This latter deficiency was due to the use of flat colours, which did not allow of shades, and the figures were consequently not seen in masses distinguished by light and shade, but isolated in the air. Hence, in order to make the figures distinct, and to express by attitude all the actions and sentiments required, the artist was compelled to use profile. The black colour, the choice of which may at first appear singular, is, after all, the most harmonious, and the best suited for showing the elegance and purity of the outline; whilst by its aptness to reveal any defects of shape, it compelled the artist to be very careful in his drawing. The colours employed[805] were, as we have seen, remarkably few in number. Of the black varnish which plays such an important part, and of its composition we have already spoken. Of the opaque accessory colours, the white is said by Brongniart[806] to be a carbonate of lime or fine clay. It is evidently an earth of some kind, and gives no trace of lead under analysis. The creamy slip of the white-ground vases is of similar character, and appears to be a kind of pipeclay. It was probably of the same character as the earth of Melos used by Polygnotos.[807] The deep purple or crimson, so largely employed on the Corinthian and early Attic B.F. vases, is known to be an oxide of iron, an element which entered largely into the red glaze. The yellow found on the white vases and those of Apulia as an accessory to white is of an ochrous nature. The red used for outlines on the white lekythi is probably not vermilion (_minium_), but red ochre (μίλτος, _rubrica_). Blue and green, which are rarely found, and only on vases of the later styles, were produced from a basis of copper. On vases from the time of Euphronios and Brygos (about 480 B.C.) onwards, gilding was occasionally employed, the process being one which we have already described (see above, p. 210). Good instances of this process are to be seen in the fourth-century vases from Capua, which are glazed black throughout and ornamented solely with gilding.[808] But the gold leaf has often perished. Besides Capua, these vases are found chiefly in Athens and the Cyrenaica. 5. STATUS OF POTTERS