Tadeusz Westawic on wed 29 oct 97
Okay, I read most of the posts on firing wet pots.
In seasons other than winter, drying time (wheel to bisque fire) is two,
two-and-a-half days, max. My studio is heated in winter only when I'm in
it. In wintertime things dry slowly and too wet pots run the risk of
freeze-cracking, so I had been bringing them into the house to dry.
A few of the posts on firing wet pots mentioned kiln drying. I was in a
tight spot for bisqueware for an upcoming demo and decided to try it. I
loaded five cylinder forms into my Duncan electric which has a preheat
setting. I loaded them bottom-down (right-side-up). Three of the five
had two days shelf drying and were visibly dry half-way down from the
top and darker (visibly damp) through the bottom half. The other two
pots were only one-day shelf dry and were visibly damp bottom to top.
The kiln lid was left wide open.
Things were looking pretty good for about the first three hours. All of
the pots looked bone dry but a touch revealed that moisture was still
evaporating. I happened to glance down inside the pots when I saw the
cracks.
The two dampest pots, the one-day shelf-dry in damp weather, had
developed bottom cracks, one in a shallow, off-center arch line, and the
other in a centered three-point star. The other three pots (the two-day
shelf dry) were okay.
Well, obviously there is some stressing going on here. I have no doubt
that the three "okay" pots are also bottom-stressed but not to the point
of separating. I'm not too concerned because the final fire will be
essentially earthenware temp (raku) and I'll probably leave them at the
demo site anyway, cracks or no cracks. However if I were to take them to
vitrification temperatures, I suspect that bottom cracks would reveal
themselves.
So, my friends, this is one potter who will be carrying his damp
greenware to the house for shelf drying again this year. Well, maybe
I'll try setting some upside-down and try again anyway.
Tadzu -- In sunny but chilly SW New Mexico at 6000 ft.
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