Kate Johnson on wed 13 oct 04
So, I'm getting confused here, with the information from Jon Pacini of
Laguna...he wrote "Officially Laguna recommends ^04 for bisque firing *all*
the clays we make. The reasoning being, with a hot bisque you increase the
strength of the ware and you have hopefully been able to burn out all the
nasties that cause such things as glaze pin holing. Yet this temperature
still allows the ware to be porous enough to accept a good coating of
glaze." That's my emphasis, of course...
Here's my question...I buy clay locally, and it gives a really broad range
of bisqueing temps on the box, depending on the clay body .
As I've mentioned, I fire things in the electric kiln at school, and have to
fit my stuff in around the kids' firing schedules. They use white
earthenware exclusively, which Metro Supply's box suggests bisquing at
^06-04. I'm using terra cotta, which the box says to bisque at. ^06-2.
Originally, I had mine fired WITH the kids' stuff, at the lower temps, but
discovered it feels stronger, less porous, and even rings if fired to ^2, so
now I'm really trying to wait till I have almost a kilnful of my own.
Is this really necessary? Would it be as good to bisque fire to, say ^04
with the kids' stuff, then glaze-fire a bit higher? We mostly use Duncan
commercial glazes, and it doesn't seem to me that they suggest glaze firing
very high--we're not talking ^6 stuff here, let alone ^9 and up.
I'm happy with my results as is, but it does get frustrating sometimes to
have to wait till the kiln is free.
Thank you!
(And by the way, the cracked flask was a bust, literally. Now officially A
Learning Experience...)
Best--
Kate
Cynthia Bracker on thu 14 oct 04
I tend to agree with Jon. Further, a hotter bisque is more important if
you're doing low-fire. For Earthenware, I would use an 03 cone in the
sitter (or program an 03) which should net you about an 04 throughout
your kiln. Then for the glaze firing you can lower the temperature a
little if you wish and use an 04 or 05. (Although personally, if you
have a kiln sitter kiln, just use the same 03 cones and push it a little
closer to the thin side of the cone. You'll get a slightly cooler
firing that way and your Duncan glazes should turn out very well there)
As to your local clay, I'm making an assumption here, but I think when
you say "Metro Supply" you are referring to KC Metro, who uses the same
clay we do (Flint Hills) the temperatures listed on the box are an
overall maturing range for the listed bodies, not a bisque
recommendation. Terra Cotta is indeed beautiful at Cone 2, turning a
darker brownish red rather than the "flower pot" red that it is at 05.
You can certainly still bisque it with the kids work, then use
underglazes to decorate and glaze fire to Cone 2. The tricky part is
finding a clear glaze at Cone 2. I don't know of one available
commercially. You'll probably have to find a recipe for one and mix it
up yourself.
I hope this helps!
Cindy Bracker
Bracker's Good Earth Clays, Inc.
Kate Johnson wrote:
> So, I'm getting confused here, with the information from Jon Pacini of
> Laguna...he wrote "Officially Laguna recommends ^04 for bisque firing
> *all*
> the clays we make. The reasoning being, with a hot bisque you increase
> the
> strength of the ware and you have hopefully been able to burn out all the
> nasties that cause such things as glaze pin holing. Yet this temperature
> still allows the ware to be porous enough to accept a good coating of
> glaze." That's my emphasis, of course...
>
> Here's my question...I buy clay locally, and it gives a really broad
> range
> of bisqueing temps on the box, depending on the clay body .
>
> As I've mentioned, I fire things in the electric kiln at school, and
> have to
> fit my stuff in around the kids' firing schedules. They use white
> earthenware exclusively, which Metro Supply's box suggests bisquing at
> ^06-04. I'm using terra cotta, which the box says to bisque at. ^06-2.
> Originally, I had mine fired WITH the kids' stuff, at the lower temps,
> but
> discovered it feels stronger, less porous, and even rings if fired to
> ^2, so
> now I'm really trying to wait till I have almost a kilnful of my own.
>
> Is this really necessary? Would it be as good to bisque fire to, say ^04
> with the kids' stuff, then glaze-fire a bit higher? We mostly use Duncan
> commercial glazes, and it doesn't seem to me that they suggest glaze
> firing
> very high--we're not talking ^6 stuff here, let alone ^9 and up.
>
> I'm happy with my results as is, but it does get frustrating sometimes to
> have to wait till the kiln is free.
>
> Thank you!
>
> (And by the way, the cracked flask was a bust, literally. Now
> officially A
> Learning Experience...)
>
> Best--
> Kate
>
> ______________________________________________________________________________
>
> 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 Clark on thu 14 oct 04
Kate, yes. You should have no problem with bisque firing your work
to 04 along with the kiddies. No need to wait. The glaze firing to a bit
higher, or lower temp, is the way to go. I don't think you need to be
concerned with vitrification issues with your clay body if that is what
you are thinking about. The vast majority of "earthenware" clay bodies
do not vitrify in the firing process anyway so you shouldn't have any
problem with glaze application at an 04.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Where we have FINALLY left the heat of summer behind!!!!!
Bruce Girrell on thu 14 oct 04
There seems to be a growing consensus that a higher bisque temperature
produces stronger, more crack resistant ware.
For at least some applications I *strongly disagree*.
My experience is that for raku and horsehair decoration, a higher bisque
temperature will lead to _more_ cracking in the glaze or decoration firing.
I tried all sorts of things to reduce our cracking losses during horsehair
decoration, which subjects the pots to far more thermal shock than raku, and
found that the one thing that reduced losses from cracking more than
anything else was using a lower bisque temperature.
In addition, I am surprised to see people recommending higher bisque
temperature to control glaze application. In cases where I have accidentally
overfired my bisque, I find that I can barely get a glaze layer to stick and
then it takes a very long time until the glaze layer has dried enough that
the pot can be handled or another glaze layer applied.
Bruce "low-temp bisque firers unite!" Girrell
Kate Johnson on thu 14 oct 04
Hi Cindy...
>I tend to agree with Jon. Further, a hotter bisque is more important if
> you're doing low-fire. For Earthenware, I would use an 03 cone in the
> sitter (or program an 03)
Yep, we use a Skutt automatic electric kiln...programmable...
Terra cotta is relatively low-fire, yes? And what's the difference between
Flint Hills' terra cotta and red earthenware? I thought they were the same
thing, according to some of my pottery books, but the box lists both...what
I'm using now is fairly groggy, which I like in some instances and in
others, not so much...
which should net you about an 04 throughout
> your kiln. Then for the glaze firing you can lower the temperature a
> little if you wish and use an 04 or 05. (Although personally, if you
> have a kiln sitter kiln, just use the same 03 cones and push it a little
> closer to the thin side of the cone. You'll get a slightly cooler
> firing that way and your Duncan glazes should turn out very well there)
I have no idea what he glaze fires to, but they seem to turn out well...
> As to your local clay, I'm making an assumption here, but I think when
> you say "Metro Supply" you are referring to KC Metro,
Yes, sorry, I always get the name wrong! And for some reason I thought you
were with them--I was hoping you'd answer.
who uses the same
> clay we do (Flint Hills) the temperatures listed on the box are an
> overall maturing range for the listed bodies, not a bisque
> recommendation. Terra Cotta is indeed beautiful at Cone 2, turning a
> darker brownish red rather than the "flower pot" red that it is at 05.
Here is where I am confused, again...hopefully my potter friend/teacher
won't be. "Overall maturing range" is a term I don't quite understand.
Does that mean you can fire up to that temp, shouldn't fire higher, bisque
or glaze firing...? Cumulative? Sorry, I am SUCH a dork when it comes to
the mechanics of this stuff, and numbers and I are virtual stramgers...
> You can certainly still bisque it with the kids work, then use
> underglazes to decorate and glaze fire to Cone 2. The tricky part is
> finding a clear glaze at Cone 2. I don't know of one available
> commercially. You'll probably have to find a recipe for one and mix it
> up yourself.
> I hope this helps!
Hmmm...yes, thank you--but sounds like I might be better off sticking to
what I'm doing now and developing a bit of patience with the firing
schedule. I like the nice deep red-brown and the higher vitrification
(can you refer to ^2 as vitrified? Feels less porous, anyway...)
Interestingly, even when I have the kiln all to myself, we get a variety of
reds and red-browns, no matter what the setting. Must be that uneven kiln
heat/stacking that we've been discussing.
> Cindy Bracker
> Bracker's Good Earth Clays, Inc.
So where are you? I'm in Excelsior Springs, MO...
Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm
Cynthia Bracker on thu 14 oct 04
1. Terra Cotta vs. Earthenware Red: There are 2 answers here. The
actual terms are more or less synonymous. Terra Cotta is Latin meaning
burnt earth. Answer number 2 (which is more to the point) is that in
the Flint Hills Brand, Terra Cotta has 18% grog whereas Earthenware Red
has no grog. Otherwise, they are essentially the same clay body.
2. KC Metro is a different company located in Kansas City, MO on 350
Highway. I am with Bracker's Good Earth Clays, located in Lawrence, KS
(loosely a suburb of Kansas City) Their business is a little more
geared toward hobby ceramics whereas we are more geared toward potters.
There is some cross-over on both sides, but it's generally friendly
competition.
3. "Overall Maturing Range" refers to the ultimate firing temperature
of the clay, or the temperature at which the clay performs "at its
best" If you look at the side of the box, there are 3 distinct
groupings of clay. In the bottom grouping, for instance, you will see a
clay body called "stoneware" and the range on it is 8-10. This means
the final firing should be in the range of Cone 8 to Cone 10. It is at
that point that the clay becomes "mature". Basically, all clays bisque
at the same temperature. The concept of a bisque firing is to
chemically change the clay. After the clay is bisqued, you can apply
decoration (glazes or underglazes or whatever) and then fire it to the
maturing temperature. Of course there is also single firing, but that's
a whole different discussion. I hope this helps a little. You're
welcome to call and discuss uneven firing, bisque temps, terms etc. with
me if you like. Our toll-free number is (888) 822-1982. Or you might
consider coming in. Excelsior Springs is not too far from Lawrence and
we've got some really good restaurants, a beautiful old-fashioned
downtown shopping district, great museums and galleries etc. down here too!
Cindy
Kate Johnson wrote:
> Hi Cindy...
>
>> I tend to agree with Jon. Further, a hotter bisque is more important if
>> you're doing low-fire. For Earthenware, I would use an 03 cone in the
>> sitter (or program an 03)
>
>
> Yep, we use a Skutt automatic electric kiln...programmable...
>
> Terra cotta is relatively low-fire, yes? And what's the difference
> between
> Flint Hills' terra cotta and red earthenware? I thought they were the
> same
> thing, according to some of my pottery books, but the box lists
> both...what
> I'm using now is fairly groggy, which I like in some instances and in
> others, not so much...
>
> which should net you about an 04 throughout
>
>> your kiln. Then for the glaze firing you can lower the temperature a
>> little if you wish and use an 04 or 05. (Although personally, if you
>> have a kiln sitter kiln, just use the same 03 cones and push it a little
>> closer to the thin side of the cone. You'll get a slightly cooler
>> firing that way and your Duncan glazes should turn out very well there)
>
>
> I have no idea what he glaze fires to, but they seem to turn out well...
>
>> As to your local clay, I'm making an assumption here, but I think when
>> you say "Metro Supply" you are referring to KC Metro,
>
>
> Yes, sorry, I always get the name wrong! And for some reason I
> thought you
> were with them--I was hoping you'd answer.
>
> who uses the same
>
>> clay we do (Flint Hills) the temperatures listed on the box are an
>> overall maturing range for the listed bodies, not a bisque
>> recommendation. Terra Cotta is indeed beautiful at Cone 2, turning a
>> darker brownish red rather than the "flower pot" red that it is at 05.
>
>
> Here is where I am confused, again...hopefully my potter friend/teacher
> won't be. "Overall maturing range" is a term I don't quite understand.
> Does that mean you can fire up to that temp, shouldn't fire higher,
> bisque
> or glaze firing...? Cumulative? Sorry, I am SUCH a dork when it
> comes to
> the mechanics of this stuff, and numbers and I are virtual stramgers...
>
>> You can certainly still bisque it with the kids work, then use
>> underglazes to decorate and glaze fire to Cone 2. The tricky part is
>> finding a clear glaze at Cone 2. I don't know of one available
>> commercially. You'll probably have to find a recipe for one and mix it
>> up yourself.
>> I hope this helps!
>
>
> Hmmm...yes, thank you--but sounds like I might be better off sticking to
> what I'm doing now and developing a bit of patience with the firing
> schedule. I like the nice deep red-brown and the higher vitrification
> (can you refer to ^2 as vitrified? Feels less porous, anyway...)
>
> Interestingly, even when I have the kiln all to myself, we get a
> variety of
> reds and red-browns, no matter what the setting. Must be that uneven
> kiln
> heat/stacking that we've been discussing.
>
>> Cindy Bracker
>> Bracker's Good Earth Clays, Inc.
>
>
> So where are you? I'm in Excelsior Springs, MO...
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
> http://www.cathyjohnson.info/
> http://www.epsi.net/graphic/
> http://www.ebsqart.com/Artists/cmd_1494_profile.htm
>
> ______________________________________________________________________________
>
> 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.
>
>
Jon Pacini on fri 15 oct 04
Greetings All----- Hi Lee
There are lots of once fired earthenware traditions. Most unglazed
earthenware such as Native American/pre-Columbian earthenware is once fired
earthenware. Ivor s example of galena glazed European earthenware is an
interesting example of a different tradition.
The reasoning behind doing a ^04 bisque for todays commercially produced
earthenware stem from two common situations. One--the use of talc as the
basis of many earthenware bodies. Two----the quite stiff unleaded glazes
commonly crammed down our throats by people who don t think potters are
capable of using lead safely. I hope that doesn t sound too opinionated.
The talc bodies gas like crazy. No the clay doesn t actually have gas in it,
as was suggested by someone, but the carbonates and sulfates associated with
Talc are liberated as gasses when the body is fired. By bisque firing hotter
than the glaze temperature, you theoretically burn out the material that
out-gasses at that temperature. Then when you glaze fire at a lower
temperature with stiff, unleaded glazes that don t easily heal over, you won
t get pin holing and blistering of the glaze.
Lee brought up another point, which Ron covered quite well, that is dunting
at low bisque. Porcelains and white stonewares seem to have a tendency to
dunt when low bisqued. I would concur that it s associated with the free
silica and thermal shock. It probably isn t limited to porcelains and white
stoneware, but those bodies most commonly exhibit this fault. Did Ron and I
really agree on that ---wow.
There was also the mention in another post of Raku, and that you can t
bisque raku at ^04 or rather that it isn t desirable to do so. A few weeks
ago there were some postings on pop outs and at the time I noted a problem I
have encountered with what I feel is flint, rather than lime, popping off in
Raku. This problem can be resolved by bisque firing Raku ware to ^04. The
potters having the problems have over come them by using this procedure.
Lastly of the 140 various bodies that Laguna makes, none of them has a
problem being overly vitreous at ^04. They all take glaze application quite
well. If you are used to having very low specific gravities with your
glazes, then you may have to thicken them up some, but I haven t really seen
a problem applying glaze to most clays till they are fired approaching ^02.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Kate Johnson on fri 15 oct 04
Hi Cindy!
> 1. Terra Cotta vs. Earthenware Red: There are 2 answers here. The
> actual terms are more or less synonymous. Terra Cotta is Latin meaning
> burnt earth. Answer number 2 (which is more to the point) is that in
> the Flint Hills Brand, Terra Cotta has 18% grog whereas Earthenware Red
> has no grog. Otherwise, they are essentially the same clay body.
Thanks, that's what I thought, but wanted to make sure. So it's the grog in
the Flint Hills terra cotta that makes it able to mature at a higher temp
(see, I'm learning terms!)
> 2. KC Metro is a different company located in Kansas City, MO on 350
> Highway. I am with Bracker's Good Earth Clays, located in Lawrence, KS
> (loosely a suburb of Kansas City) Their business is a little more
> geared toward hobby ceramics whereas we are more geared toward potters.
> There is some cross-over on both sides, but it's generally friendly
> competition.
That's nice! KC Metro supplies the Excelsior Springs School District, so
that's who I'm familiar with. Bracker's sounds like a great day-trip!
> 3. "Overall Maturing Range" refers to the ultimate firing temperature
After the clay is bisqued, you can apply
> decoration (glazes or underglazes or whatever) and then fire it to the
> maturing temperature.
Ah, thank you...That I understand--though with our relatively low-fire
glazes, we'll see how that works...
Of course there is also single firing, but that's
> a whole different discussion. I hope this helps a little. You're
> welcome to call and discuss uneven firing, bisque temps, terms etc. with
> me if you like. Our toll-free number is (888) 822-1982.
Thank you, I'm sure I will!
Or you might
> consider coming in. Excelsior Springs is not too far from Lawrence and
> we've got some really good restaurants, a beautiful old-fashioned
> downtown shopping district, great museums and galleries etc. down here
> too!
Is the Bluebird Cafe still on Mass Avenue? Yep, Patti Delano and I
co-authored Kansas Off the Beaten Path (at least the first several editions)
for Globe Pequot Press, and I got to write about Lawrence. Stayed in a B&B,
ate in some great little restaurants, visited the museums at KU. It's a
wonderful little town with just enough of the cosmopolitan college town
atmosphere to make it interesting. Definitely sounds like I need to squeeze
in a daytrip...
So do YOU carry colored slip??
Best--
Kate
Lee Love on fri 15 oct 04
Kate Johnson wrote:
>
> As I've mentioned, I fire things in the electric kiln at school, and
> have to
> fit my stuff in around the kids' firing schedules. They use white
> earthenware exclusively, which Metro Supply's box suggests bisquing at
> ^06-04. I'm using terra cotta, which the box says to bisque at. ^06-2.
> Originally, I had mine fired WITH the kids' stuff, at the lower temps,
> but
> discovered it feels stronger, less porous, and even rings if fired to
> ^2, so
> now I'm really trying to wait till I have almost a kilnful of my own.
Hi Kate, what temp do you glaze fire to? If you glaze at a lower
temp, do you get a good glaze covering with the cone 2 bisque? It is
a commercial practice with some ware to bisque at a higher temp and
glaze at a lower temp. You might need to add something to the glaze
like David H does for once firing, to get a good glaze covering.
A friend of mine used Continental Clay terracotta to make an
outdoor sculpture. She was told to fire it to cone 1 if she wanted
it to be durable against the weather. But she did not glaze the work,
using stains to color it instead.
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
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