Matthew Bullis on mon 18 jan 99
I understand that if you don't watch your piece, it will break open inside
the kiln and that will be because of air bubbles. How do you prevent this
from happening?
Thanks a lot.
Matthew
Net-Tamer V 1.11 - Test Drive
Theodore Banton on tue 19 jan 99
Air bubbles have never exploded on me in a bisque firing- it is not air tight.
The problem is that some people fire without drying their pieces extensively,
thus when firing, the air is trapped by the water left in the clay resutling
in a grenade in the kiln.
Ted St Augustine
Kathleen Weiler on tue 19 jan 99
Wedge, Wedge, Wedge!! before throwing.
kw
Gayle Bair on tue 19 jan 99
Mathew,
If your clay is properly wedged not only do you align the
clay molecules but you get out any air bubbles. So wedge
your clay well. If you can feel the bubble on your sculpture
take a needle tool and pierce the bubble several times then
smooth it to compress the clay which forces out the air.
Gayle
Lili Krakowski on tue 19 jan 99
There are two kinds of air bubble problems. The first is that the clay is
badly wedged--i.e. kneaded--so air bubbles are left in it. The other is
that when pieces of clay are added on they are not shoved in tightly
enough so that air gets trapped. Now neither is an oh-my-goodness crisis
problem IF YOU CHOOSE YOUR CLAY RIGHT. You say you are a novice, yes?
well I hope you are not new to food. Imagine a bowl of mashed potatoes
(mashed turnips if you are on a diet! Gee some people!) Now you know from
sticking a spoon or finger in how dense the stuff is and it makes these
plop plop bubbles when it boils. BUT if you were to add croutons then
there would be something like spaces between the strata of mush. Right?
Well most clays are like the mashed potatoes. So when there is air
trapped in there, and it wants to come out in the fire, and there is steam
in there which is the result of the water that is part of the clay
molecule turning to steam and needing to come out, you get tremendous
steam pressure and boom! There also is some organic matter and some other
stuff that turns to gas, same idea, boom! But we add something called
GROG--which either is finely crushed firebrick, or ground up bisque. This
stuff has already been fired and it acts as the croutons do (except
croutons will turn mushy themselves after a while, and grog does not.) the
bits of grog act like tiny spacers that allow the steam and gases to sneak
aroudn them and OUT
so what you really want to do is get some clay that is made for sculpture
and has grog in it. Then allow your pieces to dry very very slowly. Why
is that? Ok. Because pieces dry from the outside first. As they dry
they shrink. So if the outside dries before the inside does, you guesssed
it--the outside has become so closed and impervious through shrinking the
water inside can't get out. Dry slowly-I woudl suggest in a styrofoam
cooler, or equivalent, and even then cover the piece in plastic--loosely.
Lili Krakowski
Rick hugel on tue 19 jan 99
Two possibilities exist. One is that you are not properly wedging the clay
or you are wedging too much at one time and are not able to do it smoothly.
The other is if you are hand building with coils, you are not properly
sealing out the air as you built up the piece.
>----------------------------Original message----------------------------
>
>I understand that if you don't watch your piece, it will break open inside
>the kiln and that will be because of air bubbles. How do you prevent this
>from happening?
>Thanks a lot.
>Matthew
>Net-Tamer V 1.11 - Test Drive
Donn Buchfinck on wed 20 jan 99
air bubble do not cause pottery to explode
nore to fall apart
it is water that is left in the clay that cannot escape fast enough when you
pass the steam out stage around 220 degrees F
even if you think your pot is dry, if you have a paper thin wedge of water the
pot will go boom
the best way I have found to wedge is to use a wire and cut the clay and bring
it back together 20 times
put the clay back together with the cut ends going away from you
this gives about a million layers and drives all the air out of the clay
it stacks the clay particles up like sheets of paper
then after I am done wedging I spiral the individual clay balls to get them in
shape for throwing.
good luck
Donn Buchfinck
Bruce Girrell on sat 23 jan 99
I was going to post a similar question months ago, but went to the archives
and saw that there were plenty of wedging threads already there, so I read
some and went back to the wedging table. Maybe the advice helped, maybe it's
just practice, but I'm getting better.
I would like to add this, though. Most texts that I have read mention
wedging as something that you need to do. A few attempt to describe the
process, but devote little more that a few sentences to it. Maybe I missed a
tape here or there, but I haven't seen the wedging process in any of Robin
Hopper's tapes and Stephen Jepson covers it for about fifteen seconds in
his - no close-ups or slo-mo.
Such a fundamental operation, and it seems as though we're simply supposed
to know how it works.
I attempted to follow the directions in the books and I watched the Jepson
segment time after time. No matter what I did, I seemed to do something in
the wedging process that would cause a flap of clay to fold over the main
lump that I was working. To me, that means that I just trapped some more air
into the lump.
I have developed a rhythm of my own now that seems to work as evidenced by
encountering fewer bubbles during throwing, but I would ask anyone who is
considering doing a book or video to please spend some time on this subject.
Many of us, particularly the beginners, do not process sufficient volume or
have sufficient money to warrant the purchase of a pug mill.
Bruce "my rant for the day" Girrell
| |
|
