Royal Institution of Great Britain · The Making of a Sheet of Glass · Page 10

    The pipe is then carried on a carriage running on rails with the swing-hole underneath down which he swings the cylinder to elongate it. A hole is made in the end by adding a blob of molten glass and cutting it off by means of secateurs. By further heating and rotating an open ended cylinder is created. The cylinder is now deposited on a frame and the blow pipe end is removed by a sharp tap. The end of the cylinder is then removed by means of a thread of molten glass wrapped around it. The thread of glass causes intense local heating, and a sudden chilling of the heated spot by natural means causes the end of the cylinder to drop off.
    The cylinder is next examined for faults, and is then split or cut by running a diamond cut on the inside of the cylinder, and at a selected point, into two or more sections, which are then flattened out on the bed of a gas-fired kiln.
    DRAWN CYLINDER. The blown cylinder process was replaced by an American one introduced to this country in 1909, in which the cylinders are drawn and blown mechanically. Larger masses of molten glass are involved and much larger cylinders can be made. The glass is taken from the working end of the tank in a ladle. The curtains of glass on the sides of the ladle are removed and the molten glass poured into a red hot two-sided crucible which is mounted over a kiln heated by gas. Then the flanged blow pipe is lowered into the glass and the glass wells up into the flange. The pipe with its cylinder of glass is slowly drawn up while air supplied to the interior maintains the cylinder at a uniform diameter. (Figure 3.) Speed and air supply are automatically controlled to ensure this.