In considering the colours used in the decoration, we naturally take first the limited number which were developed in the full heat of the porcelain furnace, the _couleurs de grand feu_ of the French classification. These were either incorporated in the glazing material or painted on the porcelain body and protected by the glaze. Chief among them was blue, which we have already discussed in its various qualities. The Mohammedan blue--the _su-ni-p’o_ of the Hsüan Tê period and the _hui hui ch’ing_ of the reigns of Chêng Tê and Chia Ching--was an imported material of pre-eminent quality but of uncertain supply. It was supplemented--and, indeed, usually blended--with the native mineral[222] which was found in several places. Thus the _po-t’ang_ blue (so called from a place name) was found in the district of Lo-p’ing Hsien in the Jao-chou Fu; but the mines were closed after a riot in the Chia Ching period, and its place was taken by a blue known as _shih-tzŭ ch’ing_ (stone, or mineral, blue) from the prefecture of Jui-chou in Kiangsi. According to Bushell[223] the _po-t’ang_ blue was very dark in colour, and it was sometimes known as _Fo t’ou ch’ing_ (Buddha’s head blue) from the traditional colour of the hair of Buddha. Another material used for painting porcelain was the _hei chê shih_ (black red mineral) from Hsin-chien in Lu-ling, which was also called _wu ming tzŭ_. It was evidently a cobaltiferous ore of manganese and a blue-producing mineral, doubtless the same as the _wu ming i_ (nameless wonder), which we have already found in use as a name for cobalt. Much confusion exists, in Chinese works, on the subject of these blues, and it is stated in one place that the “Buddha head blue” was a variety of the _wu ming i_, which would make the _po t’ang_ blue and the _wu ming i_ and the _wu ming tzŭ_ one and the same thing. In effect they were the same species of mineral, and the local distinctions are of no account at the present day except in so far as they explain the variety of tints in the Ming blue and white. It is, however, interesting to learn from a note on Mohammedan blue in the K’ang Hsi Encyclopædia that the native mineral, when carefully prepared, was very like the Mohammedan blue in tint.