Amid the symphonic blockbusters regularly staged in the large museums of New York City, the special exhibitions mounted at the Frick Collection in three quiet, elegant rooms on the lower level of the museum offer visitors a welcome dose of chamber music. Striking in this regard was the summertime exhibition of works by the eighteenth-century Genevan artist Jean-Étienne Liotard, whose spare but penetrating portraits, character studies, and still lifes filled the Frick’s small space with a Mozartian blend of lightness and piercing exactitude. Liotard is perhaps best known today for his pastel figures redolent of genre painting, such as La Belle Chocolatière (ca. 1745; Dresden, Gemäldegalerie), but the exhibition at the Frick demonstrated his breadth as an artist, both in subject and in medium. His portraits ranged in scale from miniature busts to full-length figures posed in interior settings, and they were rendered in almost every two-dimensional medium that was possible for an eighteenth-century artist to use—watercolor on vellum and ivory; oil on canvas; chalk; pastel; and engraving, etching, and mezzotint printed both on paper and, in one amazing case, on satin. The sitters likewise extended across a broad social scale, from Liotard’s own middle-class family and friends to European...