wayneinkeywest on mon 19 jul 04
Don:
Since the boiling point of water is 100C, it might do well to turn
the temp down on that oven, say to 60C if possible, and try it
again. Too rapid drying (I know, what you're going for is rapid
drying) can cause those faults.
Might be worth experimenting further before deciding it's not worth
it. You might still be able to save quite a bit of time in the
drying process, with no damage to the work. Just my 2¢.
Hmmmm....if I take a blowtorch to my deairing pugmill, with only the
vacuum running....
Would someone please kick me in the head ?
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.45W, Longitude 24.33N
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Don Goodrich"
To:
Sent: Monday, July 19, 2004 6:49 PM
Subject: Vacuum Drying Clay
This is for all you lovers of clay and gadgets, who just can't leave
well
enough alone.
Although the topic is far from current, and originally applied to
plaster molds rather than clay (see the original thread here):
http://lsv.ceramics.org/scripts/wa.exe?
S2=clayart&L=CLAYART&q=&s=vacuum+dry&f=&a=&b=
(the above URL should be a single line)
this may be informative for someone searching the archives some day.
I recently brought home a modest-sized vacuum oven from a defunct
laboratory. It seemed a good idea to experiment and see how
effective it
would be for drying clay. Perhaps it could enable prairie dwellers
like me
to make pots and fire them in the same day like those lucky people
in the
high deserts sometimes can.
I threw a porcelain bowl 6" diameter and 3" high (150 X 75 mm)
with walls about 1/8" (3mm) thick (about twice that thick near the
bottom).
I then turned on the oven part of the vacuum oven, let it heat up to
about
100°C, put the bowl inside and sealed the door. I turned the vacuum
pump on
and drew a 27"(686mm) vacuum.
Results were very quick and obvious.
Within seconds, the bowl had simultaneously bloated, spalled,
flaked, the
bottom cracked and yes, dried.
Some pictures are here:
http://dongoodrichpottery.com/vacdry.htm
Sorry, no movies; but maybe next time.
Obviously not yet a viable production technique, this experiment was
fraught with learning experiences. Foremost, I believe, is that one
does
not do well to rush clay. The advantages of thin and uniform wall
thickness
are also evident, since the thinner parts had the least damage. It
was easy
to watch the progression of drying, from top rim to foot. I could
see how
escaping water vapor bloated the still-plastic clay in the middle
just
before it dried. The final shrinkage at the bottom made a crack
all the way around the outside of the base, and the interior bottom
flaked
as the clay suddenly had to get out of its own way as it shrank and
also
make way for the steam. It was a microcosm of several common defects
concentrated in one high-speed process.
Dunno if this toy has a role in my studio yet, but maybe if the
temperature
and vacuum are less extreme the pot might not be damaged by vacuum
drying.
As they say in the scientific journals, further study is required.
As for
the pot, maybe I'll recycle it, but maybe I'll just fire it as a bad
example...
Cheers,
Don Goodrich in Zion, Illinois
goodrichdn@aol.com
http://dongoodrichpottery.com/
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Don Goodrich on mon 19 jul 04
This is for all you lovers of clay and gadgets, who just can't leave well
enough alone.
Although the topic is far from current, and originally applied to
plaster molds rather than clay (see the original thread here):
http://lsv.ceramics.org/scripts/wa.exe?
S2=3Dclayart&L=3DCLAYART&q=3D&s=3Dvacuum+dry&f=3D&a=3D&b=3D
(the above URL should be a single line)
this may be informative for someone searching the archives some day.
I recently brought home a modest-sized vacuum oven from a defunct
laboratory. It seemed a good idea to experiment and see how effective it
would be for drying clay. Perhaps it could enable prairie dwellers like me
to make pots and fire them in the same day like those lucky people in the
high deserts sometimes can.
I threw a porcelain bowl 6" diameter and 3" high (150 X 75 mm)
with walls about 1/8" (3mm) thick (about twice that thick near the bottom).
I then turned on the oven part of the vacuum oven, let it heat up to about
100=B0C, put the bowl inside and sealed the door. I turned the vacuum pump o=
n
and drew a 27"(686mm) vacuum.
Results were very quick and obvious.
Within seconds, the bowl had simultaneously bloated, spalled, flaked, the
bottom cracked and yes, dried.
Some pictures are here:
http://dongoodrichpottery.com/vacdry.htm
Sorry, no movies; but maybe next time.
Obviously not yet a viable production technique, this experiment was
fraught with learning experiences. Foremost, I believe, is that one does
not do well to rush clay. The advantages of thin and uniform wall thickness
are also evident, since the thinner parts had the least damage. It was easy
to watch the progression of drying, from top rim to foot. I could see how
escaping water vapor bloated the still-plastic clay in the middle just
before it dried. The final shrinkage at the bottom made a crack
all the way around the outside of the base, and the interior bottom flaked
as the clay suddenly had to get out of its own way as it shrank and also
make way for the steam. It was a microcosm of several common defects
concentrated in one high-speed process.
Dunno if this toy has a role in my studio yet, but maybe if the temperature
and vacuum are less extreme the pot might not be damaged by vacuum drying.
As they say in the scientific journals, further study is required. As for
the pot, maybe I'll recycle it, but maybe I'll just fire it as a bad
example...
Cheers,
Don Goodrich in Zion, Illinois
goodrichdn@aol.com
http://dongoodrichpottery.com/
Ivor and Olive Lewis on tue 20 jul 04
Dear Don Goodrich
An excellent experiment.
But I would suggest that if you have a pressure of about 300
kilopascals in your vacuum chamber you might get better results
without catastrophic destruction of your work by reducing rather than
increasing the temperature. My suggestion comes from knowledge that
Vacuum Freeze Drying is used as a way of permanently preserving
delicate biological specimens without destroying their original form
or colour.
At the pressure you used the boiling point of water drops to about 60=BA
C, say 140=BA F. So at 100=BA C you would be creating conditions for the
Flash Generation of Steam. This would mimic the effects of water in a
thick bottomed pot in a normal firing. But you had the added
excitement of you clay being plastic.
I am sure the Shards created by your discovery could be used in an
expressive aesthetic way.
Thanks for reporting this event.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Don Goodrich on tue 20 jul 04
Ivor and Wayne,
Thanks for the encouragement and suggestions. I will indeed do more
tests, using less extreme conditions. After all, the deserts of New Mexico
aren't as hot nor vacuous as my oven, and one can achieve one-day pots
there regularly.
BTW this gadget works really well for drying out small plaster molds.
The porosity must prevent them from blowing up.
Cheers,
Don Goodrich
goodrichdn@aol.com
http://dongoodrichpottery.com/
Jon Pacini on tue 20 jul 04
Greetings All, Hi Don-----
What a fun toy you have. A couple of random thoughts on your
vacuum drying experiments.
Slowing the whole process down is a good idea. As the pressure drops, the
water will boil off on it s own, you shouldn t need to heat it much, if at
all. You ve heard of freeze drying??
Also if your clay is hand made or wedged before using, chances are it has
air in it. It may not have big bubbles, but hand mixed and wedged clay has
lots of little micro bubbles. Even machine de-aired clay may not be
completely de-aired enough for this type of drying. Anyway, the micro
bubbles may be contributing to the bloats/flaking you re seeing. If the
pressure drops too rapidly, the air trapped in the clay will expand, rapidly
forming bubbles/bloats and areas would likely flake off.
If steam was also present in the bloats, explosions could ensue.
What great fun---I can hardly wait for the video----
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
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