Value gives the artist the means of showing subtle changes in a form's surface-state, and it helps clarify the relative distance between forms.
Nathan GoldsteinThe local-tone is the intrinsic value of a thing - excluding any effects of light. The local-tone of a common pearl is very nearly white; that of a lump of coal, nearly black.
Nathan GoldsteinThe inherent lightness or darkness of a form - its local-tone - is a given quality of all forms. It is affected by, but separate from, the light and dark areas that result from light falling on forms.
Nathan Goldstein