The first of these, one more especially of archæological interest, would include all the glass made before the discovery of the process of forming a vesicle by blowing through a hollow tube. Nearly all the glass that finds its way into our collections would be classed in the second period; this would extend from the beginning of our era to the end of the eighteenth century. In the course of these long centuries, the work of the glass-maker has of course been influenced by the varying schools and fashions of different ages and countries, but technically there is no great advance to be noted in the work of the seventeenth and eighteenth centuries when compared with that of the early days of the Roman Empire; and this is still more true if we consider merely the materials employed, their preparation, and the methods of their fusion. But before the end of the eighteenth century a great change had set in. The manufacture of glass in England and France had become an important industry, and we enter upon the third or industrial period. With the general advance in mechanical processes that is so characteristic of the time, the old methods of the working of glass were swept aside, so that before the middle of the last century, whatever of interest was to be found in the manufacture and in its results depended upon anything rather than upon the artistic qualities of the glass made. Now, as I have said, the characteristic and dominant quality of glass is to be found in its capability of being blown into vessels of varying shape when in a viscous and semi-fluid state. All glass then, made at a time when advantage had not yet been taken of that essential property of the material, we may class together in a primitive group. This line of demarcation is as important, to return to a comparison I have already made, as that between hand-moulded pottery and that thrown on the potter’s wheel. The objects made in the earlier period by primitive processes were mostly small, and their merit depended chiefly upon the brilliancy and the skilful juxtaposition of a few simple colours—they may for the most part be classed as _verroterie_.