Carolyn C. White on sun 6 jul 08
I have an acquaintance who "glaze paints" her art on commercially
manufactured Mexican paving tiles. She paints images on the tiles using
commercially prepared low fire glazes, and then fires the tiles to cone 06
in an electric kiln, with a kiln sitter. I was at her studio last weekend
for a studio sale she was having, and noticed a large number of 12x12 tiles
in the "seconds corner" had cracked all the way through, and I asked her how
much breakage she was having - she said about 1 in 3 of these large tiles
broke.
I couldn't think of anything in her process that could be causing the
breakage except perhaps that the back of the tiles have ridges (presumably
to aid in adherence to mortar), and that this might be causing some "drag"
when the pieces are shrinking during the firing. She told me that she now
lays the tiles on a bed of sand on the kiln shelf when firing and this has
helped reduce the breakage somewhat. I'm wondering if anyone else has any
suggestions as to what might be causing the cracking. It occurred to me
that perhaps rapid cooling could be an issue?
The images she paints on the tiles are usually fairly detailed/intricate
(and therefore time consuming) so it seems a real shame that she is losing
so much work to cracking. (For samples of her work (which I think is
exceptional) her website is: http://www.artontile.com
. Any thoughts or suggestions would be welcome.
Thanks.
Carolyn Caldwell-White
Fairfax, CA
Ron Roy on thu 10 jul 08
Hi Carolyn,
Sounds like cooling cracking to me - if that is it - it happens at 573C on
the way down. Probably a lot of silica in those tiles and the quartz -
going through it's inversion with a volume change during cooling is the
cause.
Ask her if it happens more in the bottom half of the kiln.
Either slow the cooling during the crucial period or raise the tiles off
the kiln shelves a little so they cool more evenly.
RR
>I have an acquaintance who "glaze paints" her art on commercially
>manufactured Mexican paving tiles. She paints images on the tiles using
>commercially prepared low fire glazes, and then fires the tiles to cone 06
>in an electric kiln, with a kiln sitter. I was at her studio last weekend
>for a studio sale she was having, and noticed a large number of 12x12 tiles
>in the "seconds corner" had cracked all the way through, and I asked her how
>much breakage she was having - she said about 1 in 3 of these large tiles
>broke.
>
>
>
>I couldn't think of anything in her process that could be causing the
>breakage except perhaps that the back of the tiles have ridges (presumably
>to aid in adherence to mortar), and that this might be causing some "drag"
>when the pieces are shrinking during the firing. She told me that she now
>lays the tiles on a bed of sand on the kiln shelf when firing and this has
>helped reduce the breakage somewhat. I'm wondering if anyone else has any
>suggestions as to what might be causing the cracking. It occurred to me
>that perhaps rapid cooling could be an issue?
>
>
>
>The images she paints on the tiles are usually fairly detailed/intricate
>(and therefore time consuming) so it seems a real shame that she is losing
>so much work to cracking. (For samples of her work (which I think is
>exceptional) her website is: http://www.artontile.com
> . Any thoughts or suggestions would be welcome.
>
>
>
>Thanks.
>
>Carolyn Caldwell-White
>
>Fairfax, CA
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Nancy Guido on thu 10 jul 08
Hi Carolyn,
I have made large tiles for years. I have learned by hard lessons that I don't put the 12" tiles on the bottom shelf. I put the tile entirely on the shelf, absolutely no corners hanging off. Whatever fits, fits and smaller stuff can go around the big tile. I use 3" posts over the tiles. This has worked for me at cone 6 as well as 05. I did a job with commercial tiles and low fire majolica glazes. I used 12" tiles from Home Depot. Same procedure. I fire slow.
My kiln had the extra insulation and since I was only firing tiles, it was a pretty tightly packed kiln with 3" posts all the way up. The cooling was naturally slow.
nancy g.
Susan Fox Hirschmann on thu 10 jul 08
In a message dated 7/10/2008 1:40:53 PM Eastern Daylight Time,
nguido0821@COMCAST.NET writes:
Hi Carolyn,
I have made large tiles for years. I have learned by hard lessons that I
don't put the 12" tiles on the bottom shelf. I put the tile entirely on the
shelf, absolutely no corners hanging off. Whatever fits, fits and smaller stuff
can go around the big tile. I use 3" posts over the tiles. This has worked
for me at cone 6 as well as 05. I did a job with commercial tiles and low fire
majolica glazes. I used 12" tiles from Home Depot. Same procedure. I fire
slow.
My kiln had the extra insulation and since I was only firing tiles, it was a
pretty tightly packed kiln with 3" posts all the way up. The cooling was
naturally slow.
nancy g.
Slow firing and firing on alumina hydrate works great! That way if there is
even a spec of glaze on the back the tile will still shrink and move over the
alumina hydrate.
Best of luck
Susan
When I did a large installation on porcelain tiles I fired 80 degress an hour
with a slow cooling to ^6.
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Nancy Guido on sat 12 jul 08
Jo,
The Home Depot tiles were glazed and I was using the low fire Amaco Majolica glazes. It was a commission for a school, names on tiles blah, blah, blah - last commission, won't do anymore.
But, for the Majolica to work, the tiles needed to be pre-glazed.
nancy g.
in the land of Home Depot's on every other corner - if not then it's a Lowe's
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