“It’s amazing anytime we get a piece from the duchess’s collection. But these are really works of art.”   Chalcedony, the quartz that composes these pale-blue bracelets, is an unusually humble material for rarefied, auction-worthy jewelry. “Chalcedony is really a dive material,” says Frank Everett, vice president and sales director for Sotheby’s jewelry, which sold the cuffs Dec. 9 in New York City. “And there isn’t a lot of diamond and sapphire in the [pieces]. They’re such a fabulous example of when the design and provenance of a piece is the value, not the materials.” The cuffs were designed in the mid-1930s for the Duchess of Windsor, one of history’s most stylish women, by the late French designer Suzanne Belperron—who was once obscure, but has become a favorite among serious collectors in recent decades. “I love a flawless diamond as much