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Surface cracks in bisqued paper stoneware clay


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http://www.ninawaring.com/blog/2021/8/8/help-blog-post-for-ceramic-forum

^^^^^ THIS IS THE IMAGE PAGE ^^^^^^^

 

Hello! 

I've been making work for a long time but need a bit of help on this one. I had a piece that looked weird after I"d finished it, so I added a bit of extra packing with the paper clay I was using onto almost bone dry clay.  I used slurry and hatched it and did all the right things, kept it super wet for a while as the added bit dried etc, but it might've dried out a bit too quick regardless. It has been fired over a couple of days to 1000 and the piece is very sturdy, I'm just concerned about the cracks in the neck. 
I've attached some images of the hairline cracks that have appeared and im' curious as to what people think I should do. I would usually just ignore them, paint over them with underglaze and then glaze and then fire at a temperature around 1050-1100. I take very few risks in the firings. 

My question is do people think that cracks in added clay to pieces are threatening to the over all piece and do they have remedies, or can I ignore this as there will be a difference of roughly 50-100 degrees between bisque and glaze?

Thank you! 

Nina

 

 

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Hi Nina!

Good question - perhaps some of the regular forum contributors will weigh in later.
I'd dampen the cracked area with a wet brush, then fill the cracks with slip (same clay, but without the paper), repeating if the cracks show once the dry. That said, no guarantee the cracks wouldn't re-form and/or get bigger; I've had some luck with filling cracks afore glazing and final fire, however, they were very small and not structural flaws ...yet.

fwiw, looks like a level or two bigger than hairline.

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It looks like you used too much water when you did the patch. The more water in the slip, the more it’s going to shrink. If the crack wasn’t structural before, I don’t think it will be now. But it’s only going to get larger with subsequent firings, even if it’s just a little bit. 

At this point, your clay doesn’t have the support from the paper fibres any more, so its more friable. I don’t know how vitreous your clay gets, or how much it’s going to want to move in the glaze firing. If the dog’s head has a pronounced snout instead of a more snubbed shape, would the extra weight in the front pull it forward and down? Is there glaze involved, or can you put some kind of support under the chin?

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Mad

Y be worth researching "Spooze" can be used in bisqued or raw pieces but has to be refiref before glazing if used on bisqueware.

Was your patch to mend a structural flaw or an aesthetic?

Low fire, a prop narrowing at point of contact under chin of dog, could be ground for any roughness and not be unsightly imo

What cone are you firing to?

Edited by Babs
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It was to fix an aesthetic flaw! His neck was too dainty. I think low fire and a prop is the perfect idea. I was going to fire to cone 4, between 1050 and 1100. The highest my work goes to is 1100 regardless. 

 

On 8/9/2021 at 7:47 AM, Babs said:

Mad

Y be worth researching "Spooze" can be used in bisqued or raw pieces but has to be refiref before glazing if used on bisqueware.

Was your patch to mend a structural flaw or an aesthetic?

Low fire, a prop narrowing at point of contact under chin of dog, could be ground for any roughness and not be unsightly imo

What cone are you firing to?

 

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On 8/9/2021 at 5:40 AM, Callie Beller Diesel said:

It looks like you used too much water when you did the patch. The more water in the slip, the more it’s going to shrink. If the crack wasn’t structural before, I don’t think it will be now. But it’s only going to get larger with subsequent firings, even if it’s just a little bit. 

At this point, your clay doesn’t have the support from the paper fibres any more, so its more friable. I don’t know how vitreous your clay gets, or how much it’s going to want to move in the glaze firing. If the dog’s head has a pronounced snout instead of a more snubbed shape, would the extra weight in the front pull it forward and down? Is there glaze involved, or can you put some kind of support under the chin?

There's a big super gloss glaze to go over the top once the firing is done. The prop under the head is super doable though. 

 

I didn't know about the water bit. I really appreciate the information on that one. I've sanded it back a bit more and the cracks have become far less pronounced. 

Sorry to nitpick, what does Friable mean in this context? I tried to google but nothing came up. I've done some pretty dangerous fires before with this clay and they've all come out very well. It's a pretty rock steady clay, I just think you're entirely right about the use of too much water. 

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Friable means easily crumbled. The paper fibres have fired out, so now there’s gaps where it used to be. You’ve created a more porous clay body. 

I’ve seen some people add too much pulp to their paper clay, and they accidentally created a structure that was stronger when green than when fired. But if your clay is holding up, don’t fix what isn’t broken.

 

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5 minutes ago, Callie Beller Diesel said:

Friable means easily crumbled. The paper fibres have fired out, so now there’s gaps where it used to be. You’ve created a more porous clay body. 

I’ve seen some people add too much pulp to their paper clay, and they accidentally created a structure that was stronger when green than when fired. But if your clay is holding up, don’t fix what isn’t broken.

 

thank you so much for this !! I've never asked a question on a forum before and I am overwhelmed by the amount of help you guys have given! I'm so grateful!

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