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 artists of Art Nouveau ever. And it has every element that you think of when you think of the movement.”