At other times they are used to balance a composition, both in form and effect, to prevent the picture being divided into two distinct and diagonal portions, as evidenced in many of the pictures by Cuyp; on other occasions they are introduced solely for chiaroscuro effects, so as to enable the artist to place masses of dark upon light, and vice versa .
— from The Evolution of Photography With a Chronological Record of Discoveries, Inventions, Etc., Contributions to Photographic Literature, and Personal Reminescences Extending over Forty Years by Werge, John, active 1854-1890