"Variation in dark and light is called value. Value can be a natural part of any object, or it can be created by controlling the way in which light strikes the object. Artists can vary value in color by adding black or white, or by selecting contrasting dark or light color values. Sculptors create value by the way they form the surface to catch light and cast shadows. In all ages, and in many materials, artists have created value contrasts. Their creations have enriched the world of dark and light we see around us." - Summary from Worldcat.