It is likely that your heads were not dry enough or were fired too quickly,
or the kiln may have been too full.
I have fired large clay sculpted busts of varying thicknesses for 11 years
and have had almost 100% success. Letting them dry for a couple of weeks
(make sure that they are propped up so that the inside dries also), then
firing them overnight at the lowest settings with the kiln door cracked
open, and then bringing up the temperature slowly over another 12 hours has
Once I glazed fired a bust which had already been bisqued fired in a samller
kiln. Though I fired it slowly, it still cracked; so I assumed a large
piece needs a certain amount of space around it.
Hope these suggestions help.
At 10:29 PM 6/2/97 -0500, you wrote:
> My Introduction to Art students made clay sculptures this
>spring. Our school has another art teacher who has the kilns in her
>room. She fired the clay for us.
> ALL the clay heads in the Alpine kiln blew up! The majority of
>the heads in the electric kiln were fine. The color of the heads in the
>Alpine kiln was sort of gold, even brownish; the color of the fired clay
>heads in the electric kiln was basically white.
> A few weeks before the other teacher fired the example clay head
>I made; it came out perfectly. I used the same clay on the head I
>made; the walls of the clay head were about the same as those of most of
>the students. Three years ago my students did this project; most of the
>heads were fired successfully; I also had a similar experience several
>years earlier--they came out ok.
> Would you assume that the clay was fired to too hot a
>temperature in the Alpine? That the clay was fired too quickly--not
>candled...? I know it could not have entirely been because of the
>thickness of the walls of the clay, or mine would have blown up, too. I
>would like to avoid this problem in the future.
> The other teacher says that the problem was because they were
>all too thick; some of them probably were too thick.
> Any help would be appreciated.