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agafdesign

What To Do With Hairline Cracks While Clay Is Drying

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agafdesign    0

I know the correct answer is "let the piece dry slowly" ( ;) ) which I do but once in a blue moon I get a hairline crack.

 

I've seen plenty of discussions here and on the web about what to do after bisque firing but none on what to do before bisque firing.

 

Is it really just a case of pushing some wet slip into the crack with a fine brush? I'm just concerned that will make the surrounding clay wet and it will then crack leading me into a never ending circle of crack repairing. :unsure:

 

Any top tips?

 

Thanks.

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ChenowethArts    461

I know the correct answer is "let the piece dry slowly" ( ;) ) which I do but once in a blue moon I get a hairline crack.

 

 

Could you give us an idea of what kind of piece? Bowl, Platter, Hand-built, Wheel-thrown?...and if there is a common pattern to when/where cracks occur?  Drying speed is definitely a huge factor in making sure that cracks don't happen.  From my own experience, the bigger issue is uneven thickness (i.e. thin walled bowls with thicker bases).

 

I agree with Mark's suggestion. Compressing the clay at the crack may save the piece.  If this is a recurring issue, however, consider sacrificing the piece by dissecting a few sections, to see if there is an underlying cause.

 

-Paul

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Benzine    610

There are a lot of things you can do, it just depends on how dry the ware is, where it's it at, etc.

 

First off, if possible, wet rehydrate the area, you are repairing, as well as some of the area beyond this. If you get the cracked area wet enough, you could possibly just use some standard slip, with a little scoring to pull the clay particles back together.

 

You could also use paper clay, in combination with the above method, which will be less likely to shrink, when it dries, minimizing the chance for it to crack again.

 

However you fix it, let it dry slowly again. An area that is rewet, the repaired, will crack again if dried quickly, sometimes even worse than before.

So the good news is that it can be repaired. The bad news is that no matter how well you do it, it might reappear during the bisque or glaze firing, especially if you fire high.

Cracks can be from structural issues, and just don't go away. It's like an old house, where you keep patching the same spot of cracked plaster. It's not the surface that's the problem, it's what is underneath.

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Pres    896

I just added a FAQ on cracks in greenware. This should help you with your quest. continue to ask your questions here, as you can not reply on the FAQ.

 

Best,

Preston

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mregecko    18

Preston,

Can you tell me where to find the FAQ on greenware cracks is located? I just can't find an FAQ section. 

 

First post in the "In the studio" forum is a list of FAQ's. It's sticky'd to always be the first post.

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agafdesign    0

Thank you all for replying.

 

The vinegar solution seems popular but how much vinegar to clay? I'm assuming this is clear vinegar - is that right?

 

The pieces I'm mainly having an issue with are made like this:

 - the clay is rolled out and then cut into shapes

 - the shapes are then joined together to make a bowl

 

Because the shapes are fairly random the joins can be at very different angles. Sometimes I do think I push one join that is already connected when I am joining another piece and this stress may be causing the issue.

 

If anyone can post their "vinegar recipe" I'll give it a try!

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Marcia is using vinegar with clay powder (good idea). I'am using vinegar pur (means the vinegar you use for cleaning, not the one you use for cooking or salad). I don't know the English name for that.

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C. Banks    4

someone just this morning sent me

a 3 min. video on vineagar, paper slip

 

*I'm guilty of not checking the front page as often as I should

 

http://mobile.ceramicartsdaily.org/ceramic-supplies/pottery-clay/superior-slip-how-to-make-a-paper-joining-slip-to-help-attachments-stay-put/

 

same video conveniently located for those who don't just skip right over to the forums

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Chilly    329

How you cut into corners can affect cracking.   My "engineer" other half calls this "crack propagation".  I cut out a Butterfly, with cut-outs.  It cracked where I'd cut into the sharp corners.   I mended it, fired it and it was fine.  Put it into a shallow box to bring home, and on arrival, it was in three pieces, cracked where the original mend was.

 

So, I made another one, slightly thicker, but this time "he" suggested I cut each inside corner firstly with a hole cutter, so I had a nice radiused edge, then used the knife to cut into the hole and not risk cutting too far into the corner.  He found me a piece of brass tube, about 3mm across, and although I preferred the sharper corners, it didn't crack while cutting/refining.  Time will tell, as it hasn't been fired yet.

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neilestrick    1,381

I throw it away and make another one. For me it's not worth the time trying to fix it knowing it may just come back in the bisque or glaze firing.

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