mel jacobson on wed 23 mar 05
i really believe that bisque firing is the source
of a great many clay problems...or, the result of.
the older i get, the more information i gather, i more
and more am understanding that how we dry, heat,
bisque our pots is critical to making final well crafted
ceramics.
at dinner the other night with feriz at the helm, we asked
some very good questions about `quartz inversion` etc.
(poor ken almost got blown over.)
feriz is very firm about some of these questions.
i will not get into a techno fight right now...but he
claims it does not happen in industry. he claims that glaze
firing can be as fast as you want it to be, as long as you
have done the bisque firing properly. he claims that in some
cases, ceramics are fired to high temp in minutes. give or take twenty.
nils has always said to fire your kiln as fast as you want during
glaze firing. turn it to high to start. all switches to high..get rid
of the controller. but, learn how to factor in slow cooling.
because industry pre/heats all clay before it is bisque fired....and
bisque firing is slow and controlled...pots never crack or warp. they
never pin hole. (or at least the loss factor is very low.)
feriz suggests that all potters stack greenware on top of your kilns
during bisque or glaze firing. the more you are able to drive off
water during this period the better it is. remember that chemical water
is driven off at high heat, but real water evaporates very well from outside
heat sources.
i have done this for almost thirty years. i never fire a bisque kiln without
a load of tomorrows pots on top. i just make a pyramid. heavy pots on the
outside wall area, working to lighter mugs etc in the center.
my bisque kiln is 40 years old, and has no cracks in the lid, so i assume
it is safe. i know that driving off water is the salvation to great bisque
firing. why waste all that heat? use it to drive off water. i pack my
bisque firings with hot pots....and still fire very slowly. i rarely have
a crack
and glaze flaws are kept to a minimum during glaze firing. i make rough
pots, so some of the flaws never show anyway.
far too many potters worry about the final cone number when
firing bisque...and forget the steps that proceed the firing.
it is not the final cone number that counts the most. it is pre/heating,
slow bisque firing and care of greenware. slow drying of tight bodies
is very important. that is why i always add grog and sand to my clay.
tooth and drying properties. important stuff.
some potters build in faults even before pots are made....they use
clay that should be used for casting for hand building and throwing.
they use clay that is not suited to them...and then complain for
years about problems.
if anything has ever been said on clayart that is more important
than this issue, i would love to know what it is. the work of
ron roy with clay, david b, jon pancini....years of experience, and few
listen. they just say...`oh, i use bmix, or lg2756, and it works ok.
not knowing a thing about what they are doing. i have learned so
much from ron...and man, do i listen. i love the banter between
ron and jon pancini...both very smart guys with clay. read it, listen
to them...try and keep up. how much i appreciate what david baumee
and others are working on with porcelain. wonderful work.
in my interview with j.t. abernathy he was so emphatic about
the insanity of `broad range clay bodies`. he said...it cannot happen.
each clay body should be made for the work it is intended. it should
be a one cone body...if you fire to cone 11, make your clay for cone 11.
when you fire with deep reduction, clay bodies go to hell fast. you
should match a heavy reduction body with a heavy reduction clay.
the reason joe and i can take our iron bearing clay and glaze to
cone 13 is that we do not reduce. that is the key. i fuss so much
over the drying of these pots, preheat the pots, load the bisque with
gloves as the pots are so hot. slow bisque firing. it is the steps that
count...the early steps.
many potters only think...GLAZE, GLAZE, GLAZE, WHAT NEXT?
don't do that. think CLAY CLAY CLAY. and how to prepare my
pots for glaze.
some of the oldest myth fabrications in ceramics are bisque related.
much is silly myth.
the new ideas are critical...use them.
mel
mel jacobson/minnetonka/minnesota/usa
http://www.pclink.com/melpots
http://www.rid-a-tick.com
luckisprepaid
Pfeiffer, Dan R (Dan) on wed 23 mar 05
>> mel said
i have done this for almost thirty years. i never fire a bisque kiln
without
a load of tomorrows pots on top.
<<
We have been working on doing a slow bisque and run the pilot to preheat
the kiln over night to about 300. As we only have a updraft to do all our
work in, pots on top would not work so well any ideas what else could be
done in place of using the top?
Dan & Laurel
Craig Martell on wed 23 mar 05
Hello mel et al:
In response to your statement about "the final cone number" being less
important than preheating and slow firing I would respectfully say: "mebbe
not". All are important, but it depends on the kind of clay you use and
the kind of pots made.
I had a lot of cracking of flatware and platters from dinner plates to 24
inch platters when I bisque fired to cone 06. I don't load ware until it's
totally dry and I fire slowly. But I still had significant amounts of
cracking and it hurts to lose the big stuff.
I fire porcelain bodies which contain a lot of china clay and this stuff is
refractory. More so than most stoneware and earthenware bodies that
contain some natural fluxes. So, I was seeing these big pots go belly up
and realized they were cooling dunts not cracks on the way up. What
happens is the bodies are a loose configuration during heating. The clay
is still kaolin. After passing the 1300 to 1400 degree F range the
hydroxyls collapse, which means the clay loses chemically bound water, and
you have metakaolin instead of natural kaolinite clay. The claybody is a
tighter structure on the way down and if there larger pots and even medium
size flatware hasn't been fired hot enough to sinter the feldspar there
will not be sufficient fired strength and the pots will dunt when the pass
thru the quartz inversion on the way back down. Two ways to avoid this
problem are: fire the bisque to a hot enough temp to gain fired strength,
or single fire. Stacking helps too. Don't "nest" the pots but "box" them
which is stacking rim to rim, foot to foot.
I bisque my body to cone 03. No dunts and the glazes still apply just fine
at the consistency I was using at cone 06.
regards, Craig Matell Hopewell, Oregon
Jennifer Boyer on wed 23 mar 05
I have my bisk kiln in a small room just big enough for the kiln, one
ware rack and my pug mill with plaster bats above it. So the room gets
nice and toasty and dries the pots on the ware rack as well as the
plaster bats and whatever slop is on them. It has a powerful exhaust
fan and a window that I keep open when the fan is running. Works for
me!
Also I try to load a bisk so that I can put it on low for an hour and
then turn it off overnight before firing. Does a nice job of predrying
the pots...
Jennifer
On Mar 23, 2005, at 3:48 PM, Pfeiffer, Dan R (Dan) wrote:
>>> mel said
> i have done this for almost thirty years. i never fire a bisque kiln
> without
> a load of tomorrows pots on top.
> <<
>
> We have been working on doing a slow bisque and run the pilot to
> preheat
> the kiln over night to about 300. As we only have a updraft to do all
> our
> work in, pots on top would not work so well any ideas what else
> could be
> done in place of using the top?
>
> Dan & Laurel
>
> _______________________________________________________________________
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>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Richard Aerni on wed 23 mar 05
Hi,
Just to piggyback a bit on the comments of Craig Martell below, in relation
to cracking bisqueware vs. single firing.
In another lifetime (well, 20 years ago) I was in a partnership with two
other potters, and we produced a number of large murals, fountains, etc, the
largest being 45 feet x 90 feet and using over 30,000 pounds of clay. We
were feeling our way along on that first large commission, never having
undertaken anything of that scale before, and figured with all of our carved
tiles (12 inches by 12 inches) being one of a kinds, that bisque firing them
would be the safer way to go. When we were firing up our first test panel,
a six foot by eight foot mural, all of the pieces, every single one, cracked
in the bisque. We were beside ourselves with anxiety, but deadlines were
deadlines, and the thing needed to be fired. We next tried to single fire
the pieces, and that worked like a charm. Of all of the thousands of
sculpted pieces, we didn't have a single one crack.
Craig's explanation makes a lot of sense to me. Sometimes single firing is
the best and easiest way to go.
Best,
Richard Aerni
Rochester, NY
On Wed, 23 Mar 2005 13:48:06 -0800, Craig Martell wrote:
>I had a lot of cracking of flatware and platters from dinner plates to 24
>inch platters when I bisque fired to cone 06. I don't load ware until it's
>totally dry and I fire slowly. But I still had significant amounts of
>cracking and it hurts to lose the big stuff.
>
>I fire porcelain bodies which contain a lot of china clay and this stuff is
>refractory. More so than most stoneware and earthenware bodies that
>contain some natural fluxes. So, I was seeing these big pots go belly up
>and realized they were cooling dunts not cracks on the way up. What
>happens is the bodies are a loose configuration during heating. The clay
>is still kaolin. After passing the 1300 to 1400 degree F range the
>hydroxyls collapse, which means the clay loses chemically bound water, and
>you have metakaolin instead of natural kaolinite clay. The claybody is a
>tighter structure on the way down and if there larger pots and even medium
>size flatware hasn't been fired hot enough to sinter the feldspar there
>will not be sufficient fired strength and the pots will dunt when the pass
>thru the quartz inversion on the way back down. Two ways to avoid this
>problem are: fire the bisque to a hot enough temp to gain fired strength,
>or single fire. Stacking helps too. Don't "nest" the pots but "box" them
>which is stacking rim to rim, foot to foot.
Kathi LeSueur on wed 23 mar 05
Craig Martell wrote:
> Hello mel et al:
>
> In response to your statement about "the final cone number" being less
> important than preheating and slow firing I would respectfully say: "mebbe
> not". All are important, but it depends on the kind of clay you use and
> the kind of pots made.
>
> I had a lot of cracking of flatware and platters from dinner plates to 24
> inch platters when I bisque fired to cone 06. I don't load ware until
> it's
> totally dry and I fire slowly. But I still had significant amounts of
> cracking and it hurts to lose the big stuff.
I think there is no "right" bisque temperature, just the "right" bisque
temperature for you. Finding that temperature and firing cycle takes
time. What Mel does works for him and his clay. What Craig does works
for his clay. I, also, had lots of cracking problems in my large
platters. I found that increasing the temperature to 05 up from 06 took
care of the problem. There are no quick easy answers in this business.
The people who take the time to experiment, and who are willing to
listen to the advice from others, will usually be able to solve their
problems.
Kathi
Mark Tigges on wed 23 mar 05
On Wed, Mar 23, 2005 at 04:26:40PM -0500, Jennifer Boyer wrote:
> Also I try to load a bisk so that I can put it on low for an hour and
> then turn it off overnight before firing. Does a nice job of predrying
> the pots...
I like this idea a lot. Why didn't I think of it? Thanks Jenn
sincultura13 on thu 24 mar 05
"Two ways to avoid this
problem are: fire the bisque to a hot enough temp to gain fired
strength, or single fire."
I get the logic behind going for a higher temp bisque or Lee's
comment on single firing to get more clay interaction with the
glaze...but could you further explain why singles firing helps in
this case? BTW, there's no sarcasm what so ever in my question, I'm
a newbie reasoning this subject for the first time.
thanks in advance
Sincultura
Lee Love on thu 24 mar 05
>I get the logic behind going for a higher temp bisque or Lee's
>comment on single firing to get more clay interaction with the
>glaze...but could you further explain why singles firing helps in
>this case?
>
>
Many of the variations in glazes that commercial ceramics goes
to extremes to avoid are desirable in high fired, especially wood fired
pottery.
Because the organics and other volatiles are venting
from the clay into the glaze during the early part of single firing,
they have a chance of interacting with the glaze. This is the same
thing that causes problems at lower temperatures. But at higher
temps, things like craters and pinholes have a chance to heal over.
--
in Mashiko, Japan http://mashiko.org
http://potters.blogspot.com/ WEB LOG
http://claycraft.blogspot.com/ Photos!
Lee Love on thu 24 mar 05
Craig Martell wrote:
> In response to your statement about "the final cone number" being less
> important than preheating and slow firing I would respectfully say:
> "mebbe
> not". All are important, but it depends on the kind of clay you use and
> the kind of pots made.
The variables are numerous. Not only is your clay a
factor, but also what temperature you glaze fire to and and for how
long you fire your glaze firing needs to be taken into account..
Hotter, longer glaze firings are more forgiving. And you just might
want some of that activity coming up from the clay body to add richness
to the glaze.. It is one reason why I do some single firing.
I learned to bisque from Japanese potters. The first,
being at potter at NCC who bisqued at 012. But then later here in
Mashiko, where the bisque in the noborigama varies from 012 to dull red
heat, a bit below 012.
Remember, industry wants uniformity and consistency and no
loss. If you follow their practices, your work will look more like
their's. If you want the variability you find in traditional
work, you need to look at how they did things. Their processes are
responsible for the way their work looks.
An important element I have found in single firing with ash and
soda ash glazes is that the iron content of the clay is very
important. High iron clays don't like to be sealed in early.
The amount of organics in the clay don't seem to be big a
factor. We are taught to dislike this variability by industry. My
clays all have a high level of organics in them, because they are not
"killed" materials. My Shigaraki clay stinks to high heaven in the
summer. I don't have glaze problems, even though my bisque is at a
low temperature.
--
Lee in Mashiko, Japan http://mashiko.org
http://potters.blogspot.com/ WEB LOG
http://claycraft.blogspot.com/ Photos!
Ron Roy on fri 25 mar 05
Hi Sincultura,
The higher bisque firing just makes the ware stronger and this is sometimes
enough to avoid the bisque dunting.
Single firing avoids the problem because the ware does not cool down
through the quartz inversion when it is still fragile (half fired.)
The kind of dunting you get with glazed ware is usually due to too low
expansion of of glazes.
RR
>"Two ways to avoid this
>problem are: fire the bisque to a hot enough temp to gain fired
>strength, or single fire."
>
>
>I get the logic behind going for a higher temp bisque or Lee's
>comment on single firing to get more clay interaction with the
>glaze...but could you further explain why singles firing helps in
>this case? BTW, there's no sarcasm what so ever in my question, I'm
>a newbie reasoning this subject for the first time.
>thanks in advance
>Sincultura
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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