Up: Glassmaking
Gilbert: 46 of 65
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and to make the glass uniform on both sides of the joint. Do this
as follows: Heat one third of the joint in the blowpipe flame
(Fig. 73), and when red hot blow a slight bulge.
FIG. 74
JOINING TUBES OF DIFFERENT
SIZES
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Now turn the joint one
third, heat the next third red hot and blow a slight bulge. Repeat
with the remaining third.
Now heat the first third again until it is red
hot and shrinks, then blow a slight bulge again. Repeat this with the
other two thirds.
Repeat this whole operation a third time and
blow just enough to leave the joint the same size as the remainder of
the tube or a little larger.
FIG. 75
MAKING A LARGE HOLE
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The heating and blowing has worked the joint
back and forth until the glass is fairly uniform. It makes a strong
joint.
Cut off the closed end and smooth the edge.
Repeat with a piece of No. 4 tube.
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