The irregular construction of the Chinese kilns resulted in a great variety of firing conditions, of which the Chinese potter made good use; so that, by a judicious arrangement of the wares, glazes which required a comparatively low temperature were fired in the same kiln as those which needed the same heat as the porcelain body itself. The glazes just enumerated are familiar from the large covered jars, vases, garden seats, etc., with designs raised, carved, or pierced in outline, many of which date from the fifteenth century.[227] Their manufacture continued throughout the Ming period, both in porcelain and pottery, and in the latter, at any rate, continued into the Ch’ing dynasty.
Another group of glazes applied likewise to the biscuit and fired in the temperate parts of the kiln differs from the last mentioned in its greater translucency.[228] These are the san ts’ai or three colours, viz. green, yellow and aubergine, all of which contain a considerable proportion of lead, and differ little in appearance from the on-glaze enamels of the muffle kiln. They were used either as monochromes, plain or covering incised designs, or in combination to wash over the spaces between the outlines of a pattern which had been incised or painted on the biscuit.
Finally, the enamels of the Wan li wu ts’ai,[229] overglaze colours used in addition to underglaze blue, were composed of a vitreous flux coloured with a minute quantity of metallic oxide. The flux, being a glass containing a high percentage of lead, was fusible at such a low temperature that it was not possible to fire them in the large kiln. Consequently these enamels were painted on to the finished glaze, a process which greatly increased the freedom of design, and fired in a small “muffle” or enameller’s kiln, where the requisite heat to melt the flux and fix the colours could be easily obtained.
Though the T’ao shuo, in the section dealing with Ming technique, makes a general allusion to painting in colours on the glaze, the only specific reference to any colour of the muffle kiln, excepting gold, is to the red obtained from sulphate of iron (fan hung sê). This, we are told, was made with 1 oz. of calcined sulphate of iron (ch’ing fan) and 5 oz. of carbonate of lead, mixed with Canton ox-glue to make it adhere to the porcelain before it was fired. This is the iron red, the rouge de fer of the French, which varies in tint from orange or coral to deep brick red, and in texture from an impalpable film almost to the consistency of a glaze, according to the quantity of lead flux used with it. On the older wares it is often deeply iridescent and lustrous, owing to the decomposition of the lead flux. This fan hung is the colour which the Chia Ching potters were fain to substitute for the underglaze copper red (chi hung) when the usual material for that highly prized colour had come to an end, and difficulty was experienced in finding an effective substitute.
The remaining colours of the on-glaze palette are more obviously enamels; that is to say, glassy compounds; and as they were, in accordance with Chinese custom, very lightly charged with colouring matter, it was necessary to pile them on thickly where depth of colour was required.
Hence the thickly encrusted appearance of much of the Chinese enamelled porcelain. The Wan Li enamels consisted of transparent greens of several shades (all derived from copper), including a very blue green which seems to have been peculiar to the Ming palette, yellow (from antimony) pale and clear or brownish and rather opaque, and transparent aubergine, a colour derived from manganese and varying in tint from purple to brown. Two thin dry pigments—one an iron red and the other a brown black colour derived from manganese—were used for drawing outlines; and the brown black was also used in masses with a coating of transparent green to form a green black colour, the same which is so highly prized on the famille noire porcelains of the K’ang Hsi period. As for the blue enamel of the K’ang Hsi period, it can hardly be said to have existed before the end of the Ming dynasty.[230]
Gilding, which was apparently in use throughout[231] the Ming period, was applied to the finished porcelain and fired in the muffle kiln. The gold leaf, combined with one-tenth by weight of carbonate of lead, was mixed with gum and painted on with a brush. The effect, as seen on the red and green bowls (Plate [74]), was light and filmy, and though the gold often has the unsubstantial appearance of size-gilding, in reality it adheres firmly[232] and is not easily scratched.
Of the other processes described in the T’ao shuo,[233] embossed (tui
) decoration was effected by applying strips or shavings of the body material and working them into form with a wet brush. Some of the more delicate traceries, in scarcely perceptible relief, are painted in white slip. Engraved (chui