Karen Yuan on tue 27 apr 04
Cracking! I am losing 30 - 40 % of my 12 x 12 mexican saltillo tiles in the firing process. Many of the broken pieces are up to 3 inches apart from each other because of the force of the break. This suggests air pockets, but, as you can see below, I have resorted to some pretty slow fireing schedules. Location in the kiln & type of shelf (full or split) do not seem to be a factor. I even did a rating of how warped the tiles were prior to firing on a scale of 0 to 3. Warpage does not seem to be a factor. However, even the "flat" tiles are bowed up in the center somewhat. This makes me think that the center of the tile may drop & cause a crack. (?)
Using the kilnmaster I have done some very slow firings; the most recent was 50 deg/hr to 250 deg; them 80/hr to 600 deg; 150/hr to 1000; and so on to 1816 or a hot cone 06. It seems I've cracked just a many tiles with pretty slow firing as with the Automatic Cone Fire Slow schedule. I have not worried about the cooling process though this most recent was not rushed. Still, since I employ a kiln vent cooling may not be slow enough. I have placed a little sand under the edges of the tiles to ensure that they are not dragging.
I'm using low fire commercial Duncan & Mayco glazes.
I was told that a broken tile with a sharp edge suggests a break during cooling and a rounded edge suggest a break during firing...heating. My edges are sharp.
A Mexican manufacturer said fire for 24 hours & cool for 3 days.
My next test will be slow as above with sand supporting the entire tile...supporting the bowed area. And I will turn off the kiln vent at 800 deg (not earlier because of vent damage concerns).
Any feedback or suggestions are greatly appreciated. My stove backsplash is naked.
Karen
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Ron Roy on tue 27 apr 04
Hi Karen,
Sounds like it could be a low expansion glaze problem.
If you send me the glaze recipe I can be more sure about that.
RR
>Cracking! I am losing 30 - 40 % of my 12 x 12 mexican saltillo tiles in
>the firing process. Many of the broken pieces are up to 3 inches apart
>from each other because of the force of the break. This suggests air
>pockets, but, as you can see below, I have resorted to some pretty slow
>fireing schedules. Location in the kiln & type of shelf (full or split) do
>not seem to be a factor. I even did a rating of how warped the tiles were
>prior to firing on a scale of 0 to 3. Warpage does not seem to be a
>factor. However, even the "flat" tiles are bowed up in the center
>somewhat. This makes me think that the center of the tile may drop & cause
>a crack. (?)
>
>Using the kilnmaster I have done some very slow firings; the most recent
>was 50 deg/hr to 250 deg; them 80/hr to 600 deg; 150/hr to 1000; and so on
>to 1816 or a hot cone 06. It seems I've cracked just a many tiles with
>pretty slow firing as with the Automatic Cone Fire Slow schedule. I have
>not worried about the cooling process though this most recent was not
>rushed. Still, since I employ a kiln vent cooling may not be slow enough.
>I have placed a little sand under the edges of the tiles to ensure that
>they are not dragging.
>I'm using low fire commercial Duncan & Mayco glazes.
>I was told that a broken tile with a sharp edge suggests a break during
>cooling and a rounded edge suggest a break during firing...heating. My
>edges are sharp.
>A Mexican manufacturer said fire for 24 hours & cool for 3 days.
>My next test will be slow as above with sand supporting the entire
>tile...supporting the bowed area. And I will turn off the kiln vent at
>800 deg (not earlier because of vent damage concerns).
>Any feedback or suggestions are greatly appreciated. My stove backsplash
>is naked.
>Karen
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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