It would appear that the vases after the baking were often placed on the exterior of the furnace, either to prevent the too rapid cooling of the clay, or (as indicated on the Berlin cup) for the pigments to dry. Jahn and others have published a gem[789] on which a small two-handled vase is placed on the top of an oven, and a youth is applying two sticks to it, perhaps in order to take it down without injury by the contact of the hand. A companion gem,[790] on which an artist is painting a similar jar, shows a jug and a kylix standing on a kiln. When the vases were returned from the furnace, the potter appears to have made good as far as possible the defects of those not absolutely spoiled; and if naturally or by accident any parts remained too pale after the baking, the defect was remedied by rubbing them over with a deep red ochre, which supplied the necessary tone. 4. PAINTING We may distinguish three principal classes of painted pottery, of which one at least admits of several subdivisions:— (1) Primitive Greek vases, with simple painted ornaments, chiefly linear and geometrical, laid directly on the ground of the clay with the brush. The colour employed is usually a yellowish or brownish red, passing into black. The execution varies, but is often extremely coarse. (2) Greek vases (and Italian imitations) painted with figures. These may be subdivided as follows:— (_a_) Vases with figures in black varnish on red glazed ground (see Frontispiece, Vol. II.); (_b_) Vases with figures left in the red glaze on a ground of black varnish (see Frontispiece, Vol. I.). (3) (_a_) Vases of various dates with outline or polychrome decoration on white ground (see Plate XLIII.); (_b_) Vases (also of various dates) with designs in opaque colour on black ground. Of these, the second group is by far the largest and most important, and the complicated and technical processes which it involved will demand by far the greater share of our attention in the following account of the methods of painting. In both the classes (_a_) and (_b_) the colouring is almost confined to a contrasting of the red glazed ground of the clay with a black varnish-like pigment, a contrast which perhaps more than anything else furnishes the great charm of a Greek vase.