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buckeye

warped bowls

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Lately I have been having trouble with bowls warping. I think I might have a clue why but I am up for suggestions and if I am correct would be nice to have it confirmed. After throwing I cut them off the bat, leave sit for a few hours to set up then I re-cut them and flip them over.. very careful not to push in on the sides. Several hours later they are ready to trim and when I look at them they are warped. The only thing I can think of is they are drying to fast. I have noticed since late fall the air seems dryer and everything is drying quicker... doesnt really make sense to me why drying faster they would warp but its the only thing I can come up with... any suggestion would be helpful.

 

I am using a stoneware clay.. everything is drying so quick that if I throw bowls in the morning they are trimmed and done by evening.

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Buckeye;

You are moving too fast, buddy. I throw my bowls on batts. I cover the entire session with a large sheet of plastic.The next day I flip them with another batt on the rim. I trim the afternoon of the second day. Check out your batts and your ware boards. Sometimes ware boards warp if they are lumber and not plywood.Try it and see.

TJR

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Hi buckeye, welcome to the world of drying clay.

 

I agree with TJR, slow it down. low humidity dries pots to fast, drafts can also cause warping by drying one side of the bowl faster than the other. Some clays can handle fast drying more than others, but in general, slow is good.

 

I'm a hand builder and find a drying cabinet very use full. I made one by enclosing the top part of a plastic shelving unit, that has vented shelves, with a sheet of heavy plastic using duct tape, and leaving a flap on front.

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Hi buckeye, welcome to the world of drying clay.

 

I agree with TJR, slow it down. low humidity dries pots to fast, drafts can also cause warping by drying one side of the bowl faster than the other. Some clays can handle fast drying more than others, but in general, slow is good.

 

I'm a hand builder and find a drying cabinet very use full. I made one by enclosing the top part of a plastic shelving unit, that has vented shelves, with a sheet of heavy plastic using duct tape, and leaving a flap on front.

 

 

 

Matt, what source of heat do you use in your drying cabinet?

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Lately I have been having trouble with bowls warping. I think I might have a clue why but I am up for suggestions and if I am correct would be nice to have it confirmed. After throwing I cut them off the bat, leave sit for a few hours to set up then I re-cut them and flip them over.. very careful not to push in on the sides. Several hours later they are ready to trim and when I look at them they are warped. The only thing I can think of is they are drying to fast. I have noticed since late fall the air seems dryer and everything is drying quicker... doesnt really make sense to me why drying faster they would warp but its the only thing I can come up with... any suggestion would be helpful.

 

I am using a stoneware clay.. everything is drying so quick that if I throw bowls in the morning they are trimmed and done by evening.

 

 

All of the other information in the other posts is very relevant to your problem. I would definitely turn the bowl over by using another bat on it. I have also found a little trick that seems to help when moving and drying a wet bowl. I take a square of thin paper and place it evenly over the rim, smooth down lightly and then move the bowl. I often throw bowls on the wheel head, and remove them as thrown, as I am often throwing off of the hump around 20#. This trick will allow me to move the larger thinner bowls without warping them. This also helps the bowl to dry a little more evenly.

Jo-Ann likes this

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Hi buckeye, welcome to the world of drying clay.

 

I agree with TJR, slow it down. low humidity dries pots to fast, drafts can also cause warping by drying one side of the bowl faster than the other. Some clays can handle fast drying more than others, but in general, slow is good.

 

I'm a hand builder and find a drying cabinet very use full. I made one by enclosing the top part of a plastic shelving unit, that has vented shelves, with a sheet of heavy plastic using duct tape, and leaving a flap on front.

 

 

 

Matt, what source of heat do you use in your drying cabinet?

 

 

Sorry Joanie, I should say slow drying cabinet, no heat involved. It just keeps drafts off the pots and slows down water evaporation from the clay.

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Hi buckeye, welcome to the world of drying clay.

 

I agree with TJR, slow it down. low humidity dries pots to fast, drafts can also cause warping by drying one side of the bowl faster than the other. Some clays can handle fast drying more than others, but in general, slow is good.

 

I'm a hand builder and find a drying cabinet very use full. I made one by enclosing the top part of a plastic shelving unit, that has vented shelves, with a sheet of heavy plastic using duct tape, and leaving a flap on front.

 

 

 

Matt, what source of heat do you use in your drying cabinet?

 

 

Sorry Joanie, I should say slow drying cabinet, no heat involved. It just keeps drafts off the pots and slows down water evaporation from the clay.

 

 

 

Thanks, Matt.

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Hi Buckeye,

 

I agree with everyone else as that your pots are drying too quickly. After finishing an item on the wheel, I wire off, and let it sit open air for an hour or two, then cover with plastic until the next morning. Then I flip it upside down onto a ware board and all it to sit open air for an hour or two, recover and check later on that night before thinking of trimming/turning. After all is said and done, and I'm ready for to allow the piece to fully dry I set it upside down on a slotted shelf to allow for even air flow. The only time I've had any trouble with something warping is if I've had a little assistant, my grand daughter or one of my pups!

 

Hope that one of the suggestions helps with your quick drying problem.

 

Jeri Lynne

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cant believe how many posts this got so quickly! thanks everyone, I figured that was the problem and thank you for all the great suggestions.. I am going to sloooow they dry down.

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I'm at the other end of go slow-working with porcelain in our moist climate I'm always trying to dry quicker .As soon as the lips of bowl are dry enough -I'll put a bat on the top and flip them.That way the bottom catches up. Some days/sunny I can trim them same day they are thrown-most often its the next day. The sooner the bowl gets batted and flipped the better for me.

This is for all larger bowls the small ones I just flip as soon as I can by hand many to a large bat when the lips are just dry enough.

If I want to slow it down I use light plastic like the dry cleaners use or from fruit boxes from the market to cover for one night

Mark

 

I tend to think that you have uneven drying going on-what's your heat source?

Edited by Mark C.

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Lately I have been having trouble with bowls warping. I think I might have a clue why but I am up for suggestions and if I am correct would be nice to have it confirmed. After throwing I cut them off the bat, leave sit for a few hours to set up then I re-cut them and flip them over.. very careful not to push in on the sides. Several hours later they are ready to trim and when I look at them they are warped. The only thing I can think of is they are drying to fast. I have noticed since late fall the air seems dryer and everything is drying quicker... doesnt really make sense to me why drying faster they would warp but its the only thing I can come up with... any suggestion would be helpful.

 

I am using a stoneware clay.. everything is drying so quick that if I throw bowls in the morning they are trimmed and done by evening.

 

 

 

I have had the same problem in the past and have started covering all my thrown or handbuilt work with pieces of cloth (old sheets torn into manageable pieces). I found that this tended to keep moisture wicking at an even pace from my work and really reduced the warping. If I had tcover the pieces overnight, I put plastic over the cloth which kept the condensation from sitting right on the clay. Worked for me in our dry air.

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Lately I have been having trouble with bowls warping. I think I might have a clue why but I am up for suggestions and if I am correct would be nice to have it confirmed. After throwing I cut them off the bat, leave sit for a few hours to set up then I re-cut them and flip them over.. very careful not to push in on the sides. Several hours later they are ready to trim and when I look at them they are warped. The only thing I can think of is they are drying to fast. I have noticed since late fall the air seems dryer and everything is drying quicker... doesnt really make sense to me why drying faster they would warp but its the only thing I can come up with... any suggestion would be helpful.

 

I am using a stoneware clay.. everything is drying so quick that if I throw bowls in the morning they are trimmed and done by evening.

 

 

All of the other information in the other posts is very relevant to your problem. I would definitely turn the bowl over by using another bat on it. I have also found a little trick that seems to help when moving and drying a wet bowl. I take a square of thin paper and place it evenly over the rim, smooth down lightly and then move the bowl. I often throw bowls on the wheel head, and remove them as thrown, as I am often throwing off of the hump around 20#. This trick will allow me to move the larger thinner bowls without warping them. This also helps the bowl to dry a little more evenly.

 

 

I just want to make sure I understand you correctly.. throwing from the hump, before you remove the bowl from the hump you put a piece of paper on the top, smooth it down slightly to the rim then remove and it keeps it round while you are moving it? If so I HAVE to try that! If I have that right, are you then sitting a bat on top of it and leaving it sit upside down?

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Lately I have been having trouble with bowls warping. I think I might have a clue why but I am up for suggestions and if I am correct would be nice to have it confirmed. After throwing I cut them off the bat, leave sit for a few hours to set up then I re-cut them and flip them over.. very careful not to push in on the sides. Several hours later they are ready to trim and when I look at them they are warped. The only thing I can think of is they are drying to fast. I have noticed since late fall the air seems dryer and everything is drying quicker... doesnt really make sense to me why drying faster they would warp but its the only thing I can come up with... any suggestion would be helpful.

 

I am using a stoneware clay.. everything is drying so quick that if I throw bowls in the morning they are trimmed and done by evening.

 

 

All of the other information in the other posts is very relevant to your problem. I would definitely turn the bowl over by using another bat on it. I have also found a little trick that seems to help when moving and drying a wet bowl. I take a square of thin paper and place it evenly over the rim, smooth down lightly and then move the bowl. I often throw bowls on the wheel head, and remove them as thrown, as I am often throwing off of the hump around 20#. This trick will allow me to move the larger thinner bowls without warping them. This also helps the bowl to dry a little more evenly.

 

 

I just want to make sure I understand you correctly.. throwing from the hump, before you remove the bowl from the hump you put a piece of paper on the top, smooth it down slightly to the rim then remove and it keeps it round while you are moving it? If so I HAVE to try that! If I have that right, are you then sitting a bat on top of it and leaving it sit upside down?

 

 

I set it on a bat right side up, let the rim get firm, then put a bat on top of the rim and flip the two bats with bowl between to turn it upside down. Let the base get to trimming stage, and trim. Paper gets removed just before trimming. Throwing off the hump can be problematic for beginners. The problem with compression of the base and the resulting "S" shaped crack can be really tough in the beginning. Over time you improve you compression so that you don't have the problem, but it is harder to get rid of the "S" shaped crack when working off the hump.

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I'm not convinced that it's the speed of the drying. I dry porcelain pots that quickly all the time, without any trouble. I think the culprit may be uneven drying. If there is a heat source, or wind source (fan, heater, etc) in your studio that is coming from one side of the studio, then your pots won't dry evenly, and cause warping. The evenness of the pots will also have a role in how well they hold shape in drying. If the bottom is very thick compared to the rim, you'll get more warping. You can dry pots as fast as you want as long as they dry evenly.

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Hi Buck,

I use spann rings. I will try and remember tomorrow to take images of the ones I use. It is basically a circle of plaster that is tapered to a centre point. You can either place your bowl/mug rim down on it, or if it is a thinned out spann ring, you can place it on the vessel that is standing on it's footpath. I will wiggle the piece a few times during the day to ensure that it does not stick to the ring, but normally it just slides on the plaster ring as it shrinks, while it maintain it's round shape.

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hi Buckeye (and everyone else!)

Here is the long promised image or my spann rings. I have a lot of different sizes, and obviously use them according to the size of the greenware diameter. If you have any questions about them, please feel free to ask. I will help where possible :-)

post-7071-132949222511_thumb.jpg

post-7071-132949222511_thumb.jpg

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I'm not convinced that it's the speed of the drying. I dry porcelain pots that quickly all the time, without any trouble. I think the culprit may be uneven drying. If there is a heat source, or wind source (fan, heater, etc) in your studio that is coming from one side of the studio, then your pots won't dry evenly, and cause warping. The evenness of the pots will also have a role in how well they hold shape in drying. If the bottom is very thick compared to the rim, you'll get more warping. You can dry pots as fast as you want as long as they dry evenly.

 

 

I'm right there with Neil on this one. More likely uneven drying than fast drying. I have fast dried all sorts of clay bodies, both US commercial ones, as well as my own claybody formulations, and also ones from when working in Japan with numerous of their clay bodies....... and have not found warping to typically come from "fast" drying.

 

Or as was already mentioned, it could be from a ware board that is not actually flat (or one that changes shape when it absorbs moisture from the pot).

 

 

As a side note, one clay body I used while working in Japan would seriously self-destruct in about 5 minutes (massive...... and I mean massive.... cracking) if you put a close to leather-hard pot direcdtly into the sunshine to dry....... which is usually a great technique to use for so many clay bodies. Repeated testing of this with all manner of forms proved it completely.

 

Another body I used in Japan would self-destruct (cracking again) if you covered it with plastic overnight to retard drying. The slight condensation on the inside of the plastic hitting the clay surface got re-absorbed in localized areas... and "bingo"....gone!!!! Had to use layers of opened newspapers to place over the forms....... it retarded the drying and let the moisture slowly breathe through the paper's pores.

 

 

I rarely use bats, even for most dinner sized plates and small to medium bowls. (Big platters and something like a 24" diameter at the rim bowl... well yes.... bats are for sure used wink.gif .) I just pick them up off the wheelhead. And I throw a lot of smaller things off the hump and pick them off "spinning". If I chose the pieces to be "round" there does not seem to be an issue from the "wet handling". If they are slightly off round, a tiny pat or two at the correct time (not when fresh thrown) takes care of that.

 

And frequently those fresh thrown forms head right out of the studio door and into the graveled kiln yard and into the sun and wind to start to dry for eventual trimming or finishing. When they are trimmed/finished, they also then often go back outside into the wind/sun to dry from leatherhard to bone dry...... before the bisque (although many are stacked in the wood lkiln yakishime... and do not get bisqued). Good clay bodies.

 

A lot of times the issues are claybody issues too....... and not how YOU are handling the pieces. Just because a clay body comes from a "supplier" does not mean it is necessarily a GOOD claybody and the supplier actually has a strong technical background in clay body development. In this country (USA), to be a "ceramic materials supplier company" does not require any certifications or specific training.... just a "shingle" hanging outside the door. I've tried some commercial bodies that are not all that great.

 

 

best,

 

..............john

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All this information about not slowing down the drying is interesting. The conversation (and I definitely don’t question John and Neil's experience) is about wheel thrown items, which I know was the original question, most my experience with drying clay is with slab work.

 

A lot of the items I make are made from tile molds, and assembled on a form, example below

 

During the summer I really don't have that much of a problem with warping and can place work on a shelf and let it dry at it's own rate, but in the middle of winter, when the humidity is 25-35%, I have found that, for example this tree vase, would dry out of square, and the feet would become to uneven, so I started putting them in the drying cabinet I mentioned with a hole on the top to adjust the drying rate, it takes roughly 8-10 hours to reach the leather hard state, then I take it out and place it on an open shelf. This always seems to alleviate the problem. On the other hand, some flat pieces I can set on a open shelf and let dry, even in winter, with no problems.

post-8487-132952408755_thumb.jpg

post-8487-132952408755_thumb.jpg

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John said

(And frequently those fresh thrown forms head right out of the studio door and into the graveled kiln yard and into the sun and wind to start to dry for eventual trimming or finishing. When they are trimmed/finished, they also then often go back outside into the wind/sun to dry from leatherhard to bone dry.)

This what we do 5 to 6 months out of the year here-when the shop heater is not needed.May thru Sept into Oct-†he washer in photo by chimmy is for clay clothes/towels only

I keep them out of house laundry system

Mark

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I'm not convinced that it's the speed of the drying. I dry porcelain pots that quickly all the time, without any trouble. I think the culprit may be uneven drying. If there is a heat source, or wind source (fan, heater, etc) in your studio that is coming from one side of the studio, then your pots won't dry evenly, and cause warping. The evenness of the pots will also have a role in how well they hold shape in drying. If the bottom is very thick compared to the rim, you'll get more warping. You can dry pots as fast as you want as long as they dry evenly.

 

 

I'm right there with Neil on this one. More likely uneven drying than fast drying. I have fast dried all sorts of clay bodies, both US commercial ones, as well as my own claybody formulations, and also ones from when working in Japan with numerous of their clay bodies....... and have not found warping to typically come from "fast" drying.

 

Or as was already mentioned, it could be from a ware board that is not actually flat (or one that changes shape when it absorbs moisture from the pot).

 

 

As a side note, one clay body I used while working in Japan would seriously self-destruct in about 5 minutes (massive...... and I mean massive.... cracking) if you put a close to leather-hard pot direcdtly into the sunshine to dry....... which is usually a great technique to use for so many clay bodies. Repeated testing of this with all manner of forms proved it completely.

 

Another body I used in Japan would self-destruct (cracking again) if you covered it with plastic overnight to retard drying. The slight condensation on the inside of the plastic hitting the clay surface got re-absorbed in localized areas... and "bingo"....gone!!!! Had to use layers of opened newspapers to place over the forms....... it retarded the drying and let the moisture slowly breathe through the paper's pores.

 

 

I rarely use bats, even for most dinner sized plates and small to medium bowls. (Big platters and something like a 24" diameter at the rim bowl... well yes.... bats are for sure used wink.gif .) I just pick them up off the wheelhead. And I throw a lot of smaller things off the hump and pick them off "spinning". If I chose the pieces to be "round" there does not seem to be an issue from the "wet handling". If they are slightly off round, a tiny pat or two at the correct time (not when fresh thrown) takes care of that.

 

And frequently those fresh thrown forms head right out of the studio door and into the graveled kiln yard and into the sun and wind to start to dry for eventual trimming or finishing. When they are trimmed/finished, they also then often go back outside into the wind/sun to dry from leatherhard to bone dry...... before the bisque (although many are stacked in the wood lkiln yakishime... and do not get bisqued). Good clay bodies.

 

A lot of times the issues are claybody issues too....... and not how YOU are handling the pieces. Just because a clay body comes from a "supplier" does not mean it is necessarily a GOOD claybody and the supplier actually has a strong technical background in clay body development. In this country (USA), to be a "ceramic materials supplier company" does not require any certifications or specific training.... just a "shingle" hanging outside the door. I've tried some commercial bodies that are not all that great.

 

 

best,

 

..............john

 

Please post pictures, what does this warping look like?

At the pottery in Japan where I spent some time, distortion through the throwing,drying and firing was appreciated.

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I would agree with a point that John mentioned...drying unevenly. ould your bowls be in a draft and drying quicker on one side?

I lift bowls off the hump and onto boards and put very large rubber made containers over the boards. I have to remove the cover for them to dry but it slows the drying and protects from drafts.

Marcia

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I agree with Niels et. al. As we cycle between winter and summer the heating and cooling air flow changes and habits have to change with it. Anything in a draft suffers. There is a lot to be said for a good sturdy rim too.

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Hi, am new on this forum, but not to throwing pots. I use to have bowls warp every now and then, but after much thinking and much trial and some error, I found that if I flipped the bowl over before it was ready, when it was still soft to the touch, (think Pillsbury Dough Boy), the warping would occur. The reason showed itself after examining all pots during the drying phase. The ones that were flipped over that were soft to the touch warped due to the fact that the bottom of the bowl was heavier than the rest of the bowl, and it would sag just a little, which would throw everything off kilter. I tried out my findings by firing and sure enough, warped pots. So now I wait several days, with the first day the bowl is covered all the way with a plastic grocery bag, and the second day it is dried with only half covered, and the 3rd day no cover. Once the bowl becomes more than soft to the touch, it is flipped over, the sides are strong enough and the bottom is dried enough for the form to stay true. Yes, this adds a few days to your project, but better that than a wasted bowl. I also make sure that my bowls are in the middle of a load, you don't want one side of a bowl to be closer to the elements than the others, because that too will call warping.

 

Hope this helps!

 

 

Mudslayer

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