vince pitelka on sun 7 jul 02
> Okay, now I am confused. One correspondent writes to put the plaster bat
into the
> kiln. Another writes to never do this. Which is it?
John -
Never do it. Even on low heat in a kiln it is excessive for any plaster
form. When fresh-cast plaster gets around 180 degrees it starts to
disintegrate. Best way to dry plaster is in a warm, low-humidity
atmosphere. It is possible to fire certain plaster mixes, as they do in
traditional investment casting for bronze, aluminum, etc., but there is no
reason in the world to do that with any plaster form to be used in the
ceramic studio.
Best Wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@worldnet.att.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
John Vandermeulen on sun 7 jul 02
Okay, now I am confused. One correspondent writes to put the plaster bat into the
kiln. Another writes to never do this. Which is it?
John V
Carol Ross wrote:
> Yikes! I would NEVER put plaster in a kiln! It can be heated carefully in a
> regular oven if it's necessary, but the temp shouldn't exceed 170F degrees.
>
> Carol
> doodles@mac.com
>
> > > > >
> > > > > >
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Snail Scott on mon 8 jul 02
At 09:26 PM 7/7/02 -0500, Vince wrote:
It is possible to fire certain plaster mixes, as they do in
>traditional investment casting for bronze, aluminum, etc...
Just to add to Vince's observation:
Those plaster investments for metal casting are
'waste molds'. They disintegrate after use. In
fact, since the plaster has at that point been
re-calcined, dipping in water will cause it to
dissolve, conveniently removing the investment
from the cast material.
A technique (like 'firing' plaster) may be a
good one for some applications, and not for
others. It's a rare process that can't be modified
for other purposes, utilizing the 'defect' of one
usage to be an asset for another. That's part of
the reason why simple answers often appear to
contradict each other.
-Snail
Bobbruch1@AOL.COM on tue 9 jul 02
I missed the original post on this subject, but one way to dry freshly poured
plaster bats or molds is with a dehumidifier.
<<<<From: vince pitelka
Subject: Re: Plaster/kiln
>>> Okay, now I am confused. One correspondent writes to put the plaster bat
into the kiln. Another writes to never do this. Which is it?
<<plaster form. When fresh-cast plaster gets around 180 degrees it starts to
disintegrate. Best way to dry plaster is in a warm, low-humidity atmosphere.
It is possible to fire certain plaster mixes, as they do in traditional
investment casting for bronze, aluminum, etc., but there is no reason in the
world to do that with any plaster form to be used in the ceramic studio.
- Vince
Snail Scott on fri 12 jul 02
At 10:59 AM 7/7/02 -0300, you wrote:
>Okay, now I am confused. One correspondent writes to put the plaster bat
into the
>kiln. Another writes to never do this. Which is it?
>John V
If plaster is overheated, it will re re-calcined,=20
and turn back into its chemically-active form.
If you want it to stay solid, don't get it too=20
hot. =20
(This is why 'lime pop' is usually a delayed=20
phenomenon - the plaster in the clay is fine=20
while it stays dry after firing, but when=20
atmospheric humidity or washing moistens it,=20
look out!)
You can heat plaster to speed the drying process,
but keep it under 150=BA or so, for a safety margin.
-Snail
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