Jeff Lawrence on mon 30 jul 12
Hi,
Swollen with hubris, I told my wife I could make a pot (25" tall and wide)
for a house tree we've got, but no kiln gods are smiling yet. Please advise
on how to justify my bragadoccio.
The first one, sculptural white stoneware with a fair amount of tooth in
it, I bisqued first and it looked and rang sound going back in. After
glaze firing, though, the rim, about 2.5" wide, was badly cracked. In
places, it looked like it cracked on the warm-up, because the glaze
partially healed it, and other places, it looked like the first crack had
widened later, since the glaze edges were sharp both sides of the 1/8" gap.
Second one I single fired for a more interesting disaster - cracked rim
looked like some alien thing was swelling up inside it and the outside wall
shed palm-sized flakes ionto the surrounding ware.This one had less grog in
it but was more even, with about 3/4" thick walls and a rim about 1.5".
Firing schedule:
- disaster #1 - candled overnight to 400 F, 10.5 hours to temp, 15 hours or
so cooling
- disaster #2 - candled overnight to 500 F, 17 hours to temp, 20 hours
cooling
I'm thinking for the next iterations to
- mix a bunch of grog into the clay to open the body
- fire slower
Any other suggestions?
Jeff
disgruntled but determined
Jeff Lawrence on tue 31 jul 12
Thanks for the thoughts on my big pot adventure. I suspect I got
steam-punked from the tighter clay I used for #2, though I'm still puzzled
about the cracks in #1, since I bisqued it first.
My sufferings are just part of learning about massier ware but they'll be
over soon. I'm currently pugging so much filler into the clay that after
firing the next one I expect to see the roots inside through the pores .
As for building technique, it's as Lee suggested - coil-throwing. I read
about this in a John Conrad book that also had pix of Rimas and Nils, both
too busy potting to get haircuts. It's a fun exercise in any case.
Jeff
Randall Moody on tue 31 jul 12
Are you trimming a foot on them? I found that most rim cracks are due to
pressure on the rim during trimming. Especially if you are not trimming
them in a chuck. For larger pots (18" and above) I throw them so that there
is no need to trim a foot. It is easier and saves time. I just bump up the
bottom and roll the edge to finish.
Hope this helps and good luck!
On Tue, Jul 31, 2012 at 1:29 AM, Jeff Lawrence wrote:
> Hi,
>
> Swollen with hubris, I told my wife I could make a pot (25" tall and wid=
e)
> for a house tree we've got, but no kiln gods are smiling yet. Please advi=
se
> on how to justify my bragadoccio.
> The first one, sculptural white stoneware with a fair amount of tooth in
> it, I bisqued first and it looked and rang sound going back in. After
> glaze firing, though, the rim, about 2.5" wide, was badly cracked. In
> places, it looked like it cracked on the warm-up, because the glaze
> partially healed it, and other places, it looked like the first crack had
> widened later, since the glaze edges were sharp both sides of the 1/8" ga=
p.
> Second one I single fired for a more interesting disaster - cracked rim
> looked like some alien thing was swelling up inside it and the outside wa=
ll
> shed palm-sized flakes ionto the surrounding ware.This one had less grog =
in
> it but was more even, with about 3/4" thick walls and a rim about 1.5".
> Firing schedule:
> - disaster #1 - candled overnight to 400 F, 10.5 hours to temp, 15 hours =
or
> so cooling
> - disaster #2 - candled overnight to 500 F, 17 hours to temp, 20 hours
> cooling
> I'm thinking for the next iterations to
> - mix a bunch of grog into the clay to open the body
> - fire slower
> Any other suggestions?
>
> Jeff
> disgruntled but determined
>
--
Randall in Atlanta
http://wrandallmoody.com
Bonnie Hellman on tue 31 jul 12
Let the piece get fully dry before putting it in the kiln.
Bonnie
Bonnie Hellman
Ouray, CO
On Mon, Jul 30, 2012 at 11:29 PM, Jeff Lawrence wrote:
> Hi,
>
> Swollen with hubris, I told my wife I could make a pot (25" tall and wid=
e)
> for a house tree we've got, but no kiln gods are smiling yet. Please advi=
se
> on how to justify my bragadoccio.
> The first one, sculptural white stoneware with a fair amount of tooth in
> it, I bisqued first and it looked and rang sound going back in. After
> glaze firing, though, the rim, about 2.5" wide, was badly cracked. In
> places, it looked like it cracked on the warm-up, because the glaze
> partially healed it, and other places, it looked like the first crack had
> widened later, since the glaze edges were sharp both sides of the 1/8" ga=
p.
> Second one I single fired for a more interesting disaster - cracked rim
> looked like some alien thing was swelling up inside it and the outside wa=
ll
> shed palm-sized flakes ionto the surrounding ware.This one had less grog =
in
> it but was more even, with about 3/4" thick walls and a rim about 1.5".
> Firing schedule:
> - disaster #1 - candled overnight to 400 F, 10.5 hours to temp, 15 hours =
or
> so cooling
> - disaster #2 - candled overnight to 500 F, 17 hours to temp, 20 hours
> cooling
> I'm thinking for the next iterations to
> - mix a bunch of grog into the clay to open the body
> - fire slower
> Any other suggestions?
>
> Jeff
> disgruntled but determined
>
Lee on tue 31 jul 12
Jeff,
What is your throwing method? For larger things, I like
to throw the bottom and then coil throw the rest. You can even trim
the foot of the bottom before adding coils.
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
JRodgers on tue 31 jul 12
On 7/31/2012 12:29 AM, Jeff Lawrence wrote:
> the outside wall
> shed palm-sized flakes onto the surrounding ware.
Hi Jeff, long time no look.
This is classic steam shivering/flaking of the clay where the outside
surface of the pot wall heats faster than the interior of the pot wall.
Not enough to blow up the pot, but enough to blast off flakes from the
surface. Candle over night with temps not to exceed 200 degrees. Bring
the temp up to the 200 very slowly. That should do it. I have had pots
explode or shiver even though they felt perfectly dry and had been
drying for two months. The solution was to slow/low heat overnight.
Best regards,
John
Maggie Furtak on wed 1 aug 12
I'm with Bonnie and John. Sounds like a wet =3D
Hey Jeff and claybuds,=3D0A=3D0AI'm with Bonnie and John. =3DA0Sounds like =
a wet =3D
clay problem to me. =3DA0As an impatient person, I have LOTS of experience =
bl=3D
owing up wet pots. =3DA0(:=3D0A=3D0AFor my kiln, it's amazing how easily it=
will =3D
get past the boiling point of water (212 degrees F at sea level.) =3DA0This=
s=3D
houldn't be too surprising. =3DA0It's a kiln, after all, and my kitchen sto=
ve=3D
can boil a cup of water in just a few minutes. =3DA0For my kiln, I turn JU=
ST=3D
THE BOTTOM SECTION to low for an hour, and then turn it off, to candle the=
=3D
kiln. =3DA0If I turn on more than one section to low, or leave the bottom =
on=3D
low for more than an hour, it will get hotter than 212 in there, and thing=
=3D
s will explode. =3DA0For my kiln, I candle with the lid on and the peeps in=
. =3D
=3DA0The kiln stays warm like a hot summer day for a few hours after the el=
em=3D
ent has been turned off. =3DA0If I have something particularly big and thic=
k =3D
in there, I will repeat the process a few hours later. =3DA0Something truly=
g=3D
argantuan? =3DA0Heck, do it three or four times. =3DA0Takes you fifteen sec=
onds=3D
to turn the kiln on and off and potentially saves a pot that took days or =
=3D
weeks of effort. =3DA0It is worth
building the time into your schedule to give it a day or two of gentle hea=
=3D
t. =3DA0=3D0A=3D0AEvery kiln is going to be a bit different. =3DA0You'll fi=
nd what =3D
works for you. =3DA0Take notes. =3DA0Candle something. =3DA0Open the kiln a=
nd loo=3D
k at the pots on the top shelf before you start the kiln for real. =3DA0(If=
i=3D
t's too hot for you to open and check, you are candling too hot!) =3DA0Any =
bl=3D
ow-ups? =3DA0Whoops! =3DA0Candled too hot. =3DA0Checking like that can be a=
real =3D
eye-opener. =3DA0I think a lot of times, potters assume that explosions mus=
t =3D
have happened during the real heat of the firing, which actually happened i=
=3D
n the first fifteen minutes of candling (or the lack thereof.) =3DA0=3D0A=
=3D0AOr =3D
try this little experiment. =3DA0Put an inch thick wad of leather-hard clay=
i=3D
n a big bisqued bowl in an otherwise empty kiln. =3DA0The sort of thing tha=
t =3D
you would never put in the kiln, because it is CLEARLY still wet and very t=
=3D
hick, but using the bisqued bowl to protect your elements in case of explos=
=3D
ion. =3DA0Try to candle according to your usual schedule. =3DA0Check on it =
peri=3D
odically. =3DA0Did your candling schedule explode it? =3DA0Try again with l=
ess =3D
heat. =3DA0Exactly how long does it take to dry that inch thick piece of le=
at=3D
her-hard clay to what looks like a dry piece of clay? =3DA0Write it down. =
=3DA0=3D
When you think it's all the way dry, crack the clay in half. =3DA0Was it ac=
tu=3D
ally dry, all the way to the middle? =3DA0=3D0A=3D0AAnd yes, you can blow u=
p some=3D
thing which has been bisqued for exactly the same reason. =3DA0Glazing can =
su=3D
ck a heck of a lot of water into a piece, depending on the thickness of the=
=3D
piece and the glazing technique. =3DA0If I glaze, and then immediately loa=
d =3D
the kiln to fire the next morning, I do a little candle for my glaze firing=
=3D
s. =3DA0Otherwise damp glaze can blow off the piece, or a damp bisqued clay=
b=3D
ody can explode. =3DA0Believe me, if it's possible, I've done it! =3DA0=3D0=
A=3D0ATh=3D
e cost of the electricity to candle the kiln is about 2 cents. =3DA0Why ris=
k =3D
damaging the kiln, or losing work? =3DA0Build the extra time into your regu=
la=3D
r firing schedule and do it right. =3DA0The closer you are to finished with=
a=3D
piece, the more hours of work you have already put into it, and the less i=
=3D
t makes sense to rush anything. =3DA0Throw fast, trim slow, glaze methodica=
ll=3D
y and only after a full night's sleep, load the kiln like a fussy old man c=
=3D
ares for his lawn. =3DA0Slow, slower, slower-than-that... molasses-speed. =
=3DA0=3D
(:=3D0A=3D0A-Maggie=3D0A=3DA0=3D0APate Ceramics=3D0Apateceramics.etsy.com=
=3D0Apateceramic=3D
s.blogspot.com=3D0A781-956-1364=3D0A517 Fellsway East=3D0AMalden, MA 02148
Taylor Hendrix on wed 1 aug 12
Please someone post a pic of Rimas with long hair. I am skeptical.
Sent from my Droid
Taylor, in Rockport TX
wirerabbit1 on Skype (-0600 UTC)
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
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