Handbuilt porcelain mugs

[Dragonfly Pottery]

Since the covid pandemic, I have been handbuilding with porcelain at home, where I have no wheel.  I find I love it!  But...I have recurring issues with my mugs (and espresso cups) warping out of round.  I am careful to create well-shaped vessels, but they, more often than not, warp out of round as they dry.  I tend to build with rather thin slabs (1/8"-3/16") because I love a thin, lightweight cup.

Any ideas for how to keep them round??

[Min]

How are you rolling out the slabs and forming the mugs and cups? How heavy a handle is going on them? Are they warping oval towards the handle? How are you drying them? Are using witness cones to check for over firing?

Could you post a picture or two of them? 

[Dragonfly Pottery]

I am hand rolling them on a flat, muslin-covered surface, with thickness-controlling bands on my rolling pin.  

I'm putting a thinnish handle on them, and cutting the handle about 1"-1-1/2" from the top joining point, then overlapping the handle parts, thinking that the density of the handle may be pulling the cup out of round.  I'm hoping that cutting and overlapping the handle will reduce the pull on the cup. 

I'll enclose a few pictures.  

The all-white one is a freshly made, still green-but-dry mug, the cobalt espresso cups are fired, with Dk. blue celadon glaze on the outside, and a plain white glaze on the inside.  I am in the process of trying a cobalt aluminate mason stain-colored porcelain slip covered with a plain Wollastonite clear glaze over all to help reduce the warping on the espresso cups. The jury is still out on the slip-colored vs. glaze colored rate of warping--but I'm trying different approaches!

 

[Min]

@Dragonfly Pottery, thanks for posting the pictures, always helpful. I think because of the fairly straight up and down wall of the espresso cups they have less of a chance of warping than the mug in the 2nd image. Also, if you can avoid that thickening of the handle to reduce the mass that should help. I'ld try a couple mugs with a lower handle placement also, having the weight close to the top is going to exacerbate the handle pulling the rim out of round. Thicker slabs would help too. Are you re-rounding the rims after attaching the handles? A bisqued former, (tapered like the top of an acorn) or a plastic cup helps to re round rims if necessary.

[Callie Beller Diesel]

The warping in your images, especially the two on the left, looks like the kind you get when you put a supporting hand on the inside of a slightly too flexible mug when you apply the handle. 
You might try using a plastic cup on the inside of the mug you’re making to hold it in round while you’re working, or letting things set up a bit more before attaching. 

[Chilly]

I use a thin plastic bag, and the some kind of funnel-shaped, light-weight item inside the top to keep hand built mugs round.  Clay has memory, and if the mug was born as a flat slab, it wants to get back to flat.  The wetter it is as you form it, the less chance of it wanting to ga back to flat, but the more chance of it slumping !  Probably why the potters wheel was invented.

This video, very briefly, shows the funnels put into mugs at the Emma Bridgewater pottery in Stoke-on-Trent.  Watch at about 16 seconds.