....To compare these two portraits with one Copley painted in 1758—that of Mary and Elizabeth Royall —is to understand why Copley so quickly put other portraitists out of business. These young daughters of Isaac Royall (a much younger Mary can be seen in Robert Feke’s 1741 portrait of Isaac Royall and Family) wear shimmering velvet gowns, Copley has painted their faces to show not only what they looked like, but to display a sense of their personality, too. Mary displays a hummingbird that is perched on her finger, while the younger Elizabeth pets a King Charles spaniel. Their gowns, the curtain and column in the background, and the inclusion of rare (a hummingbird) and royal (the King Charles spaniel) animals makes this a compositionally daring and visually interesting image. And Copley was then only 20 years old. (https://www.khanacademy.org/humanities/art-americas/british-colonies/colonial-period/a/copley-a-boy-with-a-flying-squirrel)