Warped pedestal base

[Hal Tenny]

Does anyone know what can cause the bottom of a pedestal base to warp like in the image? This piece was sitting flat on the shelf, well away from the edge. I've done many pieces with pedestal bases and never had this problem, then all of the sudden, 2 in the same load did it. It was a fast glaze fire at cone 6. Highwater Bella's blend clay I think. Do you think a re-fire will fix it?

Thank you~

[Pres]

I have done many pieces with pedestal bases over the years also. From my perspective (IMHO) it looks like the flare of you base is to extreme for the thinness of the base. I am always wary of base that flare to the extreme.  The amount of stress would not show up in bisque fire, but a glaze fire is a different story. Years ago I demonstrated to some students how soft the clay was when I put a steel rod into a peep hole to push the side of a pot in. After the firing had cooled the students were awed at the indent of 3 inches in the side of the pot.

 

best,

Pres

[Hal Tenny]

Ah... they are a bit on the thin side, Pres.  This pedestal is closed on top for the upper structure, so I actually threw it upside down for a nice finished base inside. So by inverting it, it put the thinner lip on the bottom. I also noticed on this piece and the other I had trouble with are both naturally off balance because of the design. The center mass of the piece is off center, and both of them leaned toward where the most weight was located. So it's probably a combination of both of those things. Thanks for looking~

[neilestrick]

I always fire open-bottom pieces like that on a waster slab. Helps a lot. Refiring may flatten it out. Try it, on a slab, nothing to lose at this point.