Art Nouveau’s emphasis on flowing lines, femininity, and natural forms is perfectly ­embodied in this late-19th-century brooch from Parisian ­jeweler Georges Fouquet.It sold for $154,384—more than six times its high estimate—at Sotheby’s Dec. 11 London auction, the Jewellery Collection of the Late Michael Wellby: An Eclectic Eye.Featuring a woman’s face, headdress, and flowing locks carved from chalcedony, the precious gem–accented pin is colored with plique-à-jour enamel; the technique lends the piece the transparency of stained glass and “is very difficult to work with because it can look lumpy,” says Alexandra Rhodes, a senior international jewelry specialist for Sotheby’s. Rhodes—who recalls that bidding for the intricate brooch was lively, inciting a flurry of activity both in the room and on the phones—says the signed piece was made by “one of the great a