The general principles of glass-blowing are :—(l) a hollow bulb at the end of a blow-pipe will collapse under the pressure of the atmosphere, unless it be continually blown into; (2) a bulb blown while the blow-pipe is raised will have a flattened form ; (3) one blown whilst the blow-pipe paints downwards will be elongated ; (4) a hollow bulb or a solid mass, allowed to hang downwards, and swung from side to side, will be greatly elongated ; (5) if a bulb be not continuously rotated, it will become distorted ; (6) hollow or solid masses of viscid glass may be almost indefinitely elongated by traction.
The Course of manufacture is :—(l) The blowing-iron is heated at the end, and a sufficient weight of molten glass is collected upon it ; (2) the glass is blown and fashioned with the tools, and may be decorated with knobs or threads, with coloured casings, with gold, platinum, or powdered glass, with iridescence or with frosting ; (3) the fashioned vessel is placed in the annealing-oven ; (4) the vessel is removed from the annealing-oven, and probably requires to be flattened at its base by means of the cutters' wheel. If it be a bottle, it may require to be stop pered. The other processes to which the annealed vessel may be subjected, and which will be briefly described, are—cutting, engraving, carving, engraving by acid, and roughening by the sand-blast process.
In Fig. 775, a b c, &c., represent the different stages in the manufacture of a light wine-glass : (a) the molten glass has been gathered upon the end of the blow-pipe, and has been consolidated by rolling upon the iron slab or marver ; (b) the solid mass has been slightly marked by the com pression of the knife-blades of the spring tool; the knob thus formed is polled out by the same tool to form the leg ; (c) the upper part of the mass is expanded by the breath to farm the bowl ; (d) the leg is gradually formed ; the small button remaining at the end is removed by a sharp blow ; (e f) a small quantity of glass has in the meanwhile been gathered, blown into, and compressed, as shown at f, to farm the foot ; the bowl and leg are pressed against the doubly indented hollow bulb f, and made to adhere to it ; the bulb f is severed from the blow-pipe, upon which it was gathered, by the application of a moistened tool ; (g) the bulb, which is now attached to the leg of the wiue-glass, is divided by the spring tool at the point of indentation ; (h) the open cup which remains is flattened, partly by the insertion of the points of the spring tool, partly by centrifugal force generated by rapid rotation ; to the bottom of the flattened foot, a light solid working-rod (k) is affixed by a seal of glass, and the bowl (i) is severed from the blow-pipe by the application of a moistened tool ; (1) the rough edge is sheared and smoothed by melting at the mouth of the crucible. The finished wine-glass is separated from the working-iron by a sharp blow, and is
carried by a boy to the annealing-oven.
The seal of glass, by which the working-iron was fixed to the bottom of the foot, leaves a rough mark, which has to be polished away by the glass-cutter, after the wine-glass has been annealed. To avoid the necessity of this extra proocse, a tool has been lately used to a considerable extent, which clips and holds the foot of the wine-glass by means of a spring. This tool, represented in section in Fig. 776, takes the place of the solid working-iron. By depressing the outer coating a of the tool upon the spring 8, space is left between o d for the admission of the foot of the wine glass. The spring s, as soon as pressure is re moved, presses the foot of the wine-glass, which rests upon a, against the stationary plate c. In Fig. 775, a bode represent the work of the " servitor " or first assistant ; f g h k, the work of the footmakor or second assistant; and I, tho work of the workman. In making heavier wine glasses, the bowl is blown first, and a piece of molten glass is dropped on to its base to form the leg. The stages of manufacture are shown in Fig. 777.
A patent has lately been scoured by Richard son, of Hodgetts and Richardson, for a tool for fashioning the feet of wine-glasses. This con sists of two plates of wood or carbon hinged together, with straps for regulating the extent of the opening, and for opening the two plates. The workman's right hand compresses the soft metal of the foot between the plates, whilst his left hand rotates tho wine-glass attached to the end of the blow-pipe. By means of this tool, a foot is formed from a solid mass of glass, and the operation requires but little skill. The feat thus formed are oven and smooth, but inferior to blown feet in lightness. The same Inventor has produoed a machine for shaping the bottom and sides of heavy tumblers. The tumbler is blown, ronghly fashioned in the ordinary way, and, while still attached to the blow-pipe, is pressed against a flat disc of iron (the size of the bottom of the tumbler), from which, iron fingers project upwards, and surround the body of the tumbler. The 775.