search  current discussion  categories  techniques - cracking 

shrinking/cracking

updated sat 31 may 97

 

Boyd on wed 7 may 97

Question: Does clay have a greater propensity for cracking on the bottom
during drying when using a non-absorbent bat as opposed to one that will
absorb? I'm talking about large,heavy pots, base, 15" + using stoneware
with shrinkage of aprox. 12%. Pots average 40 to 60 lbs.

Boyd
Iron River MI

The Shelfords on thu 8 may 97

Hi Boyd -

Re:
>Question: Does clay have a greater propensity for cracking on the bottom
>during drying when using a non-absorbent bat as opposed to one that will
>absorb? I'm talking about large,heavy pots, base, 15" + using stoneware
>with shrinkage of aprox. 12%. Pots average 40 to 60 lbs.

For what it's worth (my experience is with stuff of not more than15 lbs or
so - clay and shrinkage sound similar) - I had more problems with cracking
on plastic bats when I first started using them, than with wood. I dealt
with it by cutting through at the base of the piece several times during the
early drying process, and, if the piece was very large (by my standards -
yours are another world!) covering the top 2/3 with plastic and letting the
part near the bat be open to the air. I usually try to get it off the bat
as early as possible in the drying process. No problems after the first few
disasters.

- Veronica
____________________________________________________________________________
Veronica Shelford
e-mail: shelford@island.net
s-mail: P.O. Box 6-15
Thetis Island, BC V0R 2Y0
Tel: (250) 246-1509
____________________________________________________________________________

Doug Gray on thu 8 may 97

Boyd,

I beleive it is safe to say that drying is best if it is done evenly and
slowly. The probablem with non-absorbant bats is that the pot/vessel
dries very slowly, if at all, on the surface that it touches the
non-absorbant bat. Unless the drying is watched carefully, you could
have areas that are very wet and other areas that are almost dry. This
will/could cause some problems for you. I have used both, and am not
suggesting one is better than the other.

Doug Gray
Alpine, TX

Tony Hansen on thu 8 may 97

> Question: Does clay have a greater propensity for cracking on the bottom
> during drying when using a non-absorbent bat as opposed to one that will
> absorb? I'm talking about large,heavy pots, base, 15" + using stoneware
> with shrinkage of aprox. 12%. Pots average 40 to 60 lbs.

Pots crack when they dry unevenly.
A non-absorbant bat encourages pots to dry unevenly, an absorbant one
sucks water out of the bottom and speeds up the drying of normally the
slowest drying part.

--
=================================================================
Tony Hansen, IMC thansen@mlc.awinc.com
INSIGHT5/Magic of Fire II demos at www.ceramicsoftware.com

Bill Buckner on fri 9 may 97

I use ware boards I have scrounged from various soueces. Some are
varnished and therefore, non-absorbant. I simply cover the board with a
sheet of newspaper. The wicking action of the paper allows the bottoms to
dry at a rate fairly consistant with the rest of the pot.

-Bill

Bill Buckner e-mail: bbuckner@gsu.edu
Georgia State University http://www.gsu.edu/~couwbb

On Thu, 8 May 1997, Doug Gray wrote:

> ----------------------------Original message----------------------------
> Boyd,
>
> I beleive it is safe to say that drying is best if it is done evenly and
> slowly. The probablem with non-absorbant bats is that the pot/vessel
> dries very slowly, if at all, on the surface that it touches the
> non-absorbant bat. Unless the drying is watched carefully, you could
> have areas that are very wet and other areas that are almost dry. This
> will/could cause some problems for you. I have used both, and am not
> suggesting one is better than the other.
>
> Doug Gray
> Alpine, TX
>