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Can someone please tell me why this tile literally cracked in an ^04 firing. The others did not. They were completely dried (3 weeks). Could this be where I joined the 2 slabs of clay? If so, how can I eliminate this problem ( joining to slabs). I used a slab roller. I appreciate any help I can get. Thank you in advance. Lindapost-63230-0-06468100-1402448255_thumb.jpg

post-63230-0-06468100-1402448255_thumb.jpg

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To much to drink?

 

kidding aside what size is this?

and why are you joining slabs?

this looks like a crack from fast cooling or firing?

mark

Yes, too much to drink! Ha!!

 

I need them to end up 12" tiles and 1/2" thick. They were flat with no warping. I did these same ones 20

years ago, but didn't use a slab roller. I made up a form and hand rolled them. I have a brand new

Paragon digital kiln and I set if on standard firing. I think I'll start with a slow fire to start and finish. The kiln was also

Almost empty and I am trying to get an actual finished size before rolling out the rest. I have 32 12" tiles with

64 triangular tiles , 32 90* bullnose and 32 specialty designed bull noses for a restaurant bar. Like

I said, I did this 20 years ago, but it needs to be refreshed. I just don't remember them breaking like this.

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I would avoid joining slabs to make a tile that large (12"). Its nice to use all of the slab, but sometimes you just have to re-wedge and re-roll. That join will be weak point, even if it is not visible to the eye. It could be the tile grabbed on some kiln wash while expanding/contracting and broke along the weak point. Or, as Mark noted, it could be cooling. But, if the tile had a seam where two slabs were joined, it has a weak point.

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I would avoid joining slabs to make a tile that large (12"). Its nice to use all of the slab, but sometimes you just have to re-wedge and re-roll. That join will be weak point, even if it is not visible to the eye. It could be the tile grabbed on some kiln wash while expanding/contracting and broke along the weak point. Or, as Mark noted, it could be cooling. But, if the tile had a seam where two slabs were joined, it has a weak point.

I stacked the tiles to fire on bisque and the top one was the only one that broke.

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Shelf looks a bit sticky   but you said that this was the top one, so i was going to write that it could have stuck at one point and so cracked when unable to move freely whilst being fired.

Top one may have heated more rapidly and cooled more rapidly being furthest from the shelf. How many in the stack?

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Make sure you have a top shelve over them closer so they cool slower especially in an empty kiln.

The shelves will keep the thermo mass cooling slower than say a large open space above them. These are large tile and need to go slow in both up and  down heat/cool cyles.

Mark

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I'll keep all of these tips in mind. The rest of the firings will be with a full kiln. I was just doing test tiles. Doing a glaze firing today and will

program to heat up and cool down slow. Thank you for all of your expert advice. I truly appreciate it. XO. Linda

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