iandol on sun 1 sep 02
Dear Mary Lynch,=20
A lot of discussion about this sort of thing recently on Clayart.
There are three systems to consider when thinking about cracking a kiln =
at such a high temperature to hasten cooling of the objects within.
Kiln refractories. Since there will be a higher temperature within the =
body of the refractory they may deteriorate due to phase changes. =
Contracting quickly on the outside can also impose stress which leads to =
breakage. IF brick, the outer surface may spall away and kiln debris can =
fall onto the pots. This may not happen until the kiln is reheated, then =
pots get covered in..."Kiln Shit"... If Fibre, the fibre may embrittle =
prematurely and break away. Think "Health hazard"
Kiln Furniture. Some forms of kiln furniture refractory do not take =
kindly to quenching. They also become brittle, may break and have to be =
replaced.
The Pottery. At 500 F, the interior of a pot, especially anything which =
is thick, will be much higher. Even if there are no phase changes the =
fact that the outer layer cools and contracts quickly imposes tensions =
which may be higher than the tensile strength of the glaze. So expect =
Crazing.
People make choices. If those people want to get their hands on their =
work because they are impatient and are prepared to accept the down =
sides, let them.
Regarding the development of the Matt Glazes. I do not think this would =
make any difference. If they are matt because not all of the materials =
dissolve in the molten glaze, they are there in full force all the time =
so rapid cooling would make no difference. IF they are precipitation =
matts cause by saturating the glaze with something which will grow in =
the vitreous solution, this must happen generally throughout the glaze =
before it passes down through the Glass transition temperature, say =
about 1300=B0F. I would be interested in the source of their information =
on this.
Best regards,
Ivor Lewis
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