Suzanne Wolfe on sun 23 aug 98
Does anyone have experience in firing large (20" x 23") tiles? I use an
open body formulated for cone 2. Tiles are 1/2" thick, placed on a bed of
grog. Having trouble with cracking in from the edges.
Vince Pitelka on mon 24 aug 98
>Does anyone have experience in firing large (20" x 23") tiles? I use an
>open body formulated for cone 2. Tiles are 1/2" thick, placed on a bed of
>grog. Having trouble with cracking in from the edges.
Suzanne -
This is one of the most difficult shapes to fire. Large flat forms are
always a challenge. The last thing you want to do is insulate the underside
of the tile from temperature changes, and that is exactly what the bed of
grog is doing, thus your cracking problems when the perimeter of the tile
heats or cools ahead of the center. I have fired quite a few large flat
tiles with colored clay imagery (although never as large as you are trying),
and had the best luck firing them on a network of small coils of soft clay
laid across the shelf, about two inches apart, like a series of parallel
lines. Make sure they are long enough to support the tile right to the edge
at the ends of the coils, and on the other two sides of the tile make sure
there is a coil just under the edge. This system will allow air to
circulate beneath the tile, and hopefully will allow it to heat and cool
more evenly. Along with this, you should make sure to fire very slowly,
especially below 1200 degrees F. on both the heating and cooling ramp.
Place the tile in the kiln while the network of coils is still soft, and
nestle it down slightly so that it is evenly supported overall (underall?).
Since you will be firing slowly anyway for the sake of your tile, it will
not matter that these coils are fresh clay. Good luck, and let us know how
it goes.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Bonnema on mon 24 aug 98
>----------------------------Original message----------------------------
>Does anyone have experience in firing large (20" x 23") tiles? I use an
>open body formulated for cone 2. Tiles are 1/2" thick, placed on a bed of
>grog. Having trouble with cracking in from the edges.
Hi Suzanne,
We do large tiles at cone 9/10, and have found that a very slow rate of
firing and cooling is very important. Even with that in mind we still have
some loss from cracking. Some cracks may be bisque dunting that are very
hard to see. I have taken to firing the raw tiles on edge rather than flat,
to help get them through the bisque without cracks.
Garret Bonnema
Bethel, Maine
--
Garret Bonnema
bonnema@megalink.net
Paul Lewing on tue 25 aug 98
I've never used it, but this sounds like a perfect situation for the
use of paperclay. You can make whatever clay you're already using
into paperclay. When I was at Appalachian Center for Crafts this
summer, Rosette Gault was teaching a paperclay workshop in the
adjoining studio. They were laying pclay out on these gorgeous
plaster slabs- STACKS of plaster slabs two feet square that Vince had
made for the workshop- and picking the slabs up when they were wet,
flipping them around, twisting them, and then letting them dry. No
warps, no cracks. And if one should ever happen to crack, you just
fill the crack with more pclay. It was amazing.
Paul Lewing, Seattle
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