rohde on wed 31 oct 01
can some one help me out=20
what is Calcined Kaolin
David Beumee on wed 31 oct 01
Calcined kaolin has been purified by the action of heat. Kaolin is
alumina and silica and water, and by calcining kaolin you remove both
surface and chemically combined water, rendering the clay non-plastic.
Spreading a layer of a kaolin in a bisque bowl or platter, then heating the
kiln to 1300 degrees F is a really good way to calcine kaolin, because that
amount of heat does the job without allowing any of the clay to begin to
sinter(the first stage of melting). This means you can likely add the
calcined clay directly to a clay or glaze without first having to grind it
and screen it. If it is a deep layer of kaolin, say six inches of clay, it
is a good idea to hold the temperature at 1300 F for half an hour.
David Beumee
Earth Alchemy Pottery
----- Original Message -----
From: "rohde"
To:
Sent: Wednesday, October 31, 2001 8:24 PM
Subject: help with what is calcined kaolin... what is the sub for it.
can some one help me out
what is Calcined Kaolin
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miriam shelomith on thu 1 nov 01
This is the answer that I received...and understood(!)when I asked the same
question... Hope you find it as clear as I did... Pottermim
>From: "Fay & Ralph Loewenthal"
>
>Subject: Calcined
>Date: Tue, 30 Oct 2001 09:28:14 +0200
>
>
>Dear Miriam, if you calcine a substance, then you are
>driving off all the water. That is the natural water and
>the chemically bonded water molecules within the
>substance. Different substances have correspondingly
>different temperatures that one has to fire the substance
>to, to drive off the water. I calcine Zinc Oxide, to use in
>crystaline glazes, in a bisque firing at about 950 C.
>Hope this helps from Ralph in Cape Town.
>PS Colemanite is notorious for spitting all over the kiln.
>This is because of the chemically bonded water. It is
>recommended to calcine colemanite before using in a
>glaze.
>From: rohde
>
>
>can some one help me out
>
>what is Calcined Kaolin
>
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Christena Schafale on thu 1 nov 01
Calcined kaolin is just kaolin that has been "pre-fired", usually to about
bisque temperature. What this does is to reduce the wet-to-dry shrinkage
that takes place after you apply a glaze to your pot. Glazes with lots and
lots of kaolin often have such high shrinkage that they crack and can fall
off the pot as they dry, and/or cause crawling when fired even if they
don't actually fall off. Therefore, you substitute calcined kaolin for
part of the raw kaolin in the recipe, which reduces the shrinkage. You can
make your own calcined kaolin just by putting some EPK or other kaolin in a
bisqued bowl and putting it in with your regular bisque firing. Do be sure
that you are wearing a mask when you handle this stuff, however, as it is
more "fluffy" than raw kaolin and gets into the air very easily (been
there, done that).
If for some reason you don't care about shrinkage, or you don't feel like
messing with calcining your own, and you want to take the chance that the
recipe will work fine with raw clay, you would sub 1.15 grams of raw kaolin
for every 1 gram of calcined kaolin in your recipe (this is because the
calcined has "lost weight" through loss on ignition during the
prefiring). Going the other direction, subbing calcined for raw, you would
put in .87 grams of calcined for every 1 gram of raw.
Chris "calcined kaolin is my friend" Schafale
At 09:24 PM 10/31/01 -0600, you wrote:
>can some one help me out
>
>what is Calcined Kaolin
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
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>settings from http://www.ceramics.org/clayart/
>
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>melpots@pclink.com.
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Ababi on thu 1 nov 01
In an old book I read was written to calcine clay in any glaze when it
comes to more than 30% because of it's high shrinkage, means this glaze
has 42% clay, I use 30 raw 12 calcined. You can try it yourself with
wet ball clay make a slurry like glaze and deep or paint like it was a
glaze. As soon as it dries there will be many cracks.
Only in one case when I wanted these cracks I used it deliberately un
calcined.
In one of the PMI magazines article about crystalline glaze they
explain it. In that article they calcine the cobalt too, but this is a
crystalline glaze and you don't need to do it.
When you make an engob or slip for bisque you are called to use calcine
Kaolin, again to avoid too much shrinkage and peeling off while drying.
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
sharon@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
---------- Original Message ----------
>This is the answer that I received...and understood(!)when I asked the
>same
>question... Hope you find it as clear as I did... Pottermim
>>From: "Fay & Ralph Loewenthal"
>>
>>Subject: Calcined
>>Date: Tue, 30 Oct 2001 09:28:14 +0200
>>
>>
>>Dear Miriam, if you calcine a substance, then you are
>>driving off all the water. That is the natural water and
>>the chemically bonded water molecules within the
>>substance. Different substances have correspondingly
>>different temperatures that one has to fire the substance
>>to, to drive off the water. I calcine Zinc Oxide, to use in
>>crystaline glazes, in a bisque firing at about 950 C.
>>Hope this helps from Ralph in Cape Town.
>>PS Colemanite is notorious for spitting all over the kiln.
>>This is because of the chemically bonded water. It is
>>recommended to calcine colemanite before using in a
>>glaze.
>>From: rohde
>>
>>
>>can some one help me out
>>
>>what is Calcined Kaolin
>>
>_________________________________________________________________
>Get your FREE download of MSN Explorer at
>http://explorer.msn.com/intl.asp
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>______
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>You may look at the archives for the list or change your subscription
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>melpots@pclink.com.
Christena Schafale on thu 1 nov 01
I calcine clay in my regular cone 07 bisque firings, and I have never
needed to grind/screen the resulting material.
Chris
>
>Spreading a layer of a kaolin in a bisque bowl or platter, then heating the
>kiln to 1300 degrees F is a really good way to calcine kaolin, because that
>amount of heat does the job without allowing any of the clay to begin to
>sinter(the first stage of melting). This means you can likely add the
>calcined clay directly to a clay or glaze without first having to grind it
>and screen it. If it is a deep layer of kaolin, say six inches of clay, it
>is a good idea to hold the temperature at 1300 F for half an hour.
>
>David Beumee
>
>Earth Alchemy Pottery
Cindy Strnad on thu 1 nov 01
Dear Rohde,
Calcined kaolin is powdered kaolin which has been
fired. The reason for using it is that, in a
recipe high in kaolin, you may have trouble with
the glaze shrinking too much. This causes the
glaze to crack when drying and, upon firing, to
crawl (separate along the crack lines).
Place the quantity of kaolin you'd like to calcine
in a bisqued bowl and fire it along with a load of
bisqueware. If your recipe calls for calcined
kaolin, just weigh it out and dump it in. If not,
you'll have to take into consideration the fact
that calcined kaolin weighs less than a
corresponding amount of raw kaolin. Weigh it
before firing and after to figure the difference.
Or just fire the amount you're planning to use.
Best wishes,
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
Ilene Mahler on thu 1 nov 01
kaolin that has been bisqued..Ilene in Conn
rohde wrote:
>
> can some one help me out
>
> what is Calcined Kaolin
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
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Wade Blocker on thu 1 nov 01
To calcine means to heat a ceramic material to the temperature necessary to
drive out the chemical water and other volatile materials.
If you do not have calcined kaolin just put some kaolin into an unglazed
dish and fire it with your next bisque firing. Mia in balmy ABQ
Steve Mills on fri 2 nov 01
Literally biscuit fired China Clay (Kaolin). Coarser grades are often
called Molochite and used in place of Grog in white clays.
Steve
Bath
UK
In message , rohde writes
>can some one help me out=3D20
>
>what is Calcined Kaolin
--
Steve Mills
Bath
UK
Ababi on sat 29 nov 03
In an old book I read was written to calcine clay in any glaze when it
comes to more than 30% because of it's high shrinkage, means this glaze
has 42% clay, I use 30 raw 12 calcined. You can try it yourself with
wet ball clay make a slurry like glaze and deep or paint like it was a
glaze. As soon as it dries there will be many cracks.
Only in one case when I wanted these cracks I used it deliberately un
calcined.
In one of the PMI magazines article about crystalline glaze they
explain it. In that article they calcine the cobalt too, but this is a
crystalline glaze and you don't need to do it.
When you make an engob or slip for bisque you are called to use calcine
Kaolin, again to avoid too much shrinkage and peeling off while drying.
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
sharon@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
---------- Original Message ----------
>This is the answer that I received...and understood(!)when I asked the
>same
>question... Hope you find it as clear as I did... Pottermim
>>From: "Fay & Ralph Loewenthal"
>>
>>Subject: Calcined
>>Date: Tue, 30 Oct 2001 09:28:14 +0200
>>
>>
>>Dear Miriam, if you calcine a substance, then you are
>>driving off all the water. That is the natural water and
>>the chemically bonded water molecules within the
>>substance. Different substances have correspondingly
>>different temperatures that one has to fire the substance
>>to, to drive off the water. I calcine Zinc Oxide, to use in
>>crystaline glazes, in a bisque firing at about 950 C.
>>Hope this helps from Ralph in Cape Town.
>>PS Colemanite is notorious for spitting all over the kiln.
>>This is because of the chemically bonded water. It is
>>recommended to calcine colemanite before using in a
>>glaze.
>>From: rohde
>>
>>
>>can some one help me out
>>
>>what is Calcined Kaolin
>>
>_________________________________________________________________
>Get your FREE download of MSN Explorer at
>http://explorer.msn.com/intl.asp
>________________________________________________________________________
>______
>Send postings to clayart@lsv.ceramics.org
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
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