Crown- and Sket-Glass .lfanufacture.—The following details of this branch of glass-making have been most obligingly communicated by Chance Bros. & Co., who are by far the largest manufacturers of crown- and sheet-glass in this country. Fig. 759 is a plan of a crown-glass manufaotory :—F is the oblong furnace, containing six crucibles c ; x, openings in the walls of the furnace, through which the molten glass is gathered ; w, auxiliary furnaces, or " nose-holes "; s, brickwork screens, to protect the workmen from the intense heat of the furnaces ; k, anneal ing-kilns. Fig. 760 is a side elevation of a crown-glass furnace :—X, the open ings already referred to ; y, small re cesses, in which the ends of the blow pipes are heated, preparatory to gather ing glass from the crucibles. Fig. 761 —A, section of a blow-pipe, measuring about 6 ft. in length ; B, a solid iron working-rod or " ponty." Fig. 762 shows the stages of manufacture from the solid mass to the flattened disc.
Upon the surface of the melted glass, is a ring of fire-clay, which, when the materials were thrown in, lay at the bottom of the pot, and after the completion of the melting, found its way upwards. This ring, floating in the centre of the pot, prevents the exterior surface of the melted glass, which becomes stiff and stringy during the long period of working, from mingling with the interior or hotter surface, which thus remains throughout of a euitable consistency. The labour of the skimmer, whose duty it is to clear the surface from any scum or dirt that may collect upon it, is considerably dimin ished by the ring, which, limit ing the space from which the glass is drawn, limits also the apace to be cleansed, and any bubbles or impurities in the glass have a tendency to attach them selves to the ring.
The melted glass having been brought, by the gradual cooling of the furnace, from a state of complete fluidity to a workable consistence, the gatherer dips the end of his pipe, or hollow rod of iron, into the pot within the ring, and, twirling it round its axis to equalize the thickness of the gathering, he collects upon the end, or " nose," as it is technically called, a pear-shaped lump of glass. Resting his pipe upon a stand or horse, he turns it gently round, and allows the surface of the lump to cool, to fit it for a second gathering.
The lump completed, the gatherer cools his pipe under a trough of water, that he may bundle it at any point, and proceeds to roll the glass upon a " marver," or metallic bed, until it assumes a conical form, the apex of the cone forming the "bullion-point." A boy now blows down the pipe while it is still being turned by the gatherer on the marver, and expands the glass into a small globe. Having been heated, it is blown again, and assumes the shape of a Florence flask, and the future rim of the developed plate is prepared by rolling the piece, near the pipe-nose, upon the edge of a marver. Again heated, it is expanded by the blower into a large globe. During this expansion, it is important to keep the bullion-point exactly in the position which it previously occupied, in a line with the axis of the pipe. To effect this, the blower rests
his pipe upon the iron support, and while he blows down the pipe and turns it round at the same time, a boy holds against the bullion-point a piece of iron terminating in a small cup. Again presented to the fire, by the peculiar manipulation of the workman, and the peculiar direction of the flame upon it, the front of the globe is flattened, the possibility of the globe collapsing during this operation being prevented by its rapid revolution round its axis. The piece now resembles in shape an enormous decanter, with a flat bottom and a very short neck. The bullion point is still to be seen in the centre of the flat bottom, and its use.now becomes manifest. The pipe is laid horizontally upon an iron rest, and a man approaches, having in his hand a ponty, tipped with a lump of molten glass. Pressing this lump upon an iron point, so as to give it the form of a little cup, he fits it, when thus shaped, onto the bullion-point, to which it soon becomes firmly attached. The lump thus formed is called the "bull's-eye" or " bullion " of the developed plate. The incision of a piece of cold iron in the glass round the nose of the pipe, and a smart blow, soon detaches the pipe, which, after having lain a few minutes, till the glass adhering to it has cracked off, is warmed, and carried back to the pot to repeat its course.
The end of the piece, whicb was next the now detached pipe, is called the nose, and gives it name to the furnace or nose-hole, Fig. 763, where this nose is, on account of its thick ness, heated almost to melting, with a view to the coming operation. A man, with a veil before his face, stands in front of a circle of flame, into which he thrusts his piece of glass, meanwhile rapidly revolving his ponty. The action of heat and centrifugal force combined' makes the nose of the piece expand, the parts around cannot resist the ten dency, the opening grows larger and larger, and finally there appears a thin transparent circular plate of glass. Still whirling, the "table," as it is now called, is carried off, laid flat upon a support called a "whimsey," detached by shears from the ponty, lifted upon a fork into the annealing-kiln, and placed upon its edge against the preceding table. The weight of so many tables pressing one against another would cause the hindermost to bend, were this not prevented by the intervention of iron frames or " dressers," which divide the tables into sets, the first dresser leaning against the wall of the kiln, the second against the first, and so on. As the bull's-eye or centre lump, which the ponty has left, keeps each table from close contact with its neigh bours, the air passes freely between them, and the annealing is accomplished with tolerable rapidity, varying from 24 to 48 hours, according to the number of tables in the kiln. From the kiln, the tables are conveyed to the warehouse, having passed, since their first exit from the pot, through the hands of ten distinct workmen.