But none of these glazes can with strict accuracy be described as monochromes "of uniformly pure colour" which the _Po wu yao lan_ seems to have regarded as indispensable in the first-class Chün ware. In fact, it is difficult to conceive the possibility of a Chün glaze of perfectly uniform tint, without any trace of the perpetual war waged in the kiln between the red, grey, and blue elements. The nearest approach to a single colour is seen in some of the grey glazes, but here, too, the colour is only relatively pure; and I am convinced that the expression used by the _Po wu yao lan_ is exaggerated, and the meaning is that the nearer the Chün colours approach to uniformity the more they were prized. It is true that several examples depicted in Hsiang's Album are monochrome purple, but I have no more confidence in the colouring of these illustrations than in the carved decoration which is indicated under their glaze, a phenomenon unrecorded in any other Chinese work, unexampled in any known specimen of the ware, and unlikely in view of the nature and the thickness of the Chün glaze itself. It is clear, however, that an exaggerated mottling of the glaze and a confusion of many colours was viewed with disfavour by the old Chinese connoisseurs. These effects were explained in the _Po wu yao lan_ as due to insufficient firing. Regarded in this light they were viewed with contempt by the earlier Chinese writers and labelled with mocking names, such as _lo kan ma fei_ (mule's liver and horse's lung), pig's liver, and the like. In reality, they were the forerunners of the many delightful _flambé_ glazes which the eighteenth-century potters were able to produce at will when they had learnt that, like all the Chün colours except the brown glaze on the base, they could be obtained from oxide of copper under definite firing conditions. How far the old Chün effects were due to opalescence[259] it is impossible to say, but we know that all of them can be obtained, whether turquoise, green, crimson, or lavender grey, by that "Protean medium," oxide of copper, according as it is exposed in the firing to an oxidising or reducing atmosphere, conditions which could be regulated by the introduction of air on the one hand, or wood smoke on the other, at the right moment into the kiln. It should be added that the finer Chün wares as seen in the flower pots and stands have an olive or yellowish brown glaze over the base, which in rare instances is overrun by frothy grey or lavender. Another constant feature of these pieces is a ring of small scars or "spur marks" on the base. [Illustration: Fig. 1 Fig. 2 Plate 37.--Chün Chou Ware with porcellanous body (_tz´ŭ t´ai_). Sung dynasty. Fig. 1.--Flower Pot, with lavender grey glaze. Numeral mark, _ssŭ_ (four). Diameter 8¾ inches. _Eumorfopoulos Collection._ Fig. 2.--Bulb Bowl, of quatrefoil form, pale olive glaze clouded with opaque grey. Numeral mark, _i_ (one). Length 10 inches. _Freer Collection._]