Up: Glassmaking
Gilbert: 7 of 65
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Experiment 3. To make the edges smooth.
Hold one end of the six-inch piece of No. 2
in the tip of the flame (Fig. 8), and turn constantly until it is
FIG. 8
MAKING THE EDGES SMOOTH
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just red hot. Take it out and let it cool on the blocks. Do you
find that the edges are smooth?
Repeat with the other end.
Repeat with both ends of the six-inch piece
of No. 4.
If thick glass is heated quickly it may
crack, because the hot exterior expands more quickly than the
cooler interior and produces internal strains.
FIG. 9
THE BLOWPIPE FLAME
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The No. 6 tube is comparatively thick and
should be heated gradually as follows: Hold the end in the
flame for 1 second, then withdraw it for about 1 second; hold it
in the flame again for 1 second, and withdraw it for 1 second.
Repeat this eight or ten times, then hold and turn it in the flame
until red hot.
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