[Marcia Selsor]

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

[JBaymore]

trevorpots, on 17 February 2012 - 10:02 PM, said:

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

There is the possibility of embracing that aspect too .

best,

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

[yedrow]

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.

[Mudslayer]

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

[neilestrick]

yedrow, on 18 February 2012 - 05:38 PM, said:

There is a lot to be said for a good sturdy rim too.

Definitely. If the rim is thickened, it not only helps prevent warping but frames the pot nicely, too. Flaring the rim will also help to stiffen it.

[Nelly]

trevorpots, on 17 February 2012 - 10:02 PM, said:

JBaymore, on 17 February 2012 - 01:34 PM, said:

neilestrick, on 14 February 2012 - 10:33 AM, said:

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 .) 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.

Dear All,

Another thought on this is to put a piece of newspaper on top of the lip of the bowl when transferring either the bat or actual bowl directly from the wheel head. This traps air. Air holds the shape of the bowl. After a half and hour or two of the newspaper sitting on thevessel on the table I gently remove the newspaper. The lip is usually contained and the bowl or vessel lip does not distort or warp. The air has been trapped a reasonable amount of time for the bowl to set-up somewhat.

But I do agree, slow drying is crucial. I have lost lots of pieces due to trying to speed up the drying process. Warping can happen. It is disappointing.

Right now with some large platters I am noticing that the in my haste to dry, they are curving up at the edges (i.e., not sitting as flat as I would like). Sometimes I use some light weight to flatten them during the drying process and alternate these heavy objects every day or so. But it is tricky. Sometimes it works and sometimes it doesn't.

The controlled drying cabinet is another great suggestion. It is not hard to construct either. As said, a simple piece of plastic over a contained shelf can work well.

Lastly, I find that it is also important that drying, if done with simple plastic around the bat be, at first, fully surrounding the vessel. Don't just tuck it around the bat. Try to enclose it carefully. As increased drying occurs you can slowly release the plastic and simply tuck it around the bat. For me the entire enclosure works well for at least the first day or two.

Nelly