After the vases had been made on the wheel they were duly dried in the sun[773] and lightly baked, after which they were ready for varnishing and painting; it is evident that they could not be painted while wet and soft. Moreover the glaze ran best on a surface already baked. It is also probable that the glaze was brought out by a process of polishing, the surface of the clay being smoothed by means of a small piece of wood or hard leather. At all events this seems the most satisfactory interpretation of a vase-painting in Berlin (Fig. 67_a_),[774] where a boy is seen applying a tool of some kind to the outer surface of a completed vase (_kotyle_); that the vase is not yet varnished is shown by its being left in a red colour, while two others, varnished black all over, stand on the steps of an oven close by, probably to dry after the application of the varnish. [Illustration: FIG. 67. (_a_) CUP IN BERLIN WITH BOY POLISHING VASE; (_b_) HYDRIA IN MUNICH: INTERIOR OF POTTERY.] Many vases, whether decorated with designs or not, are varnished black throughout the exterior, except the feet and lips, and we cannot be certain whether or not any glaze had been previously applied to the surface; but in respect of the red-figured vases, it is clear from the method employed (see p. 221) that they were originally glazed throughout. This lustrous glaze is, like the black varnish, now quite a lost art. Seen under a microscope it has evidently been fused by baking; it yields neither to acids nor the blow-pipe. It is remarkably fine and thin, insomuch that it can only be analysed with great difficulty. No lead entered into its composition. It is however far inferior to modern glazes, being permeable by water; but it is not decomposed by the same chemical agents. On the later R.F. vases it is of decidedly inferior quality, and often scales away, carrying the superimposed colours with it.[775] 3. THE BAKING OF VASES The process of baking (ὀπτᾶν, _coquere_) was regarded as one of the most critical in the potter’s art. It was not indeed universal, as Plato[776] distinguishes between vases which have or have not been exposed to the action of fire (ἔμπυρα and ἄπυρα), and Pliny[777] speaks of _fictile crudum_ (ὠμόν) used for medicinal purposes. But all the vases that have come down to us have certainly been baked. The necessary amount of heat required was regulated by the character of the ware, and in the case of most Greek fabrics it appears to have been high. Many examples exist of discoloured vases which have been subjected to too much or too little heat, and in which the varnish has acquired a greenish or reddish hue. On the other hand, in some of those that have been subjected to subsequent burning, the red glaze has turned to an ashen-grey colour,[778] the black remaining unimpaired; but there are also instances of the varnish peeling off, the red colour alone preserving the outline of the figures.