KAREN YUAN on wed 28 apr 04
Ron,
I'm using Cone 06-05 commercial glazes by Mayco "'Stroke & Coat Wonderglaze' for Bisque" and comparable Duncan Brand "'Concepts' Underglaze for Bisque". I will call to see if they will share the ingredients or other information. What is meant by 'low expansion'? Does the break occur in the cooling or heating phase? How is that related to 'cracking' or the opposite 'shivering'?
Thanks, Karen
Date: Tue, 27 Apr 2004 17:29:25 -0500Reply-To: Clayart Sender: Clayart From: Ron Roy Subject: Re: Glazing & Firing Saltillo TilesContent-Type: text/plain; charset="us-ascii"
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 RoyRR#415084 Little Lake RoadBrighton, OntarioCanadaK0K 1H0Phone: 613-475-9544Fax: 613-475-3513
Date: Tue, 27 Apr 2004 17:29:25 -0500Reply-To: Clayart Sender: Clayart From: Ron Roy Subject: Re: Glazing & Firing Saltillo TilesContent-Type: text/plain; charset="us-ascii"
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 RoyRR#415084 Little Lake RoadBrighton, OntarioCanadaK0K 1H0Phone: 613-475-9544Fax: 613-475-3513
Date: Tue, 27 Apr 2004 17:29:25 -0500Reply-To: Clayart Sender: Clayart From: Ron Roy Subject: Re: Glazing & Firing Saltillo TilesContent-Type: text/plain; charset="us-ascii"
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 RoyRR#415084 Little Lake RoadBrighton, OntarioCanadaK0K 1H0Phone: 613-475-9544Fax: 613-475-3513
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 RoyRR#415084 Little Lake RoadBrighton, OntarioCanadaK0K 1H0Phone: 613-475-9544Fax: 613-475-3513
---------------------------------
Do you Yahoo!?
Win a $20,000 Career Makeover at Yahoo! HotJobs
Ron Roy on thu 29 apr 04
Hi Karen,
We use the word "expansion" as a short cut. Clays and glazes expand when
heated and contract when cooled - if the expansion both clay and glaze are
close enough we have good fit. If the glaze contracts more on cooling than
the glaze we have crazing.
A glaze with a sufficiently lower contraction (during cooling) than the
body will wind up too big for the clay it is bonded to. This can crack the
clay. It can only happen after the glaze is no longer soft from heat - in
other words frozen. When this happens the edges of the glaze will be very
sharp because the glaze was already cooled and brittle.
A low expansion glaze can also chip off - sharp slivers - same problem -
look with a magnifier along the glazed edges of the tile and/or at any
sharp edges left from decoration.
I don't think you will get any information from the glaze makers - very few
of them even test their glazes for expansion.
The other possibility could be quartz dunting - this happens at 573C during
cooling - if you are bisqueing your tiles and they are not cracking then I
would not expect it to happen in the glaze firing.
RR
>I'm using Cone 06-05 commercial glazes by Mayco "'Stroke & Coat
>Wonderglaze' for Bisque" and comparable Duncan Brand "'Concepts'
>Underglaze for Bisque". I will call to see if they will share the
>ingredients or other information. What is meant by 'low expansion'? Does
>the break occur in the cooling or heating phase? How is that related to
>'cracking' or the opposite 'shivering'?
>
>Thanks, Karen
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
