John Chaloner Smith, British mezzotinto portraits, being a descriptive catalogue of these engravings from the introduction of the art to the early part of the present century : arranged according to the engravers, the inscriptions given at full length, and the variations of state precisely set forth : acc , Martino Pub., Mansfield Centre, CT, 2004, v.2, p. 916, Marchi no. 13, NE1816.G7 S58 2004Mary Webster, Johan Zoffany, 1733-1810, National Portrait Gallery, London, 1976, p. 41, no. 37, NJ18 Z68 W43 (YCBA)