A
slump point test is useful when you wish to determine the approximate
annealing point of an unknown glass. The methodology follows:
Prepare
a strip of the glass 305mm x 25mm. Suspend this strip above the
shelf on 25mm pieces of kiln furniture. Leave a 275mm span between
the kiln furniture. A piece of kiln furniture also needs to be
placed on top of the glass to keep it in place.
Fire
at 200C per hour to ca.
550C, then fire at 50C/hour to about 700C. Observe frequently from
600C. Record the temperature when the middle of span touches the
shelf. This is also the slumping temperature of the glass when fired this way.
Subtract
40C from the “touch down” temperature
for the approximate annealing point temperature.
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