COBALT BLUE MONOCHROME GLAZES.--We may distinguish three varieties of blue derived from cobalt, but the full sapphire of the blue and white ware is not found as a monochrome glaze:--
1. The _Clair de lune_. The term _yueh-pai_, or moon-white, was applied to more than one class of Sung porcelain, but above all to the Ju yao. In later times, when these primitive wares were copied, the colour was given by a minute quantity of cobalt, but it is very doubtful whether that pigment was known in early Sung days. The _clair de lune_ glazes of Nien were considered second in merit only to the copper reds of that great viceroy. The uncrackled glazes of this class are often classed as celadon.
2. The Mazarin blue, known also as _bleu fouetté_ or powder-blue.[89] This glaze is blown on to the surface of the raw paste, in the manner described on page 30. It sometimes covers the whole surface, and is then generally decorated with floral designs in gold, but more often it forms the ground for vases and plates with large white reserves on which designs in enamel colours are painted.
3. The _Gros Bleu_, in the form of large plates and vases, was a great favourite with the Arabs and other Mohammedan races. This ware, too, was often covered with a decoration of gold. There is a magnificent plate of this class in the British Museum, and at South Kensington, in the India Museum, a tall, dark-blue vase which we have already mentioned. From Persia come many specimens of this deep blue ware, of a greyish or even slaty tint, decorated, like the _fond laque_, with flowers in a white slip.
BLACK GLAZES.--Very near to this last class of blue glazes we may place the ‘metallic black,’ the _wu-chin_ of the Chinese. According to the Père D’Entrecolles, this mirror-black is prepared by mixing with a glaze containing much lime and some of the same ochry earth that gives the colour to the brown glazes, a sufficient quantity of cobalt of poor quality. In this case no second glaze is required, and the vessel is fired in the _demi grand feu_, _i.e._ in the front of the furnace. Other blacks are painted on and covered with a second glaze. The large spherical vases with tall tubular necks show little trace generally of the gold with which the black glaze was originally decorated.
