Daniela Rumpf on mon 2 may 11
Hello,
I recently ran into a problem firing my plates in a gas kiln to cone 10.
Almost all the plates cupped. The plates are wheel thrown with a 5% iron
stoneware. I trim one ring foot about 1 inch from the outside edge of the p=
late.
I don't have problems with cracking so I figured my compressing method was
working. I work in my basement so there is no direct source of heat blowing=
on
the greenware during drying and drying is rather slow. The firing in this k=
iln
went a bit fast for my liking: well into red heat within 4 hours and in hea=
vy
reduction. Cone 7 dropping after only another hour. I did slow it down at t=
he
end and had a 10 hour firing. The kiln is fiber lined down draft with 2 for=
ced
air blowers that tends to fire hotter on the bottom. This was only the seco=
nd
time firing this kiln and I don't have a lot of plates to compare this too.=
I
did not previously have this problem but I can't positively say that I have=
n't
changed my throwing and trimming methods. I can say that the clay body and =
kiln
are different.
I would appreciate any input or suggestions for trial runs to figure out =
the
problem.
Thank you,
Daniela Rumpf
Ron Roy on mon 2 may 11
Hi Daniela,
Chances are your clay is being over fired - perhaps because all the
organics have not been burned out during the bisque. Can be a real
problem with iron rich clays.
What cone are you firing your bisque to? Are you using cones? How do
you test to see if there is excess oxygen during bisque firing?
Any sign of bloating on the plates - little bubbles or raised areas anywher=
e?
RR
Quoting Daniela Rumpf :
> Hello,
>
> I recently ran into a problem firing my plates in a gas kiln to cone 10=
.
> Almost all the plates cupped. The plates are wheel thrown with a 5% iron
> stoneware. I trim one ring foot about 1 inch from the outside edge
> of the plate.
> I don't have problems with cracking so I figured my compressing method wa=
s
> working. I work in my basement so there is no direct source of heat
> blowing on
> the greenware during drying and drying is rather slow. The firing in
> this kiln
> went a bit fast for my liking: well into red heat within 4 hours and in h=
eavy
> reduction. Cone 7 dropping after only another hour. I did slow it down at=
the
> end and had a 10 hour firing. The kiln is fiber lined down draft
> with 2 forced
> air blowers that tends to fire hotter on the bottom. This was only the se=
cond
> time firing this kiln and I don't have a lot of plates to compare this to=
o. I
> did not previously have this problem but I can't positively say that
> I haven't
> changed my throwing and trimming methods. I can say that the clay
> body and kiln
> are different.
>
> I would appreciate any input or suggestions for trial runs to
> figure out the
> problem.
>
>
> Thank you,
> Daniela Rumpf
>
David Beumee on mon 2 may 11
Hi Daniela,
Is this a clay body that you have a recipe for? Iron is a flux in a
reducing atmosphere, and 5% in quite high for a cone 10 body. You also
mentioned that the atmosphere was heavy reduction, and that cone 7 fell onl=
y
an hour after reaching red heat. That's way too fast. You've got to slow
down your firing between red heat and top temperature.
If you have a recipe, perhaps I can help.
David Beumee
Porcelain by David Beumee
806 East Baseline Road
Lafayette, CO 80026
www.davidbeumee.com
303-665-6925
On Mon, May 2, 2011 at 8:35 AM, Daniela Rumpf wrote:
> Hello,
>
> I recently ran into a problem firing my plates in a gas kiln to cone 10.
> Almost all the plates cupped. The plates are wheel thrown with a 5% iron
> stoneware. I trim one ring foot about 1 inch from the outside edge of the
> plate.
> I don't have problems with cracking so I figured my compressing method wa=
s
> working. I work in my basement so there is no direct source of heat blowi=
ng
> on
> the greenware during drying and drying is rather slow. The firing in this
> kiln
> went a bit fast for my liking: well into red heat within 4 hours and in
> heavy
> reduction. Cone 7 dropping after only another hour. I did slow it down at
> the
> end and had a 10 hour firing. The kiln is fiber lined down draft with 2
> forced
> air blowers that tends to fire hotter on the bottom. This was only the
> second
> time firing this kiln and I don't have a lot of plates to compare this to=
o.
> I
> did not previously have this problem but I can't positively say that I
> haven't
> changed my throwing and trimming methods. I can say that the clay body an=
d
> kiln
> are different.
>
> I would appreciate any input or suggestions for trial runs to figure out
> the
> problem.
>
>
> Thank you,
> Daniela Rumpf
>
--
Daniela Rumpf on mon 2 may 11
Hi Ron,
your comments make me think that there may be a problem with the bisque. =
i
fired to cone 06 with a kiln sitter and no kiln vent. I am wondering if I a=
m
stacking the plates to high and close. Some of them were discolored in the
center so maybe that is the problem. I don't test for excess oxygen. I have=
not
noticed any bloating of the clay after the high fire.
Thanks,
Daniela
________________________________
From: "ronroy@ca.inter.net"
To: Daniela Rumpf
Cc: Clayart@LSV.CERAMICS.ORG
Sent: Mon, May 2, 2011 7:09:49 PM
Subject: Re: Warped/cupped plates in high fire
Hi Daniela,
Chances are your clay is being over fired - perhaps because all the organic=
s
have not been burned out during the bisque. Can be a real problem with iron=
rich
clays.
What cone are you firing your bisque to? Are you using cones? How do you te=
st to
see if there is excess oxygen during bisque firing?
Any sign of bloating on the plates - little bubbles or raised areas anywher=
e?
RR
Quoting Daniela Rumpf :
> Hello,
>
> I recently ran into a problem firing my plates in a gas kiln to cone 10=
.
> Almost all the plates cupped. The plates are wheel thrown with a 5% iron
> stoneware. I trim one ring foot about 1 inch from the outside edge of the
>plate.
> I don't have problems with cracking so I figured my compressing method wa=
s
> working. I work in my basement so there is no direct source of heat blowi=
ng on
> the greenware during drying and drying is rather slow. The firing in this=
kiln
> went a bit fast for my liking: well into red heat within 4 hours and in h=
eavy
> reduction. Cone 7 dropping after only another hour. I did slow it down at=
the
> end and had a 10 hour firing. The kiln is fiber lined down draft with 2 f=
orced
> air blowers that tends to fire hotter on the bottom. This was only the se=
cond
> time firing this kiln and I don't have a lot of plates to compare this to=
o. I
> did not previously have this problem but I can't positively say that I ha=
ven't
> changed my throwing and trimming methods. I can say that the clay body an=
d
kiln
> are different.
>
> I would appreciate any input or suggestions for trial runs to figure ou=
t the
> problem.
>
>
> Thank you,
> Daniela Rumpf
>
Bonnie Staffel on tue 3 may 11
I don't recall ever having this problem of the wall or flange on a =3D
platter
or bowl warp up on me. However, the last firing I did, because I had =3D
some
previously glazed and fired pots in the kiln, I selected the FAST glaze =3D
fire
mode. Never should have done that. I had a very nice big bowl with a =3D
wide
flange and one side came out of the kiln with it drastically warped up. =3D
Must
have been closer to the elements in the electric kiln. When setting the
controller, I recall my thoughts were divided about whether to do this =3D
or
not and I really should not have done it. Now I have a big warped bowl =3D
that
is not saleable nor do I need one for myself. My clay was rated as Cone =3D
8 -
10 and I fired this at a good Cone 9 tip touching and 10 starting to =3D
bend.=3D20
=3D20
Lesson learned.=3D20
=3D20
Bonnie
=3D20
=3D20
=3D20
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Introduction to Wheel Work
Charter Member Potters Council
=3D20
David Finkelnburg on tue 3 may 11
Daniela,
A new clay body is more likely the cause than a different kiln. It is
difficult to tell in detail what is going on without actually seeing the
plates. Photos would be the next best thing. Can you e-mail off-list or pos=
t
pictures somewhere?
In general, *all* warping in a firing (not slumping/bloating) is caused
by shrinkage at different rates in different parts of the ware. This
differential shrinkage is *usually* caused by differential density in the
ware before it goes into the kiln.
For example, as you know it is quite possible for clay in the center of
a plate to be stretched much less in the throwing/forming process than clay
at the rim. The more the clay is stretched in forming the more it tends to
shrink in firing. Thus, the rim tends to shrink more than the center and in
the process the rim will curl up. However, if this is happening in your cas=
e
it would usually be at least somewhat apparent in the drying process, or yo=
u
would be getting "S" cracking in the foot, or both, and that doesn't sound
like what's happening. Therefore it sounds like some alternative explanatio=
n
such as has been offered may be causing more shrinkage at the rim than the
foot.
To diagnose the problem you have to find the cause of the differential
shrinkage.
Good potting!
Dave Finkelnburg
http://www.mattanddavesclays.com
-----------------------------
On Mon, 2 May 2011 07:35:57 -0700, Daniela Rumpf wrote
I recently ran into a problem firing my plates in a gas kiln to cone 10.
Almost all the plates cupped. The plates are wheel thrown with a 5% iron
stoneware. I trim one ring foot about 1 inch from the outside edge of the
plate.
I don't have problems with cracking so I figured my compressing method was
working. I work in my basement so there is no direct source of heat blowing
on
the greenware during drying and drying is rather slow. The firing in this
kiln
went a bit fast for my liking: well into red heat within 4 hours and in
heavy
reduction. Cone 7 dropping after only another hour. I did slow it down at
the
end and had a 10 hour firing. The kiln is fiber lined down draft with 2
forced
air blowers that tends to fire hotter on the bottom. This was only the
second
time firing this kiln and I don't have a lot of plates to compare this too.
I
did not previously have this problem but I can't positively say that I
haven't
changed my throwing and trimming methods. I can say that the clay body and
kiln
are different.
Ron Roy on tue 3 may 11
Hi Daniela,
Sounds like that may be the problem - either that or the clay may not
be formulated properly for cone 10.
If there are organics present and they are not burned off - they will
rob any iron present of oxygen turning it into FeO which then become a
strong flux.
Stack the plates with spaces between them - leave a top spy open and
bisque to cone 04 - not fast (not over 50C per hour) especially after
700C - give the organics time to burn out.
Watch out for any signs of cristobalite - like glazes shivering -
those high iron bodies can have a lot.
RR
Quoting Daniela Rumpf :
> Hi Ron,
>
> your comments make me think that there may be a problem with the bisque=
. i
> fired to cone 06 with a kiln sitter and no kiln vent. I am wondering if I=
am
> stacking the plates to high and close. Some of them were discolored in th=
e
> center so maybe that is the problem. I don't test for excess oxygen.
> I have not
> noticed any bloating of the clay after the high fire.
>
>
> Thanks,
> Daniela
>
>
>
>
> ________________________________
> From: "ronroy@ca.inter.net"
> To: Daniela Rumpf
> Cc: Clayart@LSV.CERAMICS.ORG
> Sent: Mon, May 2, 2011 7:09:49 PM
> Subject: Re: Warped/cupped plates in high fire
>
> Hi Daniela,
>
> Chances are your clay is being over fired - perhaps because all the organ=
ics
> have not been burned out during the bisque. Can be a real problem
> with iron rich
> clays.
>
> What cone are you firing your bisque to? Are you using cones? How do
> you test to
> see if there is excess oxygen during bisque firing?
>
> Any sign of bloating on the plates - little bubbles or raised areas anywh=
ere?
>
> RR
>
> Quoting Daniela Rumpf :
>
>> Hello,
>>
>> I recently ran into a problem firing my plates in a gas kiln to cone 1=
0.
>> Almost all the plates cupped. The plates are wheel thrown with a 5% iron
>> stoneware. I trim one ring foot about 1 inch from the outside edge of th=
e
>> plate.
>> I don't have problems with cracking so I figured my compressing method w=
as
>> working. I work in my basement so there is no direct source of heat
>> blowing on
>> the greenware during drying and drying is rather slow. The firing
>> in this kiln
>> went a bit fast for my liking: well into red heat within 4 hours
>> and in heavy
>> reduction. Cone 7 dropping after only another hour. I did slow it
>> down at the
>> end and had a 10 hour firing. The kiln is fiber lined down draft
>> with 2 forced
>> air blowers that tends to fire hotter on the bottom. This was only
>> the second
>> time firing this kiln and I don't have a lot of plates to compare
>> this too. I
>> did not previously have this problem but I can't positively say
>> that I haven't
>> changed my throwing and trimming methods. I can say that the clay body a=
nd
> kiln
>> are different.
>>
>> I would appreciate any input or suggestions for trial runs to
>> figure out the
>> problem.
>>
>>
>> Thank you,
>> Daniela Rumpf
>>
Paul Haigh on wed 4 may 11
I recently solved a warping problem in my plates for a commission, though I=
may have tweaked more than one variable at once, and these changes were ov=
er 2 firings. I'm wood firing to over cone 12, so warpage is a big concern =
on plates.
-I switched to a body with a little grog
-I bisqued plates, rather than single firing. I bisqued them on edge, rathe=
r than flat, which may help your potential reduction or lower bisque temp i=
n the plate middle.
-I used a thinner wire to cut them off the batt, but left them until they w=
ere quite stiff before flipping and trimming- I had a fatter wire that woul=
d actually cause the rim to move just a bit, so I worried about memory. I c=
ut it with the wheel spinning.
-Was careful about trimming the turn at the foot of the plate to get it thi=
nned down after reading some stuff here
Paul Haigh
Wiley Hill Mudworks
Web: http://wileyhill.com
Facebook: http://www.facebook.com/pages/Wiley-Hill-Mudworks/108145139230652
etsy: http://www.etsy.com/shop/WileyHillMudworks
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