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Massive Crack In Single Firing


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#21 timbo_heff

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Posted 29 August 2014 - 12:05 PM

You are firing to 2450 ??

With a 3 hour hold??

 

That's probably cone 14 or 15 !

 

Not that that would be the cause of your dunting but probably not a good idea



#22 JBaymore

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Posted 29 August 2014 - 02:47 PM

Looking at the photo image of the first post, you can see that the glaze surface has pulled away from the cracks that you can see.  This tells me that the cracks formed on the HEATING cycle, not the cooling side of things.  The cracks were there when the glaze started to fuse.  So this cracking happened on the front end of the firing.

 

They look like cracks that happen with raw glazing when the body is damaged by the appluication of the glaze...... cracks start forming in the body from the uneven expansion of the part of the pot where the glaze water is penetrating into the surface... and not in other areas.  Uneven thickness of the walls can exacerbate this.

 

Often you can't see them under the new layer of glaze material.... but they are there.  Then they show up in the firing.

 

Are you glazing at leather hard or bone dry?  Leather hard is the best time to do this for fewer issues.

 

best,

 

................john


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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