Craig Clark on thu 4 may 06
Hello all, I have recently thrown several "double walled" vessels. I
have admired them for years and decided to give the form a whirl. Well,
the throwing part went well enough, but I have now cracked two of the
in separate bisque firings. They are about 16 inch diameter, double
walled bowl shapes with nice fleshy lips. One stands about 12 inches
tall and the other was a shallower form that was a bit wider. I put a
slip texture on the outside of the first one and thougth that perhaps
the cracking was from the application of the slip a resultant uneven
drying between the outer wall and the inner wall. But the second one did
not have any slip application and it also ended up with an outer wall crack.
The clay body is one that I have used extensively and have not
experienced any type of problem with. It is a real toothy mix from
Laguna called WSO. The cracks appear only on the outer wall. Nothing on
the bottom or the inside. One of the cracks goes partially into the
lip.The bisque was what I call nice and slow. I start off with the kiln
on low for an over night and then begin bringing it up the next day
after it has reached red heat. Once the bisque has gotten to a nice
red/orange glow I rock and roll to an 04.
Does anyone on the list have any experience with successfully firing
double walled vessels? Do I need to fire even slower as if I were firing
a large sculptural form? Could the cracking be occuring on the way down,
rather than on the way up? I let the kiln cool naturally and I have not
arranged any type of slow cooling brick network around the perimeter of
the piece as I would for a large platter form. Nor am I using Vince's
infamous starburst array under the piece. Do I need to do this?
Thank you for any and all help or suggestions
Craig Dunn Clark
619 East 11 1/2 St
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
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