Warped Pie Plate Bottom

[giltex]

I just fired a 9" pie plate and got a warp in the bottom. Laguna Speckled Buff, slow dry with scalloped rim covered, slid from bat to drying board after several days, bisque 04 slow, light clear glaze on bottom three wire stilts to suspend from the shelf. The bottom in the middle is about 1/4 thick. I did not pull out to form the sides, but continued to press from the middle -out then raised the sides. Any ideas why I got the warp. Oh BTW fired to cone 5 fast. Normal cooling. Glaze is beautiful.

[Chris Campbell]

I am suspecting it has to do with the cone 5 fast, normal cooling and the difference in the thickness of your bottom vs the sides.

You took all that care through to the bisque firing then hurried the next, hottest part.

I think part of your plate cooled quickly and part retained the heat and buckled.

 

Unless you are in a huge rush for something, fire at medium speed then do a controlled cooling.

Electric kilns generally cool too fast and this can stress pieces you want to cool down evenly.

Many kiln manuals have examples of how to do controlled cooling.

[giltex]

Thanks for the input Chris. You are probably right. I have a tendency to rush Christmas!! I have the MC6 schedule in the kiln, will tweek it a little and try that. I will have to be careful about the glazes I use cause some of them don't like the MC6 firing schedule.

[kilndoc]

I have to agree with Chris on this. More than likely, it had to do with the speed of the firing. Take the time to slow down, the pots will be better for it.

 

You certainly aren't alone, either. There is a great contingent of potters from all levels of experience and academia that tend to rush the glaze firing. Often this comes from a time-management issue (I know I always seem to be just 'behind' schedule ), but for some its intentional.

 

For those people, the general thought seems to be that the clay is 'done' or at least 'unseen', so if the glaze looks right, then the pot is right. I couldn't disagree more. There are just too many things actually happening during a firing, and rushing it typically (for me) leads to a piece that might be *nice*, but would have been better if it weren't for....(insert description of defect here). Now that certainly doesn't mean that Fast speed is ALWAYS inappropriate, just that it is not usually the right choice for normal glaze firings.

 

As a former professor of mine said to me once "Its taken the clay millions of years to get to THIS point, why do we think we can speed up the LAST step?"