agafdesign Posted March 3, 2014 Report Share Posted March 3, 2014 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. Any top tips? Thanks. Link to comment Share on other sites More sharing options...
Mark C. Posted March 3, 2014 Report Share Posted March 3, 2014 I rub them out with a stick tool. Mark Link to comment Share on other sites More sharing options...
ChenowethArts Posted March 3, 2014 Report Share Posted March 3, 2014 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 Link to comment Share on other sites More sharing options...
Benzine Posted March 3, 2014 Report Share Posted March 3, 2014 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. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted March 3, 2014 Report Share Posted March 3, 2014 I mix vinegar and powdered clay body and rub it into the crack and burnish (compress). Marcia Link to comment Share on other sites More sharing options...
Pugaboo Posted March 3, 2014 Report Share Posted March 3, 2014 I do what Marcia does. Terry Link to comment Share on other sites More sharing options...
Evelyne Schoenmann Posted March 4, 2014 Report Share Posted March 4, 2014 Marcia beat me to the answer... Vinegar is the magic word when you have hairline cracks. Link to comment Share on other sites More sharing options...
Pres Posted March 4, 2014 Report Share Posted March 4, 2014 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 Link to comment Share on other sites More sharing options...
sindy1232 Posted March 4, 2014 Report Share Posted March 4, 2014 Preston, Can you tell me where to find the FAQ on greenware cracks is located? I just can't find an FAQ section. Link to comment Share on other sites More sharing options...
mregecko Posted March 4, 2014 Report Share Posted March 4, 2014 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. Link to comment Share on other sites More sharing options...
agafdesign Posted March 4, 2014 Author Report Share Posted March 4, 2014 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! Link to comment Share on other sites More sharing options...
Evelyne Schoenmann Posted March 4, 2014 Report Share Posted March 4, 2014 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. Link to comment Share on other sites More sharing options...
C. Banks Posted March 4, 2014 Report Share Posted March 4, 2014 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 Link to comment Share on other sites More sharing options...
Chilly Posted March 5, 2014 Report Share Posted March 5, 2014 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. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted March 5, 2014 Report Share Posted March 5, 2014 Recipes I have seen are just vinegar and as much clay to get the right consistency for the slip. Very easy. Never tried it though. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted March 5, 2014 Report Share Posted March 5, 2014 The mix depends on the repair needed. A thin paste for fine cracks and smooth /burnish with a rib. Marcia Link to comment Share on other sites More sharing options...
neilestrick Posted March 5, 2014 Report Share Posted March 5, 2014 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. Link to comment Share on other sites More sharing options...
Darcy Kane Posted March 8, 2014 Report Share Posted March 8, 2014 what Neil said! Link to comment Share on other sites More sharing options...
Babs Posted March 8, 2014 Report Share Posted March 8, 2014 as above, time wasted unless it's a students precious piece. Link to comment Share on other sites More sharing options...
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