Mary Livingston on sun 21 mar 04
I am trying to help out a colleague who needs to fire slip cast clay =
mold pieces, both 06 bisque and cone 6 glaze. I have an electronic kiln =
sitter and need how to program it for firing these pieces. They tend to =
crack in a fast firing so I can't cone fire them. Any help would be =
appreciated. Thanks.
Snail Scott on mon 22 mar 04
At 12:43 PM 3/21/04 -0700, Mary L. wrote:
>I am trying to help out a colleague who needs to fire slip cast clay mold
pieces, both 06 bisque and cone 6 glaze. I have an electronic kiln sitter
and need how to program it for firing these pieces. They tend to crack in
a fast firing so I can't cone fire them...
Normally, slip-cast work is the simplest to fire.
Consistently thin-walled forms mean that you should
be able to fire them more quickly than most other
types of ceramic work, with fewer problems due to
firing schedule or speed. So, I question whether a
too-fast firing is really the culprit here. When I
fire slip-cast work, I generally allow an hour of
candling; after that it scarcely seems to matter
how fast I fire.
What kind of cracks are you getting? Single long
cracks, or shattered sections? Where on the pieces?
Are the ^06 and ^6 pieces similarly affected? Are
open and closed forms both affected? Are thicker
pieces more vulnerable?
Since I don't know why this is happening to you, I
can't really make a useful suggestion, except to
remind you (as I'm sure you already know) that the
lowest temperatures (while moisture is still being
removed) are the most critical to a damage-free
firing, and going extra-slow during the first few
hundred degrees is never a bad idea.
-Snail
Jon Pacini on mon 22 mar 04
Hi Mary--------- There is no reason to fire a slip cast piece any
differently than a similar size and shape thrown or hand built one. Glaze
crazing is rarely a firing fault, too fast a cooling may complicate it, but
usually this is a problem of the fit between the clay and glaze. As for
cracking, there s any number of things that can cause that, not all of them
firing related. I d need more info on the crack itself to determine when the
crack is occurring. Are they showing up in the bisque or glaze firing?? Are
they hairline cracks or wide and ragged--- is the glaze sharp edged at the
crack or is it rounded???
We ll start there and see where we go----
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: Mary Livingston [mailto:maryliv@earthlink.net]
Sent: Sunday, March 21, 2004 12:19 PM
To: Jon Pacini
Subject: Firing Slip Cast Clay
I am trying to help out a colleague who uses slip casting for his pieces and
is having trouble finding someone to properly fire his pieces. I have a
Skutt 1027 kiln with an electronic sitter whichI am new at using and have
never fired slip cast pieces. Is there a clear firing temperature process
that I can program in to fire his pieces, bisque and glaze. The fast fire,
a normal Cone 06 and 6, causes his pieces to crack and/or craze. Any help
would be appreciated.
S.E.W. on mon 22 mar 04
First of all, I am a little confused about your reference to cone 06 =
bisque and cone 6 glaze. Slip is specific to the type of firing your are =
doing. I assume you are using low fire slip, which is greenware fired to =
04 and bisque fired to 06. You can NOT use cone 6 glazes (high fire) on =
low fire slip pieces. They are not compatible. You can't fire cone 06 =
bisque to cone 6. You need to use low fire glazes which are fired to 06 =
(normally). Also, you mentioned an electronic kiln sitter. I assume you =
don't need to use cones and that you can just program it to fire to the =
cone that you enter? If this is so, just fire the glazed bisque to 06, =
not 6. They might be cracking because you are high firing the pieces. If =
you don't put a "0" before the 6, that will "fry" your piece. If you =
want to high fire, you need to buy high fire slip. As far as the fast =
fire setting, I would recommend to leave it at it's normal setting. Slip =
casting is what I do (low fire) and it really isn't necessary to slow =
down or speed up the firing process. Low fire doesn't usually need the =
slight adjustments here and there like high fire, especially if you are =
doing this for the first time. Program it to 06 and leave it on its =
normal rate and you are all set. If you are pouring the molds yourself =
and are going to fire the greenware, make sure you fire it to 04 first. =
Make sure you are using compatible glazes too. If you do use cones in =
the kiln sitter, just put the cone in the sitter and leave at normal. I =
don't have an electronic sitter so I am not familiar with them. I hope =
this helps!=20
Rachel
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