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Over Glazes

Over glaze

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#1 JoLinDesigns

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Posted 04 September 2014 - 09:19 AM

Can anyone tell me why my tiles that were previously fired to ^5 would break during a ^05 firing? I added an overglaze and refired to a much lower temperature. So why would they break at this point? Very frustrating!! Is there a trick as to how to fire this last firing? Ie. different than a bisque firing? Peeps in...peeps out...slow fire/cool? I fired preprogrammed at standard rate. Should I change this? Thanks for your help. Linda

#2 neilestrick

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Posted 04 September 2014 - 09:30 AM

Many forms, especially flat ones, do not like to be refired. They don't handle the thermal shock and uneven heating very well. The top of the tile heats faster than the bottom of the tile and they crack. Try firing on stilts of some sort- even little clay coils or wads would work, or slow down the firing at the beginning and end.


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#3 oldlady

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Posted 04 September 2014 - 09:33 AM

thanks, neil, i wondered the same thing.  thought it might have to do with placement on the particular shelf in the same spot in the kiln.  shelves change shape without warping so we notice it .  have been taking pictures of the loading so i can refire in the same location if needed.


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#4 JoLinDesigns

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Posted 04 September 2014 - 10:36 AM

Thanks Nell. Makes sense. But, will I not have problems with warping if they're on stilts?

#5 Chris Campbell

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Posted 04 September 2014 - 10:47 AM

Thanks Nell. Makes sense. But, will I not have problems with warping if they're on stilts?


In my experience, no.
The clay itself should not be moving much at those low temps ... I don't think your over glaze would cause warping.
But I could be wrong as my work is mainly with porcelain.

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#6 JoLinDesigns

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Posted 04 September 2014 - 11:05 AM

Thanks Chris! Was just concerned as they are 12" x12" x1/2" tiles. Was't sure if the weight would be a factor not laying them on a flat surface.

#7 neilestrick

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Posted 04 September 2014 - 11:12 AM

 

Thanks Nell. Makes sense. But, will I not have problems with warping if they're on stilts?


In my experience, no.
The clay itself should not be moving much at those low temps ... I don't think your over glaze would cause warping.
But I could be wrong as my work is mainly with porcelain.

 

 

I'm thinking the same as Chris. A cone 6 clay should not have warping issues at low fire temps. But as always, test it first, and make sure the tile is evenly supported.


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#8 JoLinDesigns

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Posted 05 September 2014 - 12:01 PM

The stilting worked! But.... My witness cones melted on it!!! Any way to save it!




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