come in everything from pale tangerine to frosty pink.

Luster
The main factor in making a pearl shine is nacre—calcium-carbonate crystals secreted by oysters to form the inside of their shells. A sphere of mother-of-pearl from a United States freshwater mollusk is implanted in an oyster’s sex organs, where it’s hard to expel. If the oyster accepts the implant, it produces thousands of layers of nacre in an attempt to soothe the irritation.

Orient
While luster refers to the surface layers of nacre, the deeper glow of a pearl is derived from light refracted by the staggered layers of nacre crystals—each just microns thick—farther inside. A pearl with fiery orient seems to glow from within.

Related:

• Archive: “The Everything Guide”
• Table of Contents: May 9, 2005 issue of New York | Subscribe!