Jean-Étienne Liotard 
(1702- 1789)
 

Jean-Étienne Liotard was a Genevan painter, pastellist, printmaker, art theorist and art dealer. Born in the Republic of Geneva as the son of exiled French Huguenots, he spent most of his career working in cities such as Rome, Istanbul, Paris, Vienna, London, Amsterdam and other cities. He is best known for his detailed, strikingly naturalistic portraits in pastel and Orientalist scenes of life in Turkey. As an art theorist he wrote the Traité des Principes et règles de la Peinture (Treatise on the Principles and Rules of Painting) in which he argued that painting should to be a mirror of nature.

https://en.wikipedia.org/wiki/Jean-Étienne_Liotard

Portrait of John, Lord Mountstuart, later 4th Earl and 1st Marquess of Bute
Pastel, on vellum
114.9 × 90.2 cm
The J. Paul Getty Museum, Los Angeles, United States
https://www.getty.edu/art/collection/object/108GFH

Jean-Étienne Liotard depicted the charismatic English nobleman in an elegant setting--a re-creation of a salon in Geneva appointed with Rococo furnishings such as firedogs ornamented with cherubs and a Chinese folding screen used to stop cold drafts. Above the mantel, Liotard depicted Mountstuart's handsome profile and dignified posture in a gilded mirror.