The English word ‘glaze’ is only another form of the word ‘glass,’ and we may say at once that, in composition at least, there is often little difference between the two substances. The French word for ‘glaze’ is _couverte_ or _vernis_; the last term applies well to the thin skin of glaze found on Greek pottery. The Chinese have several expressions, but it is a curious fact that the characters with which most of these terms are written contain the radical for ‘oil,’ and indeed the word ‘oil’ itself is often used in the sense of ‘glaze.’ Mr. Rix puts it well when he says that the glaze is to the enameller of porcelain what his canvas is to the painter; while in the case of a decoration ‘_sous couverte_,’ the glaze corresponds to the varnish which, while protecting his work, gives brilliancy to the colouring (_Journal of Society of Arts_, vol. xli.). It is, moreover, the vehicle by which the design is harmonised and rendered mellow. The effect is produced at once and endures practically for all time. The hardness and fusibility of glazes differ widely, and they are conditioned by the nature of the wares that they cover. It is evident that there must be a close relation between the fusing-points of paste and glaze, and that the latter should be the more fusible of the two. The difference of melting-point should, however, not be too great. The melted glaze should rather, by penetrating into the already softened paste or by a chemical action upon its surface, form a more or less uniform mass with it. In cooling, the contraction of the glaze should follow that of the subjacent paste. This is a most important point; any discordance may lead to splitting, cracking, and ‘crazing.’ The beauty of the surface of porcelain depends on the fact that the glaze has become intimately united with the paste during the long exposure of both to a high temperature. We should not be conscious, in regarding a fine specimen of porcelain, of a greater or less thickness of glass covering an opaque substance; we should rather see in it the polished surface of ivory or of some precious marble.