the physical nature and appearance of colours, it must be admitted that the latter sustains the above comparison with advantage; and it is somewhat extraordinary that observations indicating so refined a knowledge of nature, as regards the picturesque, should not have been taken into the account, for such appears to be the fact, in the various opinions and conjectures that have been expressed from time to time on the painting of the Greeks. The treatise in question must have been written when Apelles painted, or immediately before; and as a proof that Aristotle's remarks on the effect of semi-transparent mediums were not lost on the artists of his time, the following passage from Pliny is subjoined, for, though it is well known, it acquires additional interest from the foregoing extracts.
"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,