Fusing Glass Catalogue Final - Flipbook - Page 31
Wissmach Glass Firing Suggestions
Segment or
Step
1
Initial Heat Cycle
Rate (DPH)* Temperature
(Speed)
(Destination)
600°F
222°C
1000°F
538°C
Soak or
Hold in
Minutes
:10
Reasoning
Do not ask HOW, ask WHY and bypass
generic firing Schedules!
Be efficient and heat uniformly to avoid
thermal shock
In an initial first fuse firing, where all the glass starts out with layers of 3 mm glass, you can go up
between 900°F (482°C) and 600°F (222°C) per hour. The speed depends also on the size of glass.
Anything under 12” (30 cm) can be easily heated at the rate of 900°F (482°C) and bigger than 12” (30
cm) you can slow it down to 600°F (222°C) per hour.
Let’s assume you have already fused a blank and now want to fuse it again, or kiln form it on a
mold, you should slow down the initial heat cycle - and depending on size of the piece you can go up
450°F (232°C) and 300°F (148°C) per hour. Re-firing a cast glass piece of 3/4” (2 cm) thickness I do
not go slower than 200°F (93°C).
Holding it for 10 minutes at 1000°F (538°C) is sufficient to avoid thermal shock before you advance to
the Pre Rapid Heat.
2
Pre-Rapid Heat
Soak
AFAP***
1210°F
651°C
:15
Optional. No more worries about thermo
shock, just equalize temperatures and
minimize bubbles.
3
Rapid Heat to
Process Temp.
AFAP***
1410°F **
765°C **
:12
Going up fast will avoid devitrification and
increases efficiency. Choose the right
Process Temperature and Avoid overfiring
In this part of the firing, you decide about your final result and adjust the Time and Temperature for the
process like tack fuse, full fuse, slump drape, casting, combing …. Lower temperatures and longer hold
times usually will give you better results. Avoid over firing and undesired results, like kiln wash sticking to
glass and shifts in color and transparency, bursting bubbles and even shifts in compatibility.
There is a relation between hold time and temperature. You can full fuse glass by holding it for several
hours at 1250°F (676°C). So, holding it at any stage for an extended amount of time can change
4
the desired results and are unnecessary and inefficient.
Rapid Cool to
AFAP***
900°F
:45
Anneal Soak
482°C
Rapidly go through the devitrification zone.
Equalize internal glass temperature before
going through the annealing zone.
During the anneal soak we have to equalize the glass to the point where top middle and bottom have
no more than 10°F (5°C) difference in temperature. This is the minimum requirement, before the glass
keeps cooling through the Strain Point.
5
Anneal Cool
100°F
38°C
700°F
371°C
:1
Once you are passed the strain point the
glass will not anneal any more.
The actual range for the strain point in glass is between 800°F and 880°F. Taking the glass slowly through
700°F is playing it safe.
6
Final Cool Down
Natural
Rate
90°F
32°C
Leave the kiln closed to avoid thermal
shock.
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31
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