Artist Alexander Calder (1898–1976) is renowned for his whimsical sculptures and mobiles, but only a few admirers are aware that he also created several pieces of jewelry. Most were for his wife, Louisa, and for friends like Peggy Guggenheim, who commissioned him to make a pair of mobile earrings. This 1938 necklace—constructed of brass that had been beaten and twisted, a technique Calder often employed for his sculptures—was originally purchased by Kenneth Clark, the then director of the National Gallery in London, for his wife. Estate jeweler Russell Zelenetz, a co-owner of Madison Avenue’s Stephen Russell (212.570.6900), recently acquired the necklace from a private collector. "Calder jewelry is extremely rare," says Zelenetz. The jeweler has handled countless historic pieces, yet this intricate arrangement of spirals and coils is one of the most fascinating he has ever seen. "At first glance, it appears like it could be ancient—tribal, Greek, or Etruscan," he says. "But at the same time, it has the feel of pop art."