The most important feature of the Sung wares lies in their glaze, which holds _la qualité maîtresse de la céramique_, as an enthusiastic French writer has expressed it. Its richness, thickness, lustre, translucency, and its colour and crackle are the main criteria of the wares in the eyes of Chinese connoisseurs. _Tzŭ jun_ (rich and unctuous), _hsi ni_ (fine and glossy), _jung_ (lustrous), _t´ung jung_ (lustrous throughout or transparent) are among the phrases most constantly met in their appreciations. A word, too, is usually added on colour of the body material, which in many cases would appear to have been of a red or brown tint, iron-coloured or copper-coloured. Not that it is necessary to infer that in every instance the ware was red or brown throughout. It is a matter of observation that in many of the early wares the exposed places (usually confined to the edge of the foot rim or the unglazed base) have assumed a rusty red colour in the firing, while a flake broken from the glaze elsewhere reveals a white or greyish white porcelain body within. This will often explain the seeming inconsistency of the Chinese descriptions in which the word porcelain is applied to an apparently dark-coloured material. At the same time, it is well to remember that the Chinese words which we translate as porcelain were far more comprehensive than our own term. Our speculations on the nature of the Ch´ai ware in a previous chapter brought us face to face with two main types of glaze, the thick opalescent glaze of pale lavender or turquoise tint, and the smooth translucent celadon glaze in which green is the dominant colour. These types are prominent on the Sung wares, and almost all the varieties of coloured Sung glazes--with such obvious exceptions as black and chocolate brown--have more or less affinity to these two. So that if we place the old turquoise[91] glaze at one end of the series and the green celadon at the other, the rest will find an intermediate place, with leanings, of course, towards one or other of the extremes. One of the puzzling features in the study of the Sung wares is the interrelation of the various makes, such as the Ju, Kuan, Ko, Lung-ch´üan, Tung ch´ing and Chün, which all appear to have had points of mutual resemblance, although the descriptions of individual specimens differ over a wide range. If, however, it can be assumed that the same fundamental principles of manufacture were observed in all these factories, and that the divergences in the wares arose from local conditions, such as variety of clays, different conditions of firing and slight variations in the composition of the glaze, a formula is established which will cover most of our difficulties. I am assured by no less an authority on glazes than Mr. W. Burton[92] that this assumption is perfectly justifiable, and that one and the same glaze might emerge from the kiln as a celadon green, a grey green, dove grey, lavender grey,