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Cracks In Wall Plaques/tiles


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#1 Malena

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Posted 21 May 2010 - 04:02 PM

Hello! I create wall plaques (like layed tiles) and I am having serious crack problems. At first, I was only having cracks in these pieces in the glaze kiln, but now I am getting cracks in the bisque kiln as well. I have tried several solutions suggested to me, but the problem still exists. The cracks are in the bottom of the pieces (side touching shelf) and sometimes will come through to the front of the piece. They mainly begin at the top of the piece and go towards the center, but not always. Some cracks are very slight, and some are pretty deep and wide.

Please advise... I have boxes of plaques with cracks and it is very disheartening to loose so many pieces.

Thank you!!

Malena

#2 Chris Campbell

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Posted 21 May 2010 - 07:06 PM

We need lots more info before we can even start.
How do you build them?
Did they ever fire just fine?
What kind of clay?
What firing temp?
What kind of firing profile?j

Chris Campbell
Contemporary Fine Colored Porcelain
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#3 Malena

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Posted 22 May 2010 - 07:34 AM

We need lots more info before we can even start.
How do you build them?
Did they ever fire just fine?
What kind of clay?
What firing temp?
What kind of firing profile?j



Thank you for your help!

I use a portable slab roller to make slabs about 3/8"thick and texture them - cut into squares about 6" x 6" or so; on top of piece slip and score a thinner textured flat piece of clay; on top of that slip and score a thinner piece of clay with my phrase or quote. On the back, I insert an inverted U-shaped piece of high-fire wire for hanging about an inch or so from the top.

I do have pieces that fire fine, I'm finding 10 - 20% of each load have these cracks. The problem is now occuring in the bisque kiln when before it was only in the glaze kiln. Cannot see the connection between the pieces that are cracking

I'm using Standard 181 - white stoneware

Bisque to 04 and glaze to 6

Not sure what you mean by firing profile... ?

Thanks again and let me know if a picture would be helpful.

#4 Chris Campbell

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Posted 22 May 2010 - 08:33 AM

It doesn't sound like you are doing anything obviously wrong.

Do you use a rolling pin across the width of the slab before using it to even out the pull?

Is iit possible the kiln shelf is warped a bit and the ones in that area are getting stressed?

Are the cracked ones always in the same spot in the kiln ... Or on the top or bottom?

Is there any difference in the wire placement on the ones that crack?

Still at a loss here ... A picture would be great!

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

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#5 Malena

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Posted 23 May 2010 - 10:22 PM

It doesn't sound like you are doing anything obviously wrong.

Do you use a rolling pin across the width of the slab before using it to even out the pull?

Is iit possible the kiln shelf is warped a bit and the ones in that area are getting stressed?

Are the cracked ones always in the same spot in the kiln ... Or on the top or bottom?

Is there any difference in the wire placement on the ones that crack?

Still at a loss here ... A picture would be great!


Attached File  Crack 1.jpg   314.2KB   25 downloadsAttached File  Crack 2.jpg   88.36KB   26 downloadsAttached File  Crack 3.jpg   40.32KB   24 downloads


No, I haven't heard about using the rolling pin to even out the pull - I will do that.

I have noticed some shelves are slightly warped - is that normal after one year of use? Do you suggest replacing them?

The cracked plaques are on all three levels of the kiln - not one in particular

The wire is in about the same spot each time - about 1.5 inch from the top

I have attached pictures - thanks again!!!

#6 Chris Campbell

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Posted 24 May 2010 - 08:16 PM

In seeing the images I suspect the crack is in the same place all the time, but you build some tiles in one direction and others crossways.

This is what I would suggest for your next production.

Roll out the slabs and then loosen the cloth and use a large rolling pin to roll across the slab at a 90 degree angle.
Loosen the slab from the cloth and let it rest a bit.

Then create the tiles with your usual method.

Try firing some of them standing up between two kiln posts ... rather than lying flat ... to see if there is any difference.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

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#7 Malena

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Posted 24 May 2010 - 10:36 PM

In seeing the images I suspect the crack is in the same place all the time, but you build some tiles in one direction and others crossways.

This is what I would suggest for your next production.

Roll out the slabs and then loosen the cloth and use a large rolling pin to roll across the slab at a 90 degree angle.
Loosen the slab from the cloth and let it rest a bit.

Then create the tiles with your usual method.

Try firing some of them standing up between two kiln posts ... rather than lying flat ... to see if there is any difference.



Thank you! I will try those tips - I appreciate your advice.

Malena

#8 Chris Campbell

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Posted 25 May 2010 - 06:35 PM

Great! Be sure to let us know what happens.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

TRY ...   FAIL ...  LEARN ...  REPEAT


#9 Malena

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Posted 28 May 2010 - 10:38 AM

Great! Be sure to let us know what happens.



Crack update! :)

I bisqued several plaques standing up as suggested, but still got some cracks - these were already constructed before the other suggestions. Sounds like it might be in the construction and not the firing (?). Next time I make plaques I will try the rolling advice... I'm looking forward to seeing what happens!

Malena

#10 Marcia Selsor

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Posted 02 July 2010 - 06:20 AM

I roll out slabs on a 30 inch slab roller and turn the direction..similar to Chris' suggestion. I dry my slabs on sheet rock with a liner of newsprint paper between the sheet rock and clay. This allows shrinkage movement. Then I wax the edges about 1-2" around the entire slab. This prevents the edges from drying too fast and prohibits warping. My slabs are as large as 25 inches.
So: rotate the slab to reduce stress...alleviate by rotating or with a rolling pin.
let it dry without sticking to the surface
dry it slowly by wrapping it, use sheetrock, and wax the edge.




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