It may be inferred from these two sections that Theophilus probably regarded all the artistically coloured and enamelled vessels of his time as of Byzantine origin. He knows nothing about the constituents of the fusible enamels. The pseudo-Heraclius, on the other hand, has a chapter (viii.) telling how glass is made from lead (calcined previously to a powder) and how such glass is coloured. In another section the same writer refers to the ‘_plumbeum vitrum Judæum scilicet_,’ which is ground on a slab and used as an enamel to paint on glass. Most of the remaining sections of Theophilus’s second book are concerned with the preparation of coloured glass for windows, but the last of all, ‘_On Rings_,’[94] describes carefully a method of making articles of _verroterie_ with a small furnace and little crucibles. Lead is here mentioned casually as a constituent of the glass, and this, I think, is the only reference to this substance to be found in Theophilus’s chapter on glass. Here as elsewhere we may note that the word _sapphirus_ is used as the equivalent of a blue glass paste (coloured probably by cobalt), and that it is referred to as a material that is at hand already prepared. Such cakes or slabs appear to have been an article of commerce from a period of remote antiquity. Something not unlike them has been found in Babylonian excavations (p. 40). Similar cakes of coloured glass are still exported to China from the Bohemian glassworks. CHAPTER VIII GLASS OF THE LATER MIDDLE AGES IN WESTERN EUROPE One of the chief glories of the later Middle Ages in Western Europe is undoubtedly to be found in the stained glass windows of the churches. Theophilus early in the twelfth century had already made himself master of this art, which he regarded as essentially a French one. The preparation of these _vitraux_ involved a knowledge of the process either of spinning the molten _paraison_ or of opening out the cylinder of glass, both comparatively late developments of the art of glass-blowing. In the staining of the glass we know from extant specimens what splendid results were obtained.