glasses are used for this purpose, but the greater quantity of pressed glass, particularly as produced on the Continent, is made of a lime-alkali silicate containing considerable quantities of both soda and potash and relatively little lime; while sufficiently resistant for most purposes, this glass is particularly soft and adaptable while in the viscous condition. The deleterious effect produced upon glass surfaces when brought into contact with relatively cold metal has already been referred to above, and it only remains to add that this is the principal difficulty with which the glass-pressing process has to contend. It is overcome to some extent by the aid of the reheating process described above; but this is only a partial remedy, and in the majority of pressed glass products the surface is “covered” as far as possible by the application of relief decorations such as grooves, spirals, and ribbings. An attempt is sometimes made to imitate the appearance of cut glass, but the rounding of the angles during the reheating process destroys the sharpness of the effect and allows of the ready detection of the imitation, while the cheapness of the decoration when applied in the mould has frequently led manufacturers to grossly over-decorate, and, therefore, destroy all claim to beauty in their wares. CHAPTER IX. ROLLED OR PLATE-GLASS. In the present chapter we propose to deal with all those processes of glass manufacture in which the first stage consists in converting the glass into a slab or plate by some process of rolling. We have already considered the general character of the rolling process, and have seen that, although hot, viscous glass lends itself readily to being rolled into sheets or slabs, these cannot be turned out with a smooth, flat surface. In practice the surface of rolled glass is always more or less dimmed by contact with the minute irregularities of table or roller, and larger irregularities of the surface arise from the buckling that occurs at a great many places in the sheet. These limitations govern the varieties of glass that can be produced by processes that involve rolling, and have led to the somewhat curious result that both the cheapest and roughest, as well as the best and most expensive kinds of flat glass, are produced by rolling processes. Ordinary rough “rolled plate,” such as that used in the skylights of workshops and of railway stations, is the extreme on the one hand, while polished plate-glass represents the other end of the scale. The apparent paradox is, however, solved when it is noted that in the production of polished plate-glass the character of the surface of the glass as it leaves the rollers is of very minor importance, since it is entirely obliterated by the subsequent processes of grinding, smoothing, and polishing. Intermediate between the rough “rolled” and the “polished” plate-glass we have a variety of glasses in which the