timothy knick on sat 10 feb 07
Does anyone know what would happen if I were to clear glaze the inside of a teapot, leave the outside bare, fire it to cone ten, remove it and put it into a barrel full of sawdust or shredded paper? Would the outside be an ashy mess?
Tim
---------------------------------
Don't pick lemons.
See all the new 2007 cars at Yahoo! Autos.
Marcia Selsor on sat 10 feb 07
On Feb 10, 2007, at 1:29 PM, timothy knick wrote:
> Does anyone know what would happen if I were to clear glaze the
> inside of a teapot, leave the outside bare, fire it to cone ten,
> remove it and put it into a barrel full of sawdust or shredded
> paper? Would the outside be an ashy mess?
> Tim
>
No ashy mess. The whole thing would crack from the shock of a vitrified
clay body undergoing such extreme rapid temperature changes.
Marcia Selsor
http://marciaselsor.com
Dannon Rhudy on sat 10 feb 07
It would not be an ashy mess, exactly. That is, any ash
would just rinse off, because the clay is vitrified. For the
same reason, the clay will absorb little or no carbon -
it is already vitrified. The clay must be porous to some
extent to absorb carbon from the firing. There is not
any reason you can't try it, but no doubt it has been tried
many times before. There are ways to put a raku-temp
glaze on the pot after it is fired to cone 10 - then it can
be re-fired to raku temps. The problems are these:
the piece is extremely likely to crack or explode, because
vitrified clay doesn't respond well to rapid heating and
cooling; and, again, if it does make it through the raku
firing, it will not absorb any carbon, or any to speak of,
when you put it into a container with combustibles. It
doesn't work well, in short.
regards
Dannon Rhudy
Subject: hi fire and then raku?
> Does anyone know what would happen if I were to clear glaze the inside of
a teapot, leave the outside bare, fire it to cone ten, remove it and put it
into a barrel full of sawdust or shredded paper? Would the outside be an
ashy mess?
> Tim
>
>
> ---------------------------------
> Don't pick lemons.
> See all the new 2007 cars at Yahoo! Autos.
>
>
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__
> Send postings to clayart@lsv.ceramics.org
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>
Tony on sun 11 feb 07
If it was a raku clay body, with plenty of grog or sand, it should withstand
the temperature shock
Tony Schlosser
Sydney Australia
(where the sun is shining)
----- Original Message -----
From: "Marcia Selsor"
To:
Sent: Sunday, February 11, 2007 8:26 AM
Subject: Re: hi fire and then raku?
> On Feb 10, 2007, at 1:29 PM, timothy knick wrote:
>
> > Does anyone know what would happen if I were to clear glaze the
> > inside of a teapot, leave the outside bare, fire it to cone ten,
> > remove it and put it into a barrel full of sawdust or shredded
> > paper? Would the outside be an ashy mess?
> > Tim
> >
> No ashy mess. The whole thing would crack from the shock of a vitrified
> clay body undergoing such extreme rapid temperature changes.
>
> Marcia Selsor
> http://marciaselsor.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.
>
Lee Love on sun 11 feb 07
On 2/11/07, Dannon Rhudy wrote:
. The problems are these:
> the piece is extremely likely to crack or explode, because
> vitrified clay doesn't respond well to rapid heating and
> cooling;
Have you actually SEEN this happen? Because of the nature of
my fireboxes in my woodkiln, it is easy to put pot into the ash pit
and pull them out. I have been experimenting with this. Only
thing you have to be careful about already glazed fired pots, is that
you heat them up slowly, by first placing them in the firebox, as far
away from the ashes as possible. Then you turn the pot to heat the
other side. After a few minutes, I use re-rod bent to a hook at one
end, to push the pot in a little farther. I move the pot into the ash
pit in about 3 stages. Pulling them out is no problem. I put them
in a sagger. I have never had any explode, pulling them out.
and, again, if it does make it through the raku
> firing, it will not absorb any carbon, or any to speak of,
> when you put it into a container with combustibles. It
> doesn't work well, in short.
Carbon does effect bare clay and will work its way into any
crazing. I plan on more experiments and will post photos when I do
them.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Snail Scott on sun 11 feb 07
At 11:29 AM 2/10/2007 -0800, you wrote:
>Does anyone know what would happen if I were to clear glaze the inside of
a teapot, leave the outside bare, fire it to cone ten, remove it and put it
into a barrel full of sawdust or shredded paper? Would the outside be an
ashy mess?
Remove it AT ^10? Yikes! Unless the clay
body contans massive amounts of kyanite or
some such, I think thermal shock might do
it in. There's a reason why folks don't
raku with vitrified clay, or even semi-
vitrified earthenware. And clay that's
vitrifies at ^10 is likely gonna have
cristobalite and such which will exacerbate
the problem. Also, I suspect that although
you might possibly get some fused chunks
stuck to your surface, vitrified clay won't
tend to absorb smoke like unvitrified clay
can, so it'll be a bit grayish at most.
-Snail
Craig Clark on sun 11 feb 07
Lee, coupla questions: First, when you pull the pots from the kiln at
high temp how hot are they? Is the high fire glaze molten? Also, how
long does the pot remain in the open atmosphere before you place them in
the saggar? Is the saggar relatively small or is it larger? Do you then
seal the saggar as you would any common post firing reduction vessel for
raku? I'm looking forward to seeing the results.
I have taken a number of vessels that I only fired as high as a cone
two. They were left unglazed. I then put them into the barrel to see how
much carbon deposition that I could get. My intent was to make "tougher"
raku. The idea being the closer I could fire to the vitrification point
of the clay body, the stronger the pot would be, though I had a number
of associated concerns about the pots cracking from the thermal shock if
the clay was fully vitrified, not too mention the fact that the raku
glazes I have will burn off the pot at high fire temps.
I did not have much luck affecting a nice black carbon burn in at the
higher temps. I flamed conciderably longer than I normally would have
but still did not get what I was after and could easily achieve at the
lower temp. Have you been able to get a nice blackened surface from
carbon deposition on a vitrified clay body?
Craig Dunn Clark
619 East 11 1/2 St
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
AreLee Love wrote:
> On 2/11/07, Dannon Rhudy wrote:
>
> . The problems are these:
>> the piece is extremely likely to crack or explode, because
>> vitrified clay doesn't respond well to rapid heating and
>> cooling;
>
> Have you actually SEEN this happen? Because of the nature of
> my fireboxes in my woodkiln, it is easy to put pot into the ash pit
> and pull them out. I have been experimenting with this. Only
> thing you have to be careful about already glazed fired pots, is that
> you heat them up slowly, by first placing them in the firebox, as far
> away from the ashes as possible. Then you turn the pot to heat the
> other side. After a few minutes, I use re-rod bent to a hook at one
> end, to push the pot in a little farther. I move the pot into the ash
> pit in about 3 stages. Pulling them out is no problem. I put them
> in a sagger. I have never had any explode, pulling them out.
>
> and, again, if it does make it through the raku
>> firing, it will not absorb any carbon, or any to speak of,
>> when you put it into a container with combustibles. It
>> doesn't work well, in short.
>
> Carbon does effect bare clay and will work its way into any
> crazing. I plan on more experiments and will post photos when I do
> them.
>
> --
> Lee in Mashiko, Japan
> Minneapolis, Minnesota USA
> http://potters.blogspot.com/
>
> "To affect the quality of the day, that is the highest of arts." -
> Henry David Thoreau
>
> "Let the beauty we love be what we do." - Rumi
>
> ______________________________________________________________________________
>
> 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 sun 11 feb 07
Dear Snail;
While I would do not carbonize my cone 10/11 pull-outs, I do use a
weathered andesite 94%/wood ash 6% glaze on my teabowls, which would be
dark scummy and iron saturated if left to cool in the kiln. Since I
pull them from the stoke holes and allow them to cool in air(or under a
fiber-lined bucket), they turn out jet black and satiny...... because
the iron is trapped in solution and cannot precipitate to the surface.
They make fine chawan, with the frothy lime green tea a lovely contrast
with the jet black, and the unwashed wood ash also promotes a lovely
'raven's wing' irridescence. None have cracked in cooling. This is the
way it was done around Seto four hundred years ago, and many other
places since.
Cheers, Hank
www.murrow.biz/hank
On Feb 11, 2007, at 7:57 AM, Snail Scott wrote:
> At 11:29 AM 2/10/2007 -0800, you wrote:
>> Does anyone know what would happen if I were to clear glaze the
>> inside of
> a teapot, leave the outside bare, fire it to cone ten, remove it and
> put it
> into a barrel full of sawdust or shredded paper? Would the outside
> be an
> ashy mess?
>
>
> Remove it AT ^10? Yikes! Unless the clay
> body contans massive amounts of kyanite or
> some such, I think thermal shock might do
> it in. There's a reason why folks don't
> raku with vitrified clay, or even semi-
> vitrified earthenware. And clay that's
> vitrifies at ^10 is likely gonna have
> cristobalite and such which will exacerbate
> the problem. Also, I suspect that although
> you might possibly get some fused chunks
> stuck to your surface, vitrified clay won't
> tend to absorb smoke like unvitrified clay
> can, so it'll be a bit grayish at most.
>
> -Snail
>
> _______________________________________________________________________
> _______
> 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 sun 11 feb 07
At 06:38 PM 2/11/2007 +0900, you wrote:
>...Pulling them out is no problem. I put them
>in a sagger. I have never had any explode, pulling them out...
I wouldn't expect an explosion, per se,
but no dunting cracks? Nice!
According to the present wisdom the
critical phase in cooling from high
firing is quartz inversion, which is
actually a pretty low temperature,
barely red hot. It could be that if
something were well saggared while still
red hot, the cooling might be adequately
slowed to a safe speed. A compact,
consistent-walled form should also be
sturdier than something with an irregular
form. Classic tea bowls would seem a
pretty good shape, in fact: small, round,
no attachments, footed, and groggy.
I suspect that the clay body is a pretty
important factor as well.
-Snail
Snail Scott on sun 11 feb 07
At 09:53 AM 2/11/2007 -0800, Hank M wrote:
>...I
>pull them from the stoke holes and allow them to cool in air...None have
cracked in cooling...
They sound gorgeous. What kind of clay body
are you using, and do you think that there
is much cristobalite formation? (I think
that's a factor.)
I also suspect that tea bowls of the classic
type are probably ideal for this - compact,
round, footed, lacking attachments, and
usually groggy. Have you had any forms that
did badly?
-Snail
Lee Love on sun 11 feb 07
On 2/11/07, timothy knick wrote:
> Does anyone know what would happen if I were to clear glaze the inside of a teapot, >leave] the outside bare, fire it to cone ten, remove it and put it into a barrel full of
>sawdust or shredded paper? Would the outside be an ashy mess?
This is called hikidashi. It was developed at the same time as raku.
The iron saturated glazed pot is pulled from the kiln at stoneware
temps to cool (without reduction materials) rapidly so the iron does
not recrystallize and become mat. See archives for past discussion.
See an example of Hank's hikidashi black:
http://claycraft.blogspot.com/2006/01/hanks-hikidashi-seto-guro-trycone-12.html
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Lee Love on mon 12 feb 07
Craig & Snail,
On 2/12/07, Craig Clark wrote:
> Lee, coupla questions: First, when you pull the pots from the kiln at
> high temp how hot are they? Is the high fire glaze molten?
I have pulled them at various temps, probably as high as cone 13.
Sometimes the glaze is molten. This really isn't a problem.
Japanese have been doing this for 400 years.
They probably started from pulling test tiles. If you have
ever pulled a ring from a salt kiln, you know they don't explode or
dunt.
Also, how
> long does the pot remain in the open atmosphere before you place them in
> the saggar? Is the saggar relatively small or is it larger? Do you then
> seal the saggar as you would any common post firing reduction vessel for
> raku? I'm looking forward to seeing the results.
I set them right on the plate sagger in the open. I use the
open sagger simily as a non-flamable place to set them. Also, you
have to realize, you need longer tongs or extra insulation because
these objects are radiating more heat than in raku.
> I did not have much luck affecting a nice black carbon burn in at the
> higher temps. I flamed conciderably longer than I normally would have
> but still did not get what I was after and could easily achieve at the
> lower temp. Have you been able to get a nice blackened surface from
> carbon deposition on a vitrified clay body?
I try to avoid the black carbon. Japanese aren't crazy
about it. But it happens. You might think about trying different
slips or mat glazes.
I haven't used any special clays. Just Mashiko and
Shigaraki. Mashiko is high in silica and is vulnerable to dunting,
but I haven't had any trouble with it.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
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