Bottle-Moulds.—Moulds are made of various substances, in various forms, and are the subject of a considerable number of patents. The material of a mould must be durable, and must impart a good surface to the heated glass. Brass, cast-iron, and wet wood, are the materials most commonly employed. Metallic• moulds, while being worked, require to be kept nearly at a red-heat. Without this precaution, the surface of the glass is "ruffled" Care, on the other hand, must be taken, that the moulds are not so bet as to cause the glass to adhere. A small aperture must be left in the lower part of every mould, to allow the imprisoned air to escape while the hot glass is being introduced.
In order to form the neck of a bottle, moulds must be made in at least two, and usually in three pieces. Fig. 789 shows the simplest form of bottle-mould in use, in which the two sides are hinged together at the base. The chief objection to this mould is the fact that, where the two sides of the mould join, a seam in the glass is always formed. This seam is not noticeable when the bottles are square, and the join of the mould is at two angles of the bottle. Moulds in three pieces are made up of one piece for the body, and two for the neck, which are hinged above the shoulder. The seam down the body is thus avoided, although two slight seams are observable in the neck. Bottles made in these moulds can never be perfectly cylindrical, as the upper part of the body of the mould must always be slightly larger than the lower, to allow of the delivery of the bottle. The mould is closed by a treadle, acting upon two levers with inside springs, which re-open the mould when the foot is removed. A patent has lately been secured for giving a rotatory motion to the body of a mould, whilst being worked, in order to remove the seam in the glass at the point of junction of the two sides. Fig. 790 is a vertical section, and Fig. 791 a side eleva tion, of a bottle-mould hinged at the bottom ; Fig. 792 is a vertical section, and Fig. 793 a side elevation, of a bottle-mould hinged at the shoulder, with apparatus for giving the mould a partial rotation whilst the bottle is being blown. For this purpose, the folding sides A, which are opened and closed by the treadle B, instead of being hinged to the stationary bars of the mould, are hinged to a casing C. A second treadle D, pressed upwards by a spring d, is connected with the casing C. The "blower," closing the mould by pressure of his heel on B, can, by an up-and-down movement of his foot on D, cause a partial rotation of the whole mould around its base, or can cause the upper and lower parts to turn a little to and fro in opposite directions.
Pressed-Glass,—The application of machinery to the manu facture of glass, and the consequent partial substitution of me chanical for manual labour, has produced a ware suitable for almost every domestic purpose, and so cheap as to be within the reach of all classes. In the process of moulding glass, the molten mass is forced to take the form of the mould, both on its inner and outer surface, by the pressure of the glass-blower's breath ; in pressing glass, the molten glass takes the form of the mould, upon its outer surface, under the pres sure of a metallic plunger, driven by mechanical means, whilst the form of the inner surface is fashioned accord ing to the shape of the plunger. Pressed - glass always requires to be polished by the remelting of an outer film, roughened by contact with the metallic surface of the mould. The roughness is probably caused by the comparative coldness of the mould, which produces shrinkage and irregularity upon the surface of the hot glass. It is found that the hotter the mould can be kept, the smoother and brighter is the surface of the glass. Hand pressure can be applied to the production of small articles, by attaching a rubber or plunger by hinges to the mould, so that the hinges may form the fulcrum, and the resultant pressure may be obtained between.the fulcrum and the handle attached to the plunger.
For work on a large scale, pressure is usually applied by a weighted lever, or a screw and fly wheel. In the former, Fig. 794, the mould is placed at M ; a sufficiency of molten glass is gathered from the crucible by means of an iron rod, and dropped into the mould, being severed from the rod by aid of a pair of large shears. By depressing the handle H, which turns upon a fixed axis F, motion is communicated to the rod P, through the elbow. By this means, the frame B, sliding over the uprights I, together with the plunger P, is lowered. The lever 11 is restored to its original position by the counterpoise W. Fig. 795 represents a By turning the W, which is rigidly connected with the screw IS (working in the fixed cross bar 0), the plunger P is lowered, together with the rods R, and the bar V, sliding over the fixed uprights I.