We learn from these relations of colours, why dapplings of two or more produce effects in painting so much more clear and brilliant than uniform tints obtained by compounding the same colours: and why hatchings, or a touch of their contrasts, thrown as it were by accident upon local tints, have the same effect. We see, too, why colours mixed deteriorate each other, which they do more--in many cases--by imperfectly neutralizing or subduing each other chromatically, than by any chemical action. Finally, we are impressed with the necessity, not only of using colours pure, but of using pure colours; although pure colouring and brilliancy differ as much from crudeness and harshness, as tone and harmony from murkiness and monotony. The powers of colours in contrasting each other agree with their correlative powers of light and shade, and are to be distinguished from their powers individually on the eye, which are those of light alone. Thus, although orange and blue are equal powers with respect to each other, as regards the eye they are totally different and opposed. Orange is a luminous colour, and has a powerfully irritating effect, while blue is a shadowy colour, possessing a soothing quality--and it is the same, in various degrees, with other colours. There are yet further modes of contrast or antagonism in colouring, which claim the attention and engage the skill of the colourist. Of the contrast of _hues_, upon which depend the brilliancy, force, and harmony of colouring, we have just spoken; but there is, secondly, the contrast of _shades_. To this belong all the powers of chiaroscuro, by which term the painter denotes the harmonious effects of light and shade; and though they form the simplest part of colouring, yet they cannot be separated from it--light and shade, the chiaroscuro, being a distinct and important branch of painting. A third mode of contrast in colouring is that of _warmth_ and _coolness_, upon which depend the toning and general effect of a picture. Fourthly, there is the contrast of _colour_ and _neutrality_, the chromatic and achromatic, or hue and shade. By the right management of this, local colours acquire value, gradation, keeping, and connection: whence come breadth, aërial perspective, and the due distribution of greys and shadows in a picture.