Chiaroscuro, to use untechnical language and to speak of it as it is
employed by all the schools, is the art of making atmosphere visible
and painting objects in an envelope of air. Its aim is to create all the
picturesque accidents of the shadows, of the half-tones and the light,
of relief and distance, and to give in consequence more variety, more
unity of effect, of caprice, and of relative truth, to forms as to
colours. The opposite conception is one more ingenuous and abstract, a
method by which one shows objects as they are, seen close, the
atmosphere being suppressed, and in consequence without any perspective
except the linear perspective, which results from the diminution in the
size of objects and their relation to the horizon. When we talk of
aeriel perspective we presuppose a certain amount of chiaroscuro.
_Fromentin._