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How It Is Made
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towards the exit, and so in the course of a few hours a bottle passes through the tunnel.
    Window or sheet glass making is entirely blowing work. The workman collects about 25 lbs. of glass on the end of his tube, and works the mass into a cylindrical shape on a hollow "marvering" block.
Cylinder blown from bulb
Fig. 55
He then blows and spins it simultaneously till it expands into a flattened ball (Fig. 55), 12 inches to 18 inches in diameter. The next step is to draw out the bottom half of the ball into a long cylinder of the same diameter. This is done by heating the glass at a circular hole in a special furnace, and swinging it through part of a circle over and in a long, deep pit, at the edge of which the workman stands. After several reheatings a closed cylinder from 4 feet to 7 feet long, according to the skill of the workman, is obtained. The cylinder is then burst open by blowing it full of air and heating the end, which gives way in the centre under the pressure of the expanding air inside. Further heating and rapid twisting of the blowpipe "flushes out" the end in line with the rest of the cylinder.