In painting, however, as already remarked, mere light and darkness only supply the fundamental basis, albeit such a foundation is of the greatest importance. For it is this contrast and only this which defines the comparative prominence and retirement, the rondure, and generally the actual appearance of form as sensuous shape, all that we understand by _modelling._ Masters of colour in this respect simply carry the process to the most extreme contrasts of the most brilliant light and the deepest shadow, and merely produce thereby their grand effects. Such contrasts are, however, only permissible in so far as they avoid harshness, that is, in so far as they are made within the limits of a just interplay of intermediate tones and colour transitions, which bind the entire composition in a fluid unity and render the finest gradations of tint possible. If such contrasts are entirely absent the entire effect will be flat, because it is precisely this distinction between that which is more brilliant and more obscure which gives emphatic prominence to particular aspects of the work and a like subordination to others. And especially in the case of compositions having a large content, and where the distance between objects is considerable, it is necessary to introduce the deepest shadow in order to make the scale of light and shadow a broad one.
With regard to the closer definition of light and shade we find that this depends more than anything else upon the mode of _lighting_ accepted by the artist. The light of day, that of morning, noon, and evening, sunlight or moonlight, a clear or clouded sky, the light of tempest, candle-light, a light that is veiled, or falls upon the object or diffuses itself gradually, every conceivable mode of lighting, in short, is possible, and the cause of every kind of effect. In treating a subject of public interest, full of incident, a situation that at once appeals to our common sense, the question of external lighting is of subordinate importance. The artist will avail himself here with most advantage of ordinary daylight, if, that is, the demands of dramatic vividness, and a desire to emphasize particular figures and groups, or to throw into the background others, do not render a less usual mode of lighting necessary, which may fall in more readily with such objects.