Fran?ois Tronchin, 1757. This magnificent pastel depicts Fran?ois Tronchin, a prominent figure in his native Geneva and an impassioned patron of the arts. On the table are a book, mathematical instruments, and papers that indicate his taste for architecture and music. Rembrandt's Lady in Bed, about 1645-46 (Scottish National Gallery), the most highly prized painting in Tronchin's collection, rests on an easel. Liotard considered the portrait of Tronchin among his finest works. Indeed, the meticulous rendering of the sitter's powdered wig, transparent flesh, and lace cuffs, accompanied by the conjuring of the subtle grace of the Dutch master's nude, attest to the pastelist's consummate skill.