As regards pigments, then, a proper mixture of yellow, red, and blue; or of yellow and purple, red and green, or blue and orange; or of orange, green, and purple, affords black if sufficiently intense, and grey if sufficiently diluted. The black may be rendered grey by spreading a thin wash over a white ground, or by the direct addition of white. It must be remembered, however, that suitable proportions of the component colours are essential. When all three of the primaries, for example, are mixed together, colour is neutralised according as they are compounded of equal strength and in right quantities: if proper proportions are observed, pure black or normal grey results; but if not, there will be produced a coloured black or a coloured grey, an excess of one or two of the primaries giving rise to brown, marrone, or gray. A reference to the lists of permanent primary and secondary pigments will show to what extent durable greys can be compounded. As these pigments differ so widely in hue and other properties, no fixed rules can be given for their admixture: to ensure neutrality, practice and a correct eye are indispensable. Without perfect neutrality, difficult to attain and rarely to be met with, grey ceases to exist. In pure white, pure grey, and pure black, colour is, so to speak, conspicuous by its absence. CHAPTER XXI. ON THE NEUTRAL, BLACK. Black is the last and lowest in the series or scale of colours descending--the opposite extreme from white--the maximum of colour. To be perfect, it must be neutral with respect to colours individually, and absolutely transparent, or destitute of reflective power as regards light; its use in painting being to represent shade or depths, of which black is the element in a picture and in colours, as white is of light. As there is no perfectly pure and transparent black pigment, black deteriorates all colours in deepening them, as it does warm colours by partially neutralizing them, but it combines less injuriously with cold colours. Though black is the antagonist of white, yet added to it in minute portion, it in general renders white more neutral, solid, and local, with less of the character of light. Impure black is brown, but black in its purity is a cold colour, and communicates a coolness to all light colours; thus it _blues_ white, _greens_ yellow, _purples_ red, and _cools_ blue. Hence the artist errs with ill effect who regards black as of nearest affinity to hot and brown colours, and will do well to keep in mind--"The glow of sunshine and the _cool_ of shade."