Nils Lou on tue 22 jun 10
an interesting aspect of heating and cooling clay is that
it seems to have a memory of the rate of heating and can be=3D20
safely cooled at the same rate. for example, if I fire to
1200C in three hours I can cool to room temperature in three
hours. match the curve of cooling to the curve of heating and
dunting is unlikely. industry does this every day, firing in as little =3D
as
45 minutes and cooling in 45 minutes.
nils lou, professor of art
http://nilslou.blogspot.com
www.tinyurl.com/bpc5nm
503.883.2274
"Play is the essence of creativity", and
"What is not brought forward into consciousness....
we later call Fate", Carl Jung
Taylor Hendrix on tue 22 jun 10
Now that is interesting. I wonder how far one can take this.
Taylor, in Rockport TX
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On Tue, Jun 22, 2010 at 9:12 AM, Nils Lou wrote:
> an interesting aspect of heating and cooling clay is that
> it seems to have a memory of the rate of heating and can be
> safely cooled at the same rate. for example, if I fire to
> 1200C in three hours I can cool to room temperature in three
> hours. match the curve of cooling to the curve of heating and
> dunting is unlikely. industry does this every day, firing in as little as
> 45 minutes and cooling in 45 minutes.
>
> nils lou, professor of art
> http://nilslou.blogspot.com
> www.tinyurl.com/bpc5nm
> 503.883.2274
> "Play is the essence of creativity", and
> "What is not brought forward into consciousness....
> we later call Fate", Carl Jung
>
douglas fur on tue 22 jun 10
Nils Lou
"an interesting aspect of heating and cooling clay is that
it seems to have a memory of the rate of heating and can be
safely cooled at the same rate. "
OK perfesser 'splain that one to us...
What do you think is the reason be hind this- There's less time to develop =
a
glassy phase and therefore less trouble caused by it in cooling?
DRB
Seola Creek
ivor and olive lewis on wed 23 jun 10
Dear Douglas and Nils Lou,
A few years ago there were articles in "Interceram" relating to firing of
porcelain types of clay with rapid heating and cooling cycles.
One of the things introduced during the cooling cycle was a precautionary
"Dwell Period". This prevented rapid cooling through the known temperature
at which Beta Quartz altered to Alpha Quartz.
A second point of interest is noted by Michael Cardew (p 38) During heatin=
g
Kaolin decomposes and one of the products is amorphous silica. This changes
to Crisatobalite above 1100 deg C (2012 F ) but the process is slow.
Furthermore, as has been pointed out by Ron Roy, clay bodies that are
compounded with Potash Felspar as an ingredient have, when molten, a
capacity to dissolve free silica, preventing the formation of cristobalite
and creating a greater volume of glass which does not suffer from Phase
Changes as it cools. Acicular Mullite, formed when Kaolinite is decomposed
also adds strength to the fused ceramic fabric.
Other clayart members may disagree.
Best regards,
Ivor Lewis,
REDHILL,
South Australia
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