Richard Selfridge on thu 31 jan 02
Bruce Girrell wrote
"And there is the problem. The annealing point of commercially available
fused silica products ranges from about 1000 =B0C to 1220 =B0C. So even with=
the
purest, most hydroxyl-free fused silica, we're barely at ^6 before hitting
the annealing point. The engineers with whom I spoke said that in high
temperature applications the observation ports are usually cooled with a
stream of lower temperature air moving past the glass to keep the window
below the annealing point."
I have 5 windows in our "Coffin" Kiln which are made from Neo Ceram which
I got locally from Crystal glass. They are about 4" x 5" and the same
pinkish colour which Bruce described. I put them in because I wanted to see
when I was reaching red heat. They cover the holes which were first
designed to function as peep holes with plugs. I had some bad experiences
with dunting 28" plates when I pulled the plugs and let in cold air in
earlier firings.
This glass and one called Pyro Ceram are rated at 1250 C which is fine in
my application as the window is on the outside of the kiln with 9" of hard
fire brick and 4" of adobe type insulation forming the "tunnel" to where
the actual fire is. They are slightly inset in the adobe insulation and
mortered with sairset. I can touch them when the cones are a flat cone 11
with my bare finger but they are too hot to leave your finger on. I have
only fired with them once but so far I am quite satisfied (no dunted
plates). I don't have pictures of them on our site but the kiln is well
documented there.
Regards, Richard Selfridge
http://www.selfridgeceramicart.ca=20
=20
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