Up: Glassmaking
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.
Fig. 55
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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.
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