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Cracked Hand Built Tiles


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#1 NAS

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Posted 29 July 2010 - 09:43 AM

Good morning all,

After a 30 some year hiatus, I have returned to making ceramic sculpture. I am creating 12" x 12" x 3/4" tiles using a Bailey slab roller, which I then carve into to creat individual Bas Relief "plaques". When I first began, I was experiencing extreme warpage during all stages of the process (drying, bisque fire, and glaze fire). I have tried several clay bodied and now use a grogged cone 6 stoneware from Ceramic Supply of NY & NJ, 108G. I have reasonably controlled the warping, but now I am experiencing heavy cracks, with tiles cracking into 2 or more pieces. I have tried double rolling in 2 directions & different firing tempuratures. I know that I should handle the slabs a little as possible, but that is impossible given the nature of the forms I am trying to create. Any suggestions out there?

#2 Chris Campbell

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Posted 29 July 2010 - 09:49 AM

Can you describe what you do to them after you have rolled the slabs out?

Images of the cracked pieces would help too.

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#3 photon59

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Posted 30 July 2010 - 12:59 AM

Good morning all,

After a 30 some year hiatus, I have returned to making ceramic sculpture. I am creating 12" x 12" x 3/4" tiles using a Bailey slab roller, which I then carve into to creat individual Bas Relief "plaques". When I first began, I was experiencing extreme warpage during all stages of the process (drying, bisque fire, and glaze fire). I have tried several clay bodied and now use a grogged cone 6 stoneware from Ceramic Supply of NY & NJ, 108G. I have reasonably controlled the warping, but now I am experiencing heavy cracks, with tiles cracking into 2 or more pieces. I have tried double rolling in 2 directions & different firing tempuratures. I know that I should handle the slabs a little as possible, but that is impossible given the nature of the forms I am trying to create. Any suggestions out there?


1. It sounds like "dunting" which is especially awful when perfectly flat pieces split in firing. It seems the larger the slab, the more likely it is to happen. Some think it's because of friction on the kiln shelf. You might try a dusting of dry kiln wash under the plaque on the shelf. 2. It's important to make sure to keep them flat, since clay has a memory. If the slab bends, the distortion can pop up later, even after it has been laid flat again. i sandwich tiles between two "crezon" boards (this is sign painters board with a smooth, very slightly absorbent surface. It resists warping even with continued wetness) and flip them every few hours so they can be dried evenly top and bottom. 3. Another point is not to let them dry too quickly. I lightly cover with thin plastic, not fully opening to the air until after leather hard. Even then i flip regularly. 4. The carved areas on your pieces will dry faster and that could cause warping and/or cracking too. one thing i try to do is carve out the thicker areas from the back side to keep all areas approximately the same thickness. but sometimes it just works out and sometimes it doesn't. Posted Image hope this helps! I love bas relief.

#4 Marcia Selsor

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Posted 30 July 2010 - 02:36 AM

If they are 12 x 12 x 3/4" how much thickness variation is there after you carve in them?
I use a 30" wide Bailey and rotate the slabs. I flip them after smoothing the surface using 2 boards with clay sandwiched in between.

1. dry slowly. I dry my raku slabs 24 x 20 x 1/2" or so on paper on sheetrock and wax the edges to prevent the edges from drying too quickly and warping.
2. I bisque them standing on edge
3. if you are firing flat, make 1/4" coils ( I extrude mine) to fire your pieces of. This allows heat underneath. And helps movement during shrinkage.
4. If your bas relief has extreme thickness variation, you may have created a weak spot where two thicker areas are pulling away from each other.

Just some thoughts..

Marcia

#5 NAS

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Posted 21 August 2010 - 08:15 AM

Can you describe what you do to them after you have rolled the slabs out?

Images of the cracked pieces would help too.



Thanks for your resonse to my post. The following URL will take you to a sampling of my work.

http://s843.photobuc...Plaques%208-18/

I generally start by rolling a slab about 13/16" thick which I cut in to squares just under 12 x 12. I place them on to newsprint & then into a 12 x 12 x 3/4" form and manually re-roll them perpendicular to direction they came out of the roller. While still in the form, I rough carve the soft clay to create my reliefs. I remove the sides of the form and transfer the rough plaques to a wire shelf to begin the drying process. Once leather hard, I fine tune the forms and put them back onto the shelves to fully dry. I am using a cone 5-6 stoneware with grog and bisque to cone 02 and glaze to cone 2 or 5. The cracks appear randomly at all tempuratures.

My earlier pieces, Landscape 2807, Studies in Black & White 2802 and 2806 & Spheres 2801, warped considerably, but did not crack. I solved the warpage by drying them in open grid shelves and firing flate on individual kiln shelves. That is when the severe cracking began to appear. Studies in Black & White 2810 & 2811 were glaze fired at cone 2. Untitled 2812 & 2813 are unglazed and finished with Mason stains. they were fired to Cone 5. The rest have only been bisque fired. All are representative of similar pieces that have severely cracked into 2 or more parts. Untitled 2825 is an example, cracked horizontally.

I will begin to try some of the suggestions in the other responses to my post, but look forward to what you may have to add.

Thanks again,

NAS


Neil A Sedwin
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#6 NAS

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Posted 21 August 2010 - 08:19 AM

If they are 12 x 12 x 3/4" how much thickness variation is there after you carve in them?
I use a 30" wide Bailey and rotate the slabs. I flip them after smoothing the surface using 2 boards with clay sandwiched in between.

1. dry slowly. I dry my raku slabs 24 x 20 x 1/2" or so on paper on sheetrock and wax the edges to prevent the edges from drying too quickly and warping.
2. I bisque them standing on edge
3. if you are firing flat, make 1/4" coils ( I extrude mine) to fire your pieces of. This allows heat underneath. And helps movement during shrinkage.
4. If your bas relief has extreme thickness variation, you may have created a weak spot where two thicker areas are pulling away from each other.

Just some thoughts..

Marcia



Marcia,

Thanks for your response. I have been on vacation, but will try incorporating your comments as soon as I get back to work.

NAS

Neil A Sedwin
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#7 NAS

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Posted 21 August 2010 - 08:21 AM


Good morning all,

After a 30 some year hiatus, I have returned to making ceramic sculpture. I am creating 12" x 12" x 3/4" tiles using a Bailey slab roller, which I then carve into to creat individual Bas Relief "plaques". When I first began, I was experiencing extreme warpage during all stages of the process (drying, bisque fire, and glaze fire). I have tried several clay bodied and now use a grogged cone 6 stoneware from Ceramic Supply of NY & NJ, 108G. I have reasonably controlled the warping, but now I am experiencing heavy cracks, with tiles cracking into 2 or more pieces. I have tried double rolling in 2 directions & different firing tempuratures. I know that I should handle the slabs a little as possible, but that is impossible given the nature of the forms I am trying to create. Any suggestions out there?


1. It sounds like "dunting" which is especially awful when perfectly flat pieces split in firing. It seems the larger the slab, the more likely it is to happen. Some think it's because of friction on the kiln shelf. You might try a dusting of dry kiln wash under the plaque on the shelf. 2. It's important to make sure to keep them flat, since clay has a memory. If the slab bends, the distortion can pop up later, even after it has been laid flat again. i sandwich tiles between two "crezon" boards (this is sign painters board with a smooth, very slightly absorbent surface. It resists warping even with continued wetness) and flip them every few hours so they can be dried evenly top and bottom. 3. Another point is not to let them dry too quickly. I lightly cover with thin plastic, not fully opening to the air until after leather hard. Even then i flip regularly. 4. The carved areas on your pieces will dry faster and that could cause warping and/or cracking too. one thing i try to do is carve out the thicker areas from the back side to keep all areas approximately the same thickness. but sometimes it just works out and sometimes it doesn't. Posted Image hope this helps! I love bas relief.



Thanks for the suggestions. I have been on vacation, but I will try applying them as soon as I get back to work.

NAS




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