Lorri on sat 15 jul 00
OK, thanks for the answers to my throwing stick question and my anagama
question.
I have one more. There was a recent question about pots blowing up in the
kiln. While I don't have that problem, I have had some pots cracking on the
bottom. Here's my situation. I have been using a cone 5/6 buff clay thrown
on the wheel. When I throw, typically not on a bat, just on the wheel and
remove the pot onto newspaper. I have been experimenting with making lidded
jars. I place the lids on the jars once both are trimmed so that they'll
dry together. Because of this, I don't turn the pot upside down when
drying. When I bisque fire (to cone 04), it is very slow. I preheat the
kiln overnight with kiln lid open at the highest notch with peeps open;
lower the lid to lower notch but not all the way down and leave on low still
with peeps open for 3-4 hours; close lid all the way and turn to medium and
put peeps in for 3-4 hours; then turn on high to complete firing. My
thoughts are that maybe I should be turning the pot upside down for more
even drying. If so, will the lid still conform to the pot? OR maybe I
should cover the pots with plastic and dry slower. I don't think I am
trimming too thin - don't think this is the problem. It appears to be more
often on the lidded jars than on the items without lids, but not
necessarily. Maybe a third of the bisque-fire items crack. Half of those
are all the way through, and about half are only cracked on the outside.
Any thoughts on why the bottoms of the pots are cracking?
Love the wealth of information and the willingness to share on the list.
Lorri
Lenexa, KS
Cindy Strnad on sat 15 jul 00
Lorri,
Do your lidded jars tend to have wider flat areas at the base than other
items? Large flat areas do tend to crack a lot more than smaller bases. I
dry my lidded pieces with the lids in place. Sometimes I dry them on
sheetrock/drywall, but usually just on the particle board shelves I dry most
everything on. My studio is in the basement and usually very damp, so it
takes them a long time to dry. Some other things I will set outside after a
day or two to let them dry faster, but I never set the lidded jars (even the
small ones), platters, or any other items with large bases out in the sun
unless they already appear to be bone dry. I have done it, and the bases and
lids both crack.
So, I would say first to try draping plastic over your lidded jars as soon
as this can be done without marring their surfaces. Second, dry them on an
absorbent surface such as plaster or sheetrock (or change the newspaper
often). Sheetrock scraps can be had free at most any construction site. Lots
of the stuff gets thrown away--just like when you're making a dress--you
always have scraps left over that you don't have much use for unless you're
a quilter. If you don't want to scrounge, sheetrock is still pretty
inexpensive at the lumber yard.
Second, if that doesn't work, try buying a groggier clay, or adding grog to
your clay.
Third: When you knead the clay, instead of rounding out your pug in the way
the clay is already shaped, turn it on its *side*, then re-shape it into a
throwing pug that way. For some reason, this does seem to work well for me.
Or maybe its a combination of that and the slow drying.
BTW, there's lots on this subject in the archives--you might want to do a
search.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
earthenv@gwtc.net
WHew536674@CS.COM on sat 15 jul 00
Lorri,
What I have found helpful in drying bottoms that I don't want to turn up side
down, is to put them on an oven rack. I usually dry slowly. Put the lid on,
put the pot on the oven rack so air can get to the bottom, cover with plastic
for a couple days, and never had any problems with cracked bottoms.
Joyce A
Mission, TX
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