Kenneth Dickerson on wed 9 aug 06
Hello
I have been having problems with vertical cracks in a clay body
commercially produced for raku firing. During three separate firings
from a cold start with bisque fired and dry pots, 6 out of 7 pots
have developed large vertical cracks. My burners are level with the
floor with a 9" brick up to the shelves. The firing time is about an
hour with propane. Does anyone have any ideas on what the problem
might be?
thanks, Ken
Robert W. Anderson on thu 10 aug 06
Ken,
You said 9" brick...up to the shelve. Is this a
hard brick used as a flame splitter or does it
support your shelve? If a hard brick is used as a
splitter, there should be space between it and the
shelve. If used as a shelve post they (9" hard
brick) will create cool spots on the
shelve...which will in turn may create a cooler or
stress area on the bottom of the pot. There are,
of course, many variables...bisque temperature,
clay thickness; etc. Send me a note off
line...maybe we'll solve the problem.
Bob Anderson
rwanaa@charter.net
----- Original Message -----
From: "Kenneth Dickerson"
To:
Sent: Wednesday, August 09, 2006 10:21 AM
Subject: cracks in raku clay body
> Hello
> I have been having problems with vertical
cracks in a clay body
> commercially produced for raku firing. During
three separate firings
> from a cold start with bisque fired and dry
pots, 6 out of 7 pots
> have developed large vertical cracks. My burners
are level with the
> floor with a 9" brick up to the shelves. The
firing time is about an
> hour with propane. Does anyone have any ideas on
what the problem
> might be?
>
> thanks, Ken
>
>
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Paul Gerhold on thu 10 aug 06
Ken,
Much more information needed. Is it a new body for you? Is it a new batch of
clay? A new kiln? A new shape for you? Is the cracking in front of the
burner or in back or at random? Is cracking occuring during heat up or after
cooling ?
Paul
William & Susan Schran User on thu 10 aug 06
On 8/9/06 11:21 AM, "Kenneth Dickerson" wrote:
> I have been having problems with vertical cracks in a clay body
> commercially produced for raku firing. During three separate firings
> from a cold start with bisque fired and dry pots, 6 out of 7 pots
> have developed large vertical cracks.
Please respond with more information about the forms that are cracking.
Sounds like a construction or design flaw.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Duane Archer on thu 10 aug 06
Ken, I had the same problem. Try putting a piece of room temperture old
broken shelf material under your pot before you begin firing. The heat from the
previous firing remaining in the kiln caused mine to crack and break. Too
large of differential between pot and kiln. I now use disposable discs that
are about 1/4 inch thick and 3 inches in diameter instead of the old shelf
material.
Duane
Ron Roy on fri 11 aug 06
Hi Ken,
I need to know - are the cracks happening where there is glaze? If so is
the glaze at the crack sharp or blunt?
RR
>Hello
> I have been having problems with vertical cracks in a clay body
>commercially produced for raku firing. During three separate firings
>from a cold start with bisque fired and dry pots, 6 out of 7 pots
>have developed large vertical cracks. My burners are level with the
>floor with a 9" brick up to the shelves. The firing time is about an
>hour with propane. Does anyone have any ideas on what the problem
>might be?
>
>thanks, Ken
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
marvpots@juno.com on sat 12 aug 06
Hi Ken:
Are you pre-heating your pots before putting them into the hot raku kiln=
? There are various methods of preheating: some people put the next ba=
tch on top of the hot kiln for preheating; I have my electric kiln reas=
onably close to my raku kiln and so, while the first round which is obv=
iously cold, is in the kiln, I place the second round in the electric k=
iln at LOW for just the lower two sections and thus set up a rythm, one =
load firing, one load warming, and after the first load goes into my red=
uction can, another load goes into the electric kiln and so on. No crac=
ks, no breakage, just a lot of careful attention and just light water sp=
raying when the pots come out of the reduction can.
If this is possible in your set up, try it and let me know if things imp=
rove. =
Good luck!
Marvin Flowerman
marvpots@juno.com
=
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