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Cracked Bottoms In Drying Process


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#1 Cyndi

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Posted 26 April 2010 - 02:02 AM

Hello, I am very new to this experience and don't quite know how to state things w/out getting too wordy:( But really need help w/an ongoing problem. My pieces keep cracking in the drying process. The latest are three slab bottoms to sculpture pieces. One is a planter box 14x10x9". I rolled out bottom slab approx. 1/2" thick, then the walls and let them get leather hard and attached , slipping and scoring w/magic water. When formed up I added a rope coil around corners and rim of box. I reinforced inside w/a small coil also. I formed it up on one table on a towel then after a day moved it to another to texturize. After a couple of drying days I moved it onto a thin board then onto my wire drying racks. All the time keeping it covered w/plastic bag to dry slowly. When I was moving it to wire rack I then noticed the bottom had cracked. It was leather hard at this point. Did I move it too soon from one table to the next or too many times in the process. Another piece I was working on but did not move at all was a bird bath/feeder. It too had a slab bottom around 17" in diameter w/ walls going up around 12". Another piece is a tea set try 14" in diameter. All were rolled out w/a heavy marble rolling pin, 1/2" thick. I use only Cone 5 clay. This is my most frustrating ongoing problem w/a lot of my pieces - vases, mugs, dishes, etc. small or large. Any suggestions will be greatly appreciated. P.S. Am sooooo enjoying and benefiting from the forum. Cyndi



#2 venetiancat

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Posted 23 May 2010 - 08:09 PM

Hi Cyndi,
I just noticed your post, haven't been on for a while.
This happened to me in the beginning too, so I FEEL your PAIN!.:( What is happening is that the outside walls are drying faster than the inside, and the difference in shrinkage is causing the cracking on the bottom. You want the middle to dry before the outer walls do.

Try drying your wares with plastic on the outer walls and rim only,exposing the center/bottom to the air. You sort of make a donut of plastic. Then, once the middle starts to dry, remove the plastic. I found also that drying my pieces on plaster bats or wooden boards (plaster works best for me) rather than wire racks helps a great deal.

Hope this helps, let me know how you make out.:)
Julia
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Venetian Cat Studio Historical Reproduction Pottery and Fine Art
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#3 Cyndi

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Posted 23 May 2010 - 09:47 PM

Hi Cyndi,
I just noticed your post, haven't been on for a while.
This happened to me in the beginning too, so I FEEL your PAIN!.Posted Image What is happening is that the outside walls are drying faster than the inside, and the difference in shrinkage is causing the cracking on the bottom. You want the middle to dry before the outer walls do.

Try drying your wares with plastic on the outer walls and rim only,exposing the center/bottom to the air. You sort of make a donut of plastic. Then, once the middle starts to dry, remove the plastic. I found also that drying my pieces on plaster bats or wooden boards (plaster works best for me) rather than wire racks helps a great deal.

Hope this helps, let me know how you make out.Posted Image
Julia



#4 Cyndi

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Posted 23 May 2010 - 09:52 PM

Thanks Julia,
It's nice to get a reply, even a late one:))) I actually sought help elsewhere since noone responded and was told exactly what you told me so thanks again. I am also experimenting w/paper clay. I read it doesn't crack like in the usual drying process. Sure is a mess tho and does stink, but so far it is working. Haven't fired any yet. Hope I'm not disappointed. Just made a 36" bird bath in form of a tree. We'll see:) Cyndi



#5 venetiancat

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Posted 24 May 2010 - 09:58 AM

Thanks Julia,
It's nice to get a reply, even a late one:))) I actually sought help elsewhere since noone responded and was told exactly what you told me so thanks again. I am also experimenting w/paper clay. I read it doesn't crack like in the usual drying process. Sure is a mess tho and does stink, but so far it is working. Haven't fired any yet. Hope I'm not disappointed. Just made a 36" bird bath in form of a tree. We'll see:) Cyndi


Good luck with the paper clay Cyndi:). Another thing that helps greatly with S-cracks in thrown pieces is when throwing, push the clay along the bottom in towards the middle, out again, and back in. This will align the particles.

Best,
Julia
Julia Passamonti-Colamartino
Venetian Cat Studio Historical Reproduction Pottery and Fine Art
venetiancat.com
"Once I learned to herd cats, I realized that anything is possible!"

#6 clay lover

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Posted 26 May 2010 - 12:30 PM


Thanks Julia,
It's nice to get a reply, even a late one:))) I actually sought help elsewhere since noone responded and was told exactly what you told me so thanks again. I am also experimenting w/paper clay. I read it doesn't crack like in the usual drying process. Sure is a mess tho and does stink, but so far it is working. Haven't fired any yet. Hope I'm not disappointed. Just made a 36" bird bath in form of a tree. We'll see:) Cyndi


Good luck with the paper clay Cyndi:). Another thing that helps greatly with S-cracks in thrown pieces is when throwing, push the clay along the bottom in towards the middle, out again, and back in. This will align the particels.

Best,
Julia



#7 clay lover

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Posted 26 May 2010 - 12:34 PM



Thanks Julia,
It's nice to get a reply, even a late one:))) I actually sought help elsewhere since noone responded and was told exactly what you told me so thanks again. I am also experimenting w/paper clay. I read it doesn't crack like in the usual drying process. Sure is a mess tho and does stink, but so far it is working. Haven't fired any yet. Hope I'm not disappointed. Just made a 36" bird bath in form of a tree. We'll see:) Cyndi


Good luck with the paper clay Cyndi:). Another thing that helps greatly with S-cracks in thrown pieces is when throwing, push the clay along the bottom in towards the middle, out again, and back in. This will align the particels.

Best,
Julia


Sorry, I haven't been on or I would have replied. I expect the even drying is the problem, it doesn't matter how slowly you dry if it is still uneven, the do-nut of plastic is a good idea. Other thing I thought of, are you rolling the clay slab in different directions, and even turning it over to roll out? Sometime that can help prevent cracks, the clay shrinks in several directions that way, due to clay memory.



#8 seedy45

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Posted 28 May 2010 - 03:37 PM

Thanks Julia,
It's nice to get a reply, even a late one:))) I actually sought help elsewhere since noone responded and was told exactly what you told me so thanks again. I am also experimenting w/paper clay. I read it doesn't crack like in the usual drying process. Sure is a mess tho and does stink, but so far it is working. Haven't fired any yet. Hope I'm not disappointed. Just made a 36" bird bath in form of a tree. We'll see:) Cyndi




Just a note about paper clay... If you make it like I do (w/ cheap toilet paper) it is predisposed to mold. I have overcome this by adding some white vinegar. Vinegar is good to use when joining clay anyway and it raises the ph enough to reduce mold growth... but if you leave it too long it will mold anyway... I make smaller batches.




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