Now it happens that for us this restriction is in every way convenient. For though the material basis is the same, it is evident that both the artist who works in mosaic and the designer of stained windows are concerned, each in his department, with artistic problems only incidentally connected with the material in which they work. In other words, the art element in both these crafts only becomes prominent at a stage when the actual preparation of the glass is completed. It is, however, certainly a pity that there is no English word which would not only clearly connote the class of objects with which I have here to deal, but which would at the same time distinctly comprise nothing beyond. I have now explained the somewhat restricted and artificial sense of the word glass that I propose to accept in this work. But for a moment let us pass to the other extreme, and going beyond the ordinary connotation of the term include in it the glazes of pottery—the word ‘glaze’ is in its origin the same as glass—as well as the many forms of enamel. In all these cases we are dealing with substances of similar composition. They may all probably be traced back to a common origin, so that from an evolutionary point of view we have here an instance of the development of the complex and varied from the simple and single. Looking at the question in another way, the art of the enameller, using the term in a restricted sense, may be held to be subsidiary both to that of the potter and of the glass-worker; while many of the problems that arise in treating of the glazes of fictile wares—questions as to fusibility, or as to the colours employed and the changes of these colours during the firing—turn up again in the manufacture of glass. We shall see that experience gained in following the processes of one art may serve to throw light upon the difficulties and problems of the other. Historically the connection between glass and pottery is not so close. In some degree the prevalence of one art has tended to oust the other, or to relegate it to an inferior position. The Greeks, who carried the potter’s art to such perfection, knew little about glass—it was long an exotic substance for them. The Romans, on the other hand, who in the first centuries of our era first fully appreciated and developed the capacities of glass, produced little pottery of artistic interest. In the sixteenth century, in Umbria and Tuscany, where the finest majolica was made, we hear nothing of the manufacture of glass, while on the other hand the fayence of Venice, at this time pre-occupied with her glass, was of subsidiary importance. If we turn to the home of porcelain, in China glass has always held a subordinate position, while in Japan it was until recent days practically unknown.