The essential feature of the process of glass pressing consists, as already indicated, in forcing a layer of glass into contact with a mould by the pressure of a mechanically actuated plunger. For this purpose a suitable mould and plunger as well as a press for holding the former and actuating the latter are required. The moulds are generally made of a special quality of close-grained cast-iron, and they are kept trimmed and dressed in much the same manner as the moulds used for blowing (except that the latter are sometimes made of wood). For the purpose of facilitating the removal of the finished article, the moulds are generally made in several pieces which fit into one another and can be separated by means of hinges. A very important point about these moulds is that the various pieces should fit accurately into one another, since otherwise a minute “fin” of glass will be forced into every interstice, and the traces of these fins will always remain visible on the finished article; the very perfect fit required to entirely prevent the formation of such fins is, of course, scarcely attainable in practice except in the case of new moulds, so that the traces of fins are generally to be found on all pressed articles, and serve as a ready means of identifying these products when an attempt is made to imitate better classes of glass-ware by their means. The presses used in this process are generally of the hand-lever type; power presses could no doubt be used, but it is contended that the hand-press has a very great advantage in allowing the operator to judge by touch when sufficient pressure has been exerted, and this is an important consideration, since an excessive pressure would either force the glass out of the mould altogether or would be liable to burst or injure the mould seriously. The actual presses consist of vertical guides and levers for controlling the movement of the plunger and a table for holding the moulds, and in some cases a system of cranks and levers for opening and closing the moulds. The process of pressing is exceedingly simple. The proper quantity of glass is gathered from the pot on a solid rod and dropped into the mould. The thread of glass which remains between the glass in the mould and that remaining on the iron is cut off with a pair of shears, and then the plunger is lowered into the mould and allowed to remain there until the glass has stiffened sufficiently to retain its shape, when the plunger is withdrawn. In this proceeding it will be seen that the glass is forced into intimate contact with the relatively cold surfaces of mould and plunger, and while undergoing this treatment the glass must remain sufficiently plastic to readily adapt itself to the configuration of the mould. It is therefore not surprising to find that the pressing process can only be used successfully with glass of a kind specially adapted for it. Certain varieties of flint glass and some barium