Dan Saultman on sat 13 oct 07
Here's a great tip I would like to pass on about preventing clay
cracking while firing large thin slabs, plaques etc...
It works at all firing temperatures!
When I began firing large 20" diameter plaques, (about 1/4" thickness
or less) I was losing a serious number of of them to fundamental
cracking. Cracking all the way through the piece...lost. It turned out
that it was due to shrinkage, and the slab dragging on a dry kiln shelf
as the piece fired and contracted in the kiln. Stephanie, at Rovins
Ceramic Supply, suggested that I sprinkle a small amount of sand, just
white silica sand, on the surface of the kiln shelf, not to serve as a
cushion (which is another option), but to allow the slab to slide a
little as it contracts. It worked!
This works on bisque and final firing. The sand does not melt at all,
but remains granular like sugar, even at cone 10. If you have platters
or other large surface pieces that make contact with a kiln shelf, and
you are having cracking problems, this could help.
With a little cup, scoop out some sand and sprinkle it on your kiln
shelf. You don't need much.
Good luck,
Dan Saultman
Fine-Art Pottery
Detroit
http://www.saultman.com
Ivor and Olive Lewis on sun 14 oct 07
Dear Dan Saultman,
Always remember that free silica is a health hazard. Even coarse silica =
sand will break down and give dust. If you breath this it may lead =
eventually to silicosis.
Much better to use 100 mesh Alumina for this purpose.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Tony on sun 14 oct 07
Great tip Dan. Also works well with grog.
Just a word of caution.......make sure that the sand (or grog) doesn't fall
to the pots on the shelf below....especially for those of you with kilns
that use 2 shelves side by side.
Tony
Sydney Australia
----- Original Message -----
From: "Dan Saultman"
To:
Sent: Sunday, October 14, 2007 12:13 PM
Subject: Tip-Firing large flat work
> Here's a great tip I would like to pass on about preventing clay
> cracking while firing large thin slabs, plaques etc...
> It works at all firing temperatures!
>
> When I began firing large 20" diameter plaques, (about 1/4" thickness
> or less) I was losing a serious number of of them to fundamental
> cracking. Cracking all the way through the piece...lost. It turned out
> that it was due to shrinkage, and the slab dragging on a dry kiln shelf
> as the piece fired and contracted in the kiln. Stephanie, at Rovins
> Ceramic Supply, suggested that I sprinkle a small amount of sand, just
> white silica sand, on the surface of the kiln shelf, not to serve as a
> cushion (which is another option), but to allow the slab to slide a
> little as it contracts. It worked!
>
> This works on bisque and final firing. The sand does not melt at all,
> but remains granular like sugar, even at cone 10. If you have platters
> or other large surface pieces that make contact with a kiln shelf, and
> you are having cracking problems, this could help.
>
> With a little cup, scoop out some sand and sprinkle it on your kiln
> shelf. You don't need much.
>
> Good luck,
>
> Dan Saultman
> Fine-Art Pottery
> Detroit
> http://www.saultman.com
>
>
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WJ Seidl on sun 14 oct 07
Dan:
Others have already mentioned the risk of air-borne silica, so I won't
go there.
Might I suggest you use a shaker instead of a cup. (Any old larger
sized spice container or a cheap
1-cup aluminum screw top salt shaker from the dollar store will do)
A shaker gives you better control, avoids spillage, and the shaker top
prevents "too much" syndrome
and large lumps of clumped alumina. (Say that three times fast )
Best,
Wayne Seidl
Dan Saultman wrote:
> Here's a great tip I would like to pass on about preventing clay
> cracking while firing large thin slabs, plaques etc...
> It works at all firing temperatures!
>
> When I began firing large 20" diameter plaques, (about 1/4" thickness
> or less) I was losing a serious number of of them to fundamental
> cracking. Cracking all the way through the piece...lost. It turned out
> that it was due to shrinkage, and the slab dragging on a dry kiln shelf
> as the piece fired and contracted in the kiln. Stephanie, at Rovins
> Ceramic Supply, suggested that I sprinkle a small amount of sand, just
> white silica sand, on the surface of the kiln shelf, not to serve as a
> cushion (which is another option), but to allow the slab to slide a
> little as it contracts. It worked!
>
> This works on bisque and final firing. The sand does not melt at all,
> but remains granular like sugar, even at cone 10. If you have platters
> or other large surface pieces that make contact with a kiln shelf, and
> you are having cracking problems, this could help.
>
> With a little cup, scoop out some sand and sprinkle it on your kiln
> shelf. You don't need much.
>
> Good luck,
>
> Dan Saultman
> Fine-Art Pottery
> Detroit
> http://www.saultman.com
>
> ______________________________________________________________________________
>
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots2@visi.com
>
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