PLATE GLASS has the same composition as sheet and crown glass, but is melted in vast open ves sels (sometimes holding 2% tons) resting upon frames behind fire-clay doors. After the long fusion is perfect the door is thrown open and the tank is seized by an immense fork mounted on a truck, and carried bodily to the casting-table, where it is hoisted by a crane and poured over the metal bed, which has a very smooth, highly polished surface. A heavy roller passes over it, spreading the glass out in a uniform thickness determined by the height of the strips on either side of the table. Instantly it is rolled into the annealing-oven for a tempering of several days. It conies out in the form of rough plate. To be polished it is fastened by plaster of Paris to'a large rotary platform which revolves so that the entire surface is covered at each rotation by the disks of grinding-machines which rub it with sand, then with emery, and last with rouge, first on one side, then on the other, till 40 per cent. of its thickness is removed, and it remains a shining sheet from one-quarter to three-eighths of an inch thick. 'Rolled plate' is cast upon an engraved table, which gives the impressions of fluted lines or fancy patterns in a translucent body of glass adapted to panels and partitions.
Guars GLAss, Or BOTTLE-GLASS, is the coarsest form, made from roughest materials, and is the simplest branch of glass-work. The bottle-blower gathers the molten glass on his blowpipe, in the quantity desired for his bottle, or jar, or demi john, puffs a bubble into it, drops the inflated lump into an iron mold, which is closed together over it by a small boy, and blows the glass into its permanent shape with the lettering or trade mark which was cut in the mold. The jagged mouth is then rounded in the 'glory-hole,' and the bottle goes to the 'leer.' Bottle-molds are made of brass or iron, and must be maintained at nearly a red heat while being used. The simplest form is of two sides hinged together at the base, and the familiar ridges running up each side of a glass bottle are formed where the two sides of the mold shut together. Sometimes the mold is in three pieces, one for the body and two for the neck, in which case the ridges are only on the neck; this is usually the case with wine-bottles. Formerly the blowing of bottles was done wholly by the breath; but recently machines for blowing fruit-jars and other wide-mouth jars have been successfully operated, and the process will doubt less be extended.