ginny bivaletz on wed 30 aug 00
in a recipe for a ^ 10 glaze calling for 15% calcined
kaolin and 10% epk, could i just use 25% epk. most of
the catalogs i have don't even list calcined kaolin
and i was wondering if i should expect much of a
difference. thanks
=====
ginny from orcas island, washington.
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GURUSHAKTI@AOL.COM on thu 31 aug 00
You may get crawling using all that clay on a bisqued pot. You can calcine
clay yourself. Just put it in a bisqued bowl and fire up to around 1600
degrees Fahrenheit. The glaze would work fine without calcining if you're raw
glazing.
Regards,
June
Paul Taylor on thu 31 aug 00
Dear Ginney
The usual reason for using calcined clay of any sort, especially if the
glaze has a high viscosity, is to prevent crawling . Even a runny glaze can
still be viscose and gather in crawled lumps rather than sticking to the pot
.
Your glaze looks like a high alumina one - a bit viscose.
If you calcine the clay you sinter some of the finer particles together.
This cuts down on the water a glaze holds in suspension (In the bucket )
preventing the shrinkage of the glaze as it dries, and also the glaze has a
more powdery texture which also may prevent it cracking on the pot.
Any way. These cracks are very small and only obvious if you glaze
thickly. Even so they make fault lines for a viscous glaze to crawl away
from.
Another reason for calcining clay, china clay especially, is to prevent
crazing. The calcined china clay (Kaolin) is fired very high, and for a
long time, creating mullite crystals and getting rid of crystobalite and
Quarts. This material heats up and cools down more evenly no nasty
crystobalite - a form of quarts avoided by stone ware potters.
In this part of the world this high temperature calcined china clay is
called Molochite. It comes in different mesh sizes,and you will have to buy
it. For a glaze 200 is the largest particle size. White ware makers use the
courser stuff as a grog so be specific if you order it or an equivalent. If
your material supplier does not know what I am on about try one that does.
If you are testing try ordinary china clay first I suggest a grelog or an
equivalent a low titanium sort and put the smallest drop of sodium silicate
in the glaze just enough deflocculate the glaze so you have to put less
water in the glaze slop (the stuff in the bucket you dip into). Mix up a
small test.
If your body has a higher thermal expansion (shrinks more cooling down)
than the body the recipe was designed for you may get away without the
crazing.
If the china clay was calcined to fit on the body better before firing you
can calcine your own. Just fire the powder to bisk. It helps if you can give
the calcined clay a bit of a grind but sieve it dry through a fine sieve 200
is best. Remember to look after the lungs by wearing a mask.
Chances are the calcined clay stops both crawling and crazing I would get
some Molochite and leave mucking about with calcining china clays to
cheapskates and purists'.
And for beginners it is best if you follow recipes as near as possible
there is enough to go wrong with out taking extra chances.
-- Regards Paul Taylor.
Westport Pottery, Liscarney, County Mayo. Ireland.
http://www.anu.ie/westportpottery/
> From: ginny bivaletz
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 30 Aug 2000 19:34:51 -0700
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: calcined kaolin
>
> in a recipe for a ^ 10 glaze calling for 15% calcined
> kaolin and 10% epk, could i just use 25% epk. most of
> the catalogs i have don't even list calcined kaolin
> and i was wondering if i should expect much of a
> difference. thanks
>
> =====
> ginny from orcas island, washington.
>
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Mail - Free email you can access from anywhere!
> http://mail.yahoo.com/
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> ______________________________________________________________________________
> 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.
Craig Martell on thu 31 aug 00
Ginny axed:
> in a recipe for a ^ 10 glaze calling for 15% calcined
>kaolin and 10% epk, could i just use 25% epk. most of
>the catalogs i have don't even list calcined kaolin
>and i was wondering if i should expect much of a
>difference.
Hi:
If the glaze calls for 15% calcined kaolin and you add raw kaolin you will
be getting less alumina and silica in the glaze than is called for in the
recipe. Calcining removes OH (hydroxyls) and H2O. This accounts for Loss
on Ignition which is around 13% for most Kaolins. So, gram for gram you
get more Al2O3 and SiO2 from calcined kaolin.
You can calcine kaolin easily in an electric kiln. Just put the clay in a
bisque fired bowl. It's good if the bowl is fairly stout. Then fire to
about 1112F. I usually calcine kaolins to cone 06 but you can go
lower. Just be certain that the clay goes above 1112F which is the point
where the hydroxyls and bound water are lost. This is called "ceramic change".
When the kiln cools off you can remove the calcined kaolin and add it to
your glaze.
There are some calcined kaolins on the market but they are mainly used as
grog or fillers in clay bodies. They are not of the quality that you'd
want to use in a glaze. At least the ones I've seen. Most folks just do
their own. You can then choose the kaolin that you want instead of using
what's available.
later, Craig Martell in Oregon
Louis H.. Katz on thu 31 aug 00
Hi Ginny
The calcined kaolin is probably use to control some of the shrinkage of the drying
glaze. Replacing it may couse crawling of flaking of the glaze. Then again maybe
it wouldn't. Some companys do carry calcined kaolin, but you are probably just as
well off to make it yourself. Put some in an old pice of bisque ware and fire it
to cone 015 or so. It is hard on the bisque ware so don't expect to clean it out
and glaze it afterward.
Louis
ginny bivaletz wrote:
> in a recipe for a ^ 10 glaze calling for 15% calcined
> kaolin and 10% epk, could i just use 25% epk. most of
> the catalogs i have don't even list calcined kaolin
> and i was wondering if i should expect much of a
> difference. thanks
>
> =====
> ginny from orcas island, washington.
>
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Mail - Free email you can access from anywhere!
> http://mail.yahoo.com/
>
> ______________________________________________________________________________
> 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.
--
Louis Katz
NEW EMAIL ADDRESS Louis.Katz@mail.tamucc.edu
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Lorraine Pierce on fri 1 sep 00
Ginny, years ago I was taught to calcine my clays in an iron skillet on the
kitchen stove...just dry them out...worked for me. Of course you can put a
bowl of the clay you need calcined in your bisque kiln also, then grind it
up a bit with a mortar and pestle.Hope this helps. Lori in New Port Richey
Fl.
Craig Martell on fri 1 sep 00
Lori sedd:
>Ginny, years ago I was taught to calcine my clays in an iron skillet on the
>kitchen stove...just dry them out...worked for me. Of course you can put a
>bowl of the clay you need calcined in your bisque kiln also, then grind it
>up a bit with a mortar and pestle.
Hi:
It would be great if you could calcine clays while you were cooking
breakfast. It would save a lot of time but unfortunately a stove top
burner won't reach 1112F. That would be nice here in the winter because
you could heat part of the house too. The idea of calcining is to heat the
clay beyond the point where the hydoxyls and bound water are lost. Then,
when rewetted, the clay is totally non plastic. If you added water to the
stove top stuff after it cooled down, you'd still have plastic clay.
If you are having to regrind calcined clays after calcining or "dead
burning" them in a kiln, you are firing them too hot. I calcine clays all
the time and never have to gind them. The clays are just added to slips
and glazes and screened with the rest of the materials.
later, Craig Martell in Oregon
Lorraine Pierce on fri 1 sep 00
Thanks Craig...just goes to show you can't believe everything you were
taught...even back in the good old days! Lori in New Port Richey,Fl
John Weber on sat 2 sep 00
Calcined kaolin is just pure Kaolin that has been fired to bisque. So, if
you just put some kaolin in a previously fired bowl to bisque temperature or
above (no glaze) and bisque it again, you will have calcined kaolin.
Otherwise if you use the kaolin having not been calcined, like 25% in your
example, you change the expansion and your glaze or slip may not fit your
clay.
Wade Blocker on tue 22 may 01
Charley,
Put some clay into an unglazed bowl, or a bowl that has been bisque
fired, and put it in with your bisque firing. That should do the trick. You
can also purchase calcined clay from your ceramic supplier. Mia in ABQ
Farrero, Charley on tue 22 may 01
What temperature or Cone should Kaolin be taken to in order to obtain
"calcined Kaolin" as required in some glazes or slips.
Thanks
Charley Farrero
farrero@siast.sk.ca
Ceramics dept. WOODLAND CAMPUS
BOX 3003- PRINCE ALBERT.SK.
S6V 6G1 CANADA
ph:(306) 9537064 fax:(306) 9537099
http://www.siast.sk.ca/~woodland/dos/community/ceramic/
studio: Box 145 Meacham S0K 2V0 306-3762221
cfjj@sk.sympatico.ca
http://www.saskterra.sk.ca/profile.htm
http://www3.sk.sympatico.ca/handwave/hcharley.html
Paul Lewing on tue 22 may 01
Farrero, Charley wrote:
>
> What temperature or Cone should Kaolin be taken to in order to obtain
> "calcined Kaolin" as required in some glazes or slips.
Most people calcine to the same temperature they bisque to, just because
it's the most convenient. In reality, you only need to get the stuff
above red heat. I do a lot of china paint firing at cone 016, and it
works just fine for calcining stuff.
Paul Lewing, Seattle,
off tomorrow for the first backpack trip of the year, three days by Lake
Chelan in Eastern Washington, and it looks like the weather is going to
be great.
Chris Schafale on sat 10 dec 05
Kaolin can be calcined simply by including a bowlful in your next bisque
firing. It is used because a glaze with 40% raw kaolin is quite likely to
develop shrinkage cracks as the glaze dries on the pot. Depending on how
bad the cracking is, the glaze may either crawl or peel right off the pot
and end up on your kiln shelves. Calcining some of the kaolin reduces the
shrinkage and the associated risks of crawling. You don't want to calcine
all of it, though, because the raw kaolin helps keep the glaze from
settling in the bucket.
Chris
At 01:12 PM 12/11/2005, you wrote:
>The following recipe calls for calcined kaolin. How is kaolin calcined and
>is this really necessary or could regular kaolin be used. Glaze posted by
>Alicia Clausen 6-7-05.
>
>Dry Yellow Pumpkin
>
>18 frit 3134
>19 dolomite
>24 kaolin
>16 calcined kaolin
>16 spodumene
>8 flint
>ADD
>6 rutile
>14 titanium dioxide
>
>Thanks for the help.
>
>Brad Carter
>Grass Valley, Calif
>
>______________________________________________________________________________
>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.
Brad Carter on sun 11 dec 05
The following recipe calls for calcined kaolin. How is kaolin calcined and
is this really necessary or could regular kaolin be used. Glaze posted by
Alicia Clausen 6-7-05.
Dry Yellow Pumpkin
18 frit 3134
19 dolomite
24 kaolin
16 calcined kaolin
16 spodumene
8 flint
ADD
6 rutile
14 titanium dioxide
Thanks for the help.
Brad Carter
Grass Valley, Calif
Taylor from Rockport on sun 11 dec 05
Hey Brad:
Calcined kaoline is kaoline that has been low fired to drive off the
chemical water without also vitrifying it. The only reason I know for doing
this is to prevent the kaoline from adding to the drying shrinkage of the
raw glaze. I calcine my kaoline in a bisqued pot in my 04 bisque kiln. You
need to be really careful when transfering calcined kaoline in and out of
its storage container. It is especially nasty to the lungs.
You can certainly use regular kaoline but the weight will be different due
to H20 loss. Check the literature. Also, shrinkage may be a problem after
application. Bummer.
Calcining is an important concept for potters and other clay artists to
understand. It's practical application can solve many problems in the
studio. Another clayarter makes up his decorating slips by mixing identical
raw and calcined versions of his slip recipies to allow for application on
wet, cheese hard, bone dry and bisque pieces. Pretty cool, huh?
Have fun.
Taylor, in Rocport TX
On Sun, 11 Dec 2005 13:12:23 EST, Brad Carter wrote:
>The following recipe calls for calcined kaolin. How is kaolin calcined and
>is this really necessary or could regular kaolin be used.
Paul Lewing on sun 11 dec 05
on 12/11/05 10:12 AM, Brad Carter at BRADCARTER@AOL.COM wrote:
> The following recipe calls for calcined kaolin. How is kaolin calcined and
> is this really necessary or could regular kaolin be used. Glaze posted by
> Alicia Clausen 6-7-05.
>
> Dry Yellow Pumpkin
>
> 18 frit 3134
> 19 dolomite
> 24 kaolin
> 16 calcined kaolin
> 16 spodumene
> 8 flint
> ADD
> 6 rutile
> 14 titanium dioxide
Brad you don't say what temperature this is for, but since its one of
Alisa's I'll assume it's cone 6.
That's a HUGE amount of kaolin for a cone 6 glaze. I'm pretty certain if
some of it were not calcined, it would crawl.
To calcine clay, put some dry powder in a bowl and fire it to any
temperature between red heat and the temperature at which it starts to fuse.
Most potters just run kaolin through their bisque firings. I do it in a
china paint firing at cone 016. The temperature is not critical.
Paul Lewing, Seattle
ilene mahler on mon 12 dec 05
Please e-mail me off line Ilene....imahler@comcast.net...Thanks
----- Original Message -----
From: "Chris Schafale"
To:
Sent: Saturday, December 10, 2005 4:28 PM
Subject: Re: calcined kaolin
> Kaolin can be calcined simply by including a bowlful in your next bisque
> firing. It is used because a glaze with 40% raw kaolin is quite likely to
> develop shrinkage cracks as the glaze dries on the pot. Depending on how
> bad the cracking is, the glaze may either crawl or peel right off the pot
> and end up on your kiln shelves. Calcining some of the kaolin reduces the
> shrinkage and the associated risks of crawling. You don't want to calcine
> all of it, though, because the raw kaolin helps keep the glaze from
> settling in the bucket.
>
> Chris
>
> At 01:12 PM 12/11/2005, you wrote:
>>The following recipe calls for calcined kaolin. How is kaolin calcined
>>and
>>is this really necessary or could regular kaolin be used. Glaze posted
>>by
>>Alicia Clausen 6-7-05.
>>
>>Dry Yellow Pumpkin
>>
>>18 frit 3134
>>19 dolomite
>>24 kaolin
>>16 calcined kaolin
>>16 spodumene
>>8 flint
>>ADD
>>6 rutile
>>14 titanium dioxide
>>
>>Thanks for the help.
>>
>>Brad Carter
>>Grass Valley, Calif
>>
>>______________________________________________________________________________
>>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.
>
> ______________________________________________________________________________
> 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.
Snail Scott on tue 13 dec 05
At 01:12 PM 12/11/2005 EST, you wrote:
>The following recipe calls for calcined kaolin. How is kaolin calcined and
>is this really necessary or could regular kaolin be used...
Using calcined clays reduced the shrinkage of the
dry glaze on the surface of the clay, allowing the
recipe to contain more clay than could normally be
applied to bisque.
It's no big deal to calcine your own. Just put some
kaolin in a bowl and fire it your next bisque load.
It doesn't have to go that hot, but it will work OK
and it's convenient.
-Snail
Ron Roy on fri 16 dec 05
This may be an underfired glaze at cone 6 - the alumina is very high. The
SiO2 is very low so it is not a stable glaze.
RR
>The following recipe calls for calcined kaolin. How is kaolin calcined and
>is this really necessary or could regular kaolin be used. Glaze posted by
>Alicia Clausen 6-7-05.
>
>Dry Yellow Pumpkin
>
>18 frit 3134
>19 dolomite
>24 kaolin
>16 calcined kaolin
>16 spodumene
>8 flint
>ADD
>6 rutile
>14 titanium dioxide
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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