He spent the 1790s based in Rome, where he bought much art; this was sold for a considerable profit in 1801 after his return to London.
In 1791 he went to Italy, and stayed there ten years, studying art and collecting pictures, drawings, and prints, profiting from the turmoil of the French invasion.
Paintings in his collection included The Mystical Nativity by Botticelli and Raphael's Vision of a Knight, both now in the National Gallery.
In the same year he was appointed Keeper of the Department of Prints and Drawings in the British Museum, a post he retained till his death in 1836.
Besides these works, he published in 1801 a catalogue of Italian pictures, which he had acquired during his stay in Italy from the Colonna, Borghese, and Corsini Palaces; A Descriptive Catalogue of the Pictures in the National Gallery, 1826; and Observations on a MS. in the British Museum, in a controversy concerning Cicero's translation of an astronomical poem by Aratus.