Lewis, D. (1984). Pencil drawing techniques. Watson-Guptill Publications.
Lua i Stíl Chicago (17ú heag.)Lewis, David. Pencil Drawing Techniques. New York: Watson-Guptill Publications, 1984.
Lua MLA (9ú heag.)Lewis, David. Pencil Drawing Techniques. Watson-Guptill Publications, 1984.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.