Ponsonby first encountered Liotard at Rome in 1738 and took him as his draughtsman to Constantinople, where the artist’s independent career began. He remained a loyal friend and patron, eventually owning some 70 works by Liotard. This portrait was presumably made during one of Liotard’s two sojourns in London. It is one of Liotard’s rare excursions into Neoclassicism, and presents the sitter as a trompe l’oeil Roman shell cameo.