Doug Gray on tue 13 nov 01
"Could it be that the extra heat in the kiln walls helps to delay the
cooling of a material which has had sufficient time for all of the
chemicals and minerals to dissolve and react?"
Ivor,
I think you are right. I have another side note that would support your
theory. I fire a large updraft kiln, large by my standards anyway,
approximately 150 cubic feet of actual stacking space. The actual
chamber is two soft brick layers thick with and additional insulation on
the exterior. The kiln is fired with 20 natural draft venturi burners
which come through the floor of the kiln. The firing schedule is
simple, candle over night to about 1300 degrees Fahrenheit, then to cone
10 (or 11) within about 12 hours, with body reduction at cone 010 and
slight reduction maintained until cones are down. There are three small
flues in the arch, none any wider than a standard brick and only two spy
holes in the door. So when we shut down, the kiln is shut up fairly
tightly, although I don't specifically try to cover each of the burner
ports. The kiln cools slowly. Our cooling cycle, in spite of my
impatience, has been lengthened to three days. But as has been
mentioned on clayart before, we do get good glaze development and
color.
As a closeted and responsible pyromaniac (if that doesn't sound too
extreme) I would be the first to encourage you to get as hot as you'd
like.
doug
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