Found in the Wellcome Institute Library within a pile of portrait prints and drawings of Americans. The only 18th-century American artist recorded by the National Portrait Gallery, Washington D.C., as having painted in oil on copper is John Singleton Copley (1738-1815): most of his oil on copper miniatures were painted in the 1750s and 1760s, and they do not appear to resemble the present work (letter to the Wellcome Institute, 20 October 1993, from Linda Thrift, Keeper, Catalog of American portraits, The National Portrait Gallery, Smithsonian Institution)