Warping mugs

[D-Walk]

Hey all,

 

I've always had a bit of an issue with wheel thrown mugs I create warping a little bit out of round during the bisque and glaze firings. Not all my mugs will do this, or even half, but it seems I've always got several mugs in each firing that end up a bit 'out of round'. I don't make the walls of my mugs especially thin (which I thought could be one cause), and I check them during the drying process to make sure they're keeping their shape. All I can figure is some sort of surface tension created by the handle that's pulling it out of round during firing. Thoughts, comments, sarcastic remarks??

 

D- Walk

[bciskepottery]

Could you be distorting the shape removing the mug from the wheel or bat after throwing? I have styrofoam cups -- coffee size -- that I've removed the bottom from and then place inside the mug to help keep roundness while drying. The styrofoam is pliable and gives while the clay is dryng (bad experience with plastic solo cups that are more rigid). Removing the base of the styrofoam cup makes them flexible. You can even use the styrofoam cup to restore roundness by twisting it inside the mug. Keep the styrofoam cup somewhat loose -- don't jam it in or push it in tight agains the rim. Just enough to keep the shape.

 

If you put the top of your handle directly on the rim, you could be creating some distortion; try lowering the top of the handle and see if the problem persists.

[D-Walk]

Thanks for the reply. The handles I put on are below the top of the rim, probably 3/4" down from there. The warping seems to happen during the firing; the shapes look good during the drying process. It's when they come out of the kiln I notice it.

[Mark C.]

I would like some more info before commenting

What cone are these fired to -electric-reduction-is the clay body made for that range

Porcelain or stoneware?

Are the handles large (4 finger or small one finger)

A photo would be great but if not could you give some more info?

Are you handling when the mugs still distort or are they going out of round after the bisque fire?

Mark

[TJR]

D-walk;

I had the same problem for a while. In one of Simon Leach's videos on youtube he shows how to push mugs back on round after putting handles on by gently taking a fired round bottom pot and re-shaping all of his mugs. It's a little thing. I tried it, and it really works. I fire stoneware and porcelain at cone9-10.

TJR.

[OffCenter]

D-Walk, warping during the glaze firing is not an uncommon problem and can have several causes, but warping during the bisque is. Stress caused by putting on the handle, clay memory and all that should show up during the drying. If stress problems show up in the bisque it is usually in the form of cracks, not warping. Are you sure they aren't warping during drying? What clay? What cone do you bisque to? Pics?

 

Jim

[macdoodle]

worked hard on thinking up a sarcastic remark, but darn.... anyway, I'm not a thrower -but- I wonder if a few are very out of round when thrown and though you straighten - they remember...are you rounding up while still super wet so they maybe don't have the memory built in- or later in the drying ?

 

I made some hand-built containers and one I shaped up while wet is pretty round one rounded up when a little drier is more out of round. Could just be coincidence but .....may be worth your while to test that theory.