"He (Apelles) passed a dark colour over his pictures when finished, so thin that it increased the splendour of the tints, while it protected the surface from dust and dirt: it could only be seen on looking into the picture. The effect of this operation, judiciously managed, was to prevent the colours from being too glaring, and to give the spectator the impression of looking through a transparent crystal. At the same time it seemed almost imperceptibly to add a certain dignity of tone to colours that were too florid." "This," says Reynolds, "is a true and artist-like description of glazing or scumbling, such as was practised by Titian and the rest of the Venetian painters."
The account of Pliny has, in this instance, internal evidence of truth, but it is fully confirmed by the following passage in Aristotle:—"Another mode in which the effect of colours is exhibited is when they appear through each other, as painters employ them when they glaze (ἐπαλειφοντες)127 a (dark) colour over a lighter one; just as the sun, which is in itself white, assumes a red colour when seen through darkness and smoke. This operation also ensures a variety of colours, for there will be a certain ratio between those which are on the surface and those which are in depth."—De Sensu et Sensili.
Aristotle's notion respecting the derivation of colours from white and black may perhaps be illustrated by the following opinion on the very similar theory of Goethe.
"Goethe and Seebeck regard colour as resulting from the mixture of white and black, and ascribe to the different colours a quality of darkness (σκιερὸν), by the different degrees of which they are distinguished, passing from white to black through the gradations of yellow, orange, red, violet, and blue, while green appears to be intermediate again between yellow and blue. This remark, though it has no influence in weakening the theory of colours proposed by Newton, is certainly correct, having been confirmed experimentally by the researches of