Mercy Langford on thu 25 apr 02
I've worked with low fire clay for some time andd I'm trying my hand at
porcelain. My mom who is very good at low fire saays that why can't I fire
porcelain clay to high bisque (5 or 6) to mature and low fire glaze (o4) .
Itell her that although it aain't working for me so far you are supposed to
fire porcelain at (o4-06) range for bisque and then high or should I say
medium fire the glaze to(4-6). She says that cannot work and compares it to
your body can't be bigger than the dress. She tells me that the
body(greenware) has to be fired to higher temperature than the glaze or it
will expand,craze and everything else. Tell Me! Is Mother always Right? Any
input will be appreciated. Mercy
Snail Scott on thu 25 apr 02
At 11:34 AM 4/25/02 EDT, you wrote:
>...She tells me that the
>body(greenware) has to be fired to higher temperature than the glaze or it
>will expand,craze and everything else.
This is a low-fire concept. For low-fire,
there are many good reasons to bisque to
a higher temperature than the glaze firing,
including the tendency of the outgassing to
'kill' certain glaze colors unless fired to
a higher temperature before glazing. This
works mainly because low-fire clay is still
porous after that highest-temp firing, and
is easy to glaze because of that.
However, high-fire work will become vitrified
after firing to its maturation temperature,
nonabsorbent, and thus rather difficult to
glaze because of this. That is why high-
fire work is bisqued to about the same
temperatures as low-fire work, but is fired
to maturity during the glaze firing later.
You mother was right, but only with regard to
low-fire practices. For high-fire, you are
quite correct in your intention to bisque low
and then glaze-fire high. Go for it!
-Snail
Matt MacIntire on thu 25 apr 02
Your Mother thinks like an industrial ceramist, while you think like a =
studio potter.=20
My understanding is that many industrial porcelains are (bisque) fired =
to a high temperature and glaze fired with a thin application of a lower =
temperature glaze. This allows the ware to be packed densely on special =
stilts that only leave teeny glaze flaws. Meanwhile studio potters =
typically do the reverse. Potters are after different glaze effects and =
a different kind of interaction between the clay and the glaze.
Either way, all the shrinkage that occurs with the ware happens *before* =
the glaze itself has solidified. So it is possible to get glazes that =
fit either way. =20
Her analogy is a little weak. But keep her around anyway.
Matt
-----Original Message-----
From: Mercy Langford [mailto:JJLANGF@AOL.COM]
Sent: Thursday, April 25, 2002 11:35 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: A Glaze and Temperature Question
I've worked with low fire clay for some time andd I'm trying my hand at
porcelain. My mom who is very good at low fire saays that why can't I =
fire
porcelain clay to high bisque (5 or 6) to mature and low fire glaze (o4) =
.
Itell her that although it aain't working for me so far you are supposed =
to
fire porcelain at (o4-06) range for bisque and then high or should I say
medium fire the glaze to(4-6). She says that cannot work and compares =
it to
your body can't be bigger than the dress. She tells me that the
body(greenware) has to be fired to higher temperature than the glaze or =
it
will expand,craze and everything else. Tell Me! Is Mother always Right? =
Any
input will be appreciated. Mercy
_________________________________________________________________________=
_____
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.
Ababi on thu 25 apr 02
Hello Merci.
Porcelography is a matter of geography!
The real porcelain is fired to around 1300C to be beautiful and mature,
yet if you are "poor" in temperature you may compromise and make
similar behaving claybodies for lower temp/ cone. In Val Cushing's hand
book there are several such claybodies.
I will add here one I use,Val Cushing makes it with two kaolins I use
it with EPK or French kaolin
it is for 04 I fire it to 06 and raku.
40kaolin
20ball clay ( AK)
18 talc
12 alumina
10molochite
it is a raku claybody
As I wrote there are many more claybodies , buy the book make Val
Cushing happy and yourself too.
Here is a ^6 porcelain claybody prepared for me by Tom Buck.
I used it with un plastic kaolin I could buy from my supplier therefor
Tom opposed the place of the kaolin and the ball clay. These days I
make it with EPK.
Ababi's ^6 Porcelaneous by Tom Buck
===================================
BALL CLAY (AK)...... 48.00 47.06%
ENGLISH KAOLIN CC31. 33.00 32.35%
NEPHELINE SYENITE... 14.00 13.73%
ALUMINA HYDRATE..... 5.00 4.90%
BENTONITE........... 2.00 1.96%
========
102.00
CaO 0.04* 0.17%
MgO 0.37* 1.24%
K2O 0.27* 2.06%
Na2O 0.32* 1.65%
TiO2 0.01 0.09%
Al2O3 4.58 38.33%
SiO2 11.25 55.55%
Fe2O3 0.07 0.92%
Si:Al 2.46
SiB:Al 2.46
Expan 5.86
Another book is Behrens's book Glaze Projects.
From my short experience on the subject,I think it is easier to build a
claybody than a glaze, read these book and I tell you Mother is almost
always Right!
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
---------- Original Message ----------
>I've worked with low fire clay for some time andd I'm trying my hand at
>porcelain. My mom who is very good at low fire saays that why can't I
>fire
>porcelain clay to high bisque (5 or 6) to mature and low fire glaze
>(o4) .
>Itell her that although it aain't working for me so far you are
>supposed to
>fire porcelain at (o4-06) range for bisque and then high or should I say
>medium fire the glaze to(4-6). She says that cannot work and compares
>it to
>your body can't be bigger than the dress. She tells me that the
>body(greenware) has to be fired to higher temperature than the glaze or
>it
>will expand,craze and everything else. Tell Me! Is Mother always Right?
>Any
>input will be appreciated. Mercy
>________________________________________________________________________
>______
>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.
Hank Murrow on thu 25 apr 02
> Mercy wrote;
>
>I've worked with low fire clay for some time andd I'm trying my hand at
>porcelain. My mom who is very good at low fire saays that why can't I fire
>porcelain clay to high bisque (5 or 6) to mature and low fire glaze (o4) .
>Itell her that although it aain't working for me so far you are supposed to
>fire porcelain at (o4-06) range for bisque and then high or should I say
>medium fire the glaze to(4-6). She says that cannot work and compares it
to
>your body can't be bigger than the dress. She tells me that the
>body(greenware) has to be fired to higher temperature than the glaze or it
>will expand,craze and everything else. Tell Me! Is Mother always Right? Any
>input will be
>appreciated._______________________________________________________________
_______________
Dear Mercy;
Surely your mother must have some English genes in her, as
that is the way the English made their Bone Porcelain. Since the body
got so soft at elevated temps, they bisqued to high temp (C 8-11) and
glost (glaze) fired at a lower temp (C/04-C/5). That way, the wares
could be packed tightly in the high fire with no glaze on them, the
wares keeping each other straight....less warpage. Only downside is
that they nearly completely lost the fine body/glaze interface that
the oriental wares acheived. That is one of the reasons English bone
china needed so much decoration to liven up the surfaces. IMHO.
Anyway kiddo..........you do it however you like it! BTW, all
my porcelain is bisqued @C/07, and glazed in reduction or oxidation
to C/10+.
Cheers, Hank in Eugene
Marcia Selsor on thu 25 apr 02
Dear Mercy,
Your your is right in some respect in that if you bisque a low temp piece to
^06
and then put a ^04 majolica on it, it will craze.
She also knows that the procelain needs to be fired to maturity.
If you read Susan peterson's new book, Smashing Glazes, Tom Coleman bisques
his
porcelain to maturity ^6 and then puts some wild glazes on it at ^04. It is
the
teapot on the cover of the book. So your mother is right is some respects.
It is a
more common practice to bisques as you describe and glaze to the maturity of
the
clay..in this case ^6. In RR and JH book, Mastering Cone 6 Glazes, they
address
the crazing problem as well as much more..
Best wishes,
marcia in montana
Mercy Langford wrote:
> I've worked with low fire clay for some time andd I'm trying my hand at
> porcelain. My mom who is very good at low fire saays that why can't I fire
> porcelain clay to high bisque (5 or 6) to mature and low fire glaze (o4) .
> Itell her that although it aain't working for me so far you are supposed
to
> fire porcelain at (o4-06) range for bisque and then high or should I say
> medium fire the glaze to(4-6). She says that cannot work and compares it
to
> your body can't be bigger than the dress. She tells me that the
> body(greenware) has to be fired to higher temperature than the glaze or it
> will expand,craze and everything else. Tell Me! Is Mother always Right?
Any
> input will be appreciated. Mercy
>
>
____________________________________________________________________________
__
> 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.
Paul Lewing on thu 25 apr 02
Mercy, it can be done either way. Studio potters tend to bisque low and
fire high because it makes applying glazes so much easier. But the
dinnerware industry (when they don't once-fire) usually bisques high and
glazes lower. They do this because it's more economical to fire a tightly
packed bisque to the higher temperature and the more loosely packed glaze
load to a lower temperature. Also anything that's going to warp, crack, or
outgas does it before they invest in glaze and decoration.
Paul Lewing, Seattle
Jeff Tsai on thu 25 apr 02
I think this has been well covered by the other folks...I seem to find
myself
agreeing with Snail a lot, but I think he hit it on the head pretty well, as
did Ababi.
THe only thing I wish to quickly add is simply that your mother's comment
about glaze falling off and such is something ceramicists must deal with
regardless of what temperature they work at. almost every clay body shrinks
in firing, and glazes do to. Since we usually bisque high fire ware to
temperatures lower than the glaze firing temperature, we consider how the
clay will shrink during the glaze firing and try to adjust the shrinkage of
the glaze so it will work on the clay's final shrinkage.
Basically, that's what Ron Roy lectured about during his 30 minute
presentation at NCECA: Glaze fit and stability. Always test your glazes as
each clay body shrinks differently, but bisquing to cone 6 probably won't
make your life much easier.
-jeff
vince pitelka on fri 26 apr 02
> This is a low-fire concept. For low-fire,
> there are many good reasons to bisque to
> a higher temperature than the glaze firing,
Snail -
This is common practice at low-fire, but it is by no means a low-fore
concept. High-bisque low-glaze is very common in the china industry, where
the wares are initially high-fired either bare or with a clear glaze, and
then are low-fired for color and then often ultra-low-fired for enamels or
lusters.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Mercy Langford on fri 26 apr 02
Thanks for the information-Mercy
Snail Scott on sat 27 apr 02
At 10:56 PM 4/26/02 -0500, you wrote:
>Snail -
>This is common practice at low-fire, but it is by no means a low-fore
>concept. High-bisque low-glaze is very common in the china industry...
Yes, I know. The post was asking for confirmation
(or not) of advice offered by a 'low-fire expert',
though, so I stuck to commenting on low-fire
practices. The high-bisque methods of china
manufacturers just didn't seem relevant to the
question, since relatively few craft potters find
an advantage to it. For every standard method of
claywork, I'd bet that someone somewhere is getting
good results doing just the opposite, but I didn't
want to confuse the issue for a newcomer to the
craft. I never meant to imply that high-fire bisque
is never done; only that it is not the norm in
studio pottery.
-Snail
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