MANIPULATION. The curious viscosity assumed by molten glass has already been referred to. While in this condition it may be gathered up in a soft mass on the end of a stick, and, if the stick be a tube, the lump may be distended, by blowing through the tube, into a hol low sphere. The form of this sphere or bulb may be modified by manipulating the pipe, and if a second iron be attached by a seal of glass to the other side of the bulb, it may be drawn out into a tube. If the bulb be opened by removing it from the blowing iron, and then, after attaching it at its opposite side to another iron, be trundled rapidly like a mop, the opening will expand, by centrifugal force, into a disk. These are the processes which, infinitely diversified and compli cated by the skill of the workmen and the na ture of the product, constitute the art of the glass-blower. Every melting-furnace has sev eral working furnaces called 'glory-holes,' where the glass-worker reheats his work. These are small blast-furnaces, each affording several open ings into the flames.
There are three general methods of shaping glass—by blowing, pressing, and casting.
WiNnow-GLAss is produced in a square or oblong furnace, and requires the most muscular and skillful workmen. The 'monkey pots' are filled with the mixed 'batch,' and when this is melted a second charge is shoveled in, followed, as soon as it flows, by a third and a small amount of 'millet' (broken glass), which fills the pots. Sixteen hours are consumed in the entire melting, and the master-melter carefully watches his `monkeys,' forcing the furnaces to their highest heat. As soon as the signs appear indicating that the molten glass or 'metal' is ready to work, the heat is lowered to thicken the glass for the blowers. Each man is trained to one small part of the whole process, and does nothing else. The gatherer holds a mask before his face, by a plug grasped between his teeth, to screen him from the glare of the furnace, and starts the `journey' of the glass by dipping the blowpipe into the pot several times, dexterously forming on its end an oval mass of the white, hot, gummy `metal,' which weighs from 20 to 40 pounds, ac cording to the thickness and size of the sheet to be made. Revolving the ball in the glaring pot, he completes its symmetry and consistency, and then turns it in an iron mold till it takes a per fect pear shape. This finishes the gatherer's
work, and he hands the fiery sphere to the blower, who is the master-workman of the establishment. He takes the pipe from the gatherer's hand and blows a huge bubble of air into it, then another, and another, swelling the solid sphere into a great decanter, with its thinnest part hardening next the pipe, as one end of the cylinder which is to be evolved from the soft thick mass at tached to it. Now he takes his stand on the long narrow platform which leads to his furnace door over a deep pit, swinging the glowing bulb like a giant pendulum into the depths below, persuading it to elongate with frequent puffs at the most effective moments. Now and then, as it cools into hardness, he rests his pipe on a prop and softens the end in the furnace, or he may toss the cylinder above him until it settles into a workable condition. Thus he blows and swings, and heating from time to time the molten mass, he works it till it grows as long as himself and becomes a round-topped cylinder. When this has cooled considerably, he holds the end in the furnace, blows strongly into it, and, covering the mouthpiece with his thumb, an explosive re port is heard. The imprisoned air, heated ex pansively, has burst an opening through the soft extremity. Revolving the end rapidly in the fur nace, the blower enlarges the hole by centrifugal force, till it is as large as the diameter of the cylinder. Then he cools it in a pit to a cherry red, and his part is done. An assistant carries it off and detaches it from the blowpipe by en circling the neck with a thread of hot glass and then touching the line with a cold iron. The cylinder is then cracked lengthwise by a diamond, or by passing a red-hot iron inside it. Next the flattener takes it. First he warms the split cylinder, then places it on the stone before him, a fire-clay table, which revolves within an oven. The curved sheet opens in the heat like an uneven sheet of paper, and he smooths it by a wooden block. The stone carries it then to the cooling oven, whence it is lifted on an immense fork into a car at the mouth of the 'leer,' or annealing tunnel, and there it is tempered for service.