[Clayart] Throughing thinner?

ran mcc ranmcc at msn.com
Thu Oct 27 20:18:39 EDT 2016


Robert I would like a pic of your bowl.
ranmcc at msn.com


Sent from my Verizon Wireless 4G LTE smartphone


-------- Original message --------
From: Robert Harris
Date:10/27/2016 4:10 PM (GMT-05:00)
To: Clayart international pottery discussion forum
Subject: Re: [Clayart] Throughing thinner?

I throw thin and occasionally I get warping especially on bowls the size of
the ones Randy is talking about.

If you're having problems with deformation while the pot is plastic I would
suggest a) throwing with less water (easier said than done!) and 2) zapping
it with a blow torch/heatgun before you take it off the wheel.
3) Don't trim the base by resting such a large bowl on its rim. I throw a
large chuck which the centre and strongest part of the bowl rests on.
It is also important to dry these things as evenly as possible. (Slow is
not necessarily better, just evenly). The easiest way to do this is put it
in some sort of box with holes in it.

None of this really helps with true warpage (as opposed to plastic
deformation) in the glaze kiln. For that there is really only one
suggestion and one "real" solution. The first suggestion is to make sure
your kiln shelves are dead flat - and if possible as even as possible. For
a large bowl I put it on an extra kiln shelf that I know is flat, and level
it with fibre or wadding (I don't go overboard on getting it level but I do
spend a couple of extra minutes).

But the real solution is ENGINEERING! Design a bowl that can be large and
thin and won't warp.

Everyone has a different "look" to their bowl so it's a bit difficult for
me to advise what to do, but the most obvious thing to do is to thicken up
your rim. Just like Susie's newspaper trick, a thicker rim will go a fair
way to preventing warpage. You can then run into the problem that Vince
mentioned where the pot looks lighter than it "should", however. Personally
I throw a large flange type lip on my large bowls that is about 25 degrees
above the horizontal. It actually has a slight curve in it that strengthens
it, and this flange has a very thick rim on it, which is less noticeable as
it's edge on to the viewer (the flange itself can be reasonable thin).

Also consider increasing the diameter of your foot a little. Finally make
sure the wall of the bowl has a true taper. With the exception of the rim
(which we've discussed and which should be well compressed!), the walls
must be as evenly tapered to the top as possible (including the flange, if
you have one). I once threw a bowl (about 20", wet) where the bottom 1/3
was either the same thickness or marginally thinner than the top 1/3 and
the whole thing just sat down around the foot! Basically if you get
everything as even as possible (and of course this includes as little
wobble as possible in the thrown form!) then you'll minimize the chance of
warpage.

Finally ... try to embrace a little bit of warpage! It's a handmade pot
after all! I have recently mentioned the diamond lap disc I have for
smoothing off feet. With a bit of work it can flatten the foot of a warped
bowl, so that at least there's no rocking.

Hope that helps,

Robert

P.S. I'm happy to send pictures directly of the type of large wide bowls I
make if anyone is interested.


On Thu, Oct 27, 2016 at 8:04 AM, Susie Hite <hiteshome at bellsouth.net> wrote:

> I don't usually comment, but I understand the desire to throw thinner.  I
> love a lot of the Japanese pottery and it is usually thin.  I have
> unfortunately found that when I throw thin it almost always warps.I feel
> your pain. The few times I've been successful was when I was able to put a
> piece of news paper over the rim as soon as it was firm enough not deform
> the bowl, then when it was leather hard finish drying upside down.  Also
> bisque fire upside down.  There's no guarantee it won't warp in the glaze
> firing. =0(After all that it's still as Vince said very fragile.It's still
> fun to try every once in a while.
> Good Luck!!!Susie
>
>     On Wednesday, October 26, 2016 9:58 PM, ran mcc <ranmcc at msn.com>
> wrote:
>
>
>  Guess it was just a thought. Been making pottery for 40 years.  No
> training.  No mentors.  Pretty isolated from the clay community except for
> clay art.
>
>
>
> Sent from my Verizon Wireless 4G LTE smartphone
>
>
> -------- Original message --------
> From: Vince Pitelka
> Date:10/26/2016 9:06 PM (GMT-05:00)
> To: 'Clayart international pottery discussion forum'
> Subject: Re: [Clayart] Throughing thinner?
>
> Hi Randy -
> I am curious as to why you would want to lighten them up more.  "Too
> light" is a real problem in functional ceramics.  Unless this is a
> conceptual project to produce non-functional "bowls," the weight in your
> bowls serves an important purpose.
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft
> Tennessee Tech University
> vpitelka at dtccom.net
> https://sites.tntech.edu/wpitelka/
>
>
>
>
> -----Original Message-----
> From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf
> Of ran mcc
> Sent: Wednesday, October 26, 2016 11:19 AM
> To: ClayArt <clayart at lists.clayartworld.com>
> Subject: [Clayart] Throughing thinner?
>
> I like to throw 12lb bowls that usually will reach to 18 to 19 inches.
> Using Red Stone from Carolina Clay.  12lb bowls will fire out to about 7lbs
> with glaze.  I would like to get these bowls lighter in final weight.  I
> know I can make sure the bottom is minimum thickness,  I know I can trim as
> much as possible.  I just don't want to get warped bowls.  Are there some
> techniques you can share to get pieces as thin and light as possible
> without causing warping in the fire?  Suggestions on maybe a better clay
> that will hold up better to thin throwing without warping?  Any other
> suggestions?  Thanks for any help.
>
>
> Randy
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