John Baymore on mon 25 sep 00
......... with Don Rietz and he did the most OUTRAGEOUS thing - he had us
fire WET pieces... Out of this massive gas kiln (packed tightly, includi=
ng
pieces IN THE FLUE), came beautiful unbroken salt-fired pieces.
Not so outrageous..... just very a smart, well educated ceramist.........=
and a good well honed "showman" . (Not knocking the showman part.....=
...
that is part of the "sizzle" of workshops . Reitz is one of the best
presentors that I have ever seen......and I love his pots.)
This "trick" (which it really isn't) takes advantage of the fact that if
the partial pressure of water in the kiln atmosphere is very high, you ca=
n
control the ware drying quite effectively. At any given temperature and
pressure, air (or any mixture of gases) can only hold a certain maximum
amount of water vapor. (This is why "dew" happens as the night air chills=
..)
Water migration problems (blowing up in potter parlance) tend to occ=
ur
when the outer surface of the piece drys first....closing the microscopic=
pores the water needs to travel through to evaporate into the air. Then
the water inside can't get through.....and can take a section of wall wit=
h
it . If the pots are really evenly wet....this doesn't tend to happen=
.. =
So you pack the kiln with wet pots, fill the kiln with water saturated
gases by warming the wet pots to start evaporating the water, and then
slowly lower the humidity in the chamber by deft control of kiln
circulation ....... thereby allowing the pots to dry evenly throughout. =
Can be done in an electric kiln too....but much easier in a fuel fired un=
it
due to the contribution of some H2O vapor from the byproducts of combusti=
on
and the generally better circulatory qualities of most gas kilns when
compared to the typical studio electric. =
This is the concept behind many industrial drying units. In this case the=
kiln was acting as the "dryer" as well as the kiln.
With a good commercial dryer unit you can dry wet pots incredibly fast an=
d
evenly without cracking. Industry has this down to a science ........
which it IS. =
The reason pots can SOMETIMES be placed in the flue areas of SOME kilns
(Reitz has "been around" and KNOWS on sight when this can be done) is tha=
t
for the most part studio potter's site built gas kilns typically have exi=
t
flues that are WAY oversized. Comes from references in most pottery-type=
kiln building books. So some restriction to the flow in that part can
easily be tolerated.....in fact can often improve firing performance.
What I learned was that I have a lot to learn about gas-fired kilns and
that it takes incredible patience, a good sense of smell and the ability =
to detect subtle heat-changes to do a good firing. =
Good observation. Ceramists need to devote the same level of attention t=
o
each and every aspect of ceramics that they do to forming. Forming issue=
s
seem to get all the attention....often to the detriment of stuff like
surface enrichment, glazing, and firing . Much to be learned in orde=
r
to really handle glazes and really handle kilns. That is why this art fo=
rm
is so technically demanding . It ALL has to work together well to get=
the final end result.
All your senses can, and should, be utilized to gain information when
firing. Good instrumentation (guages, flowmeters, pyrometers, flue
analyzers, calibration on dampers, etc.) is an aid to developing this
ability to use such intuitive understanding.
Best,
.......................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 18-27,
2000"
NLudd@AOL.COM on mon 25 sep 00
John Baymore (JBaymore@COMPUSERVE.COM) writes:
>All your senses can, and should, be utilized to gain information when
>firing. Good instrumentation (guages, flowmeters, pyrometers, flue
>analyzers, calibration on dampers, etc.) is an aid to developing this
>ability to use such intuitive understanding.
Hi John
Thanks for the wet-pots-in-kiln explanation and the above great advice - I'll
go along with that.
I see that of the four devices you mention, two I have never heard of:
flowmeters and flue analyzers. I suspect I'm not the only one in the dark
here - would you please tell us what they are?
thanks for any enlightenment!
Ned (a mud & water man by nature, now bisquefiring the Beast for only my
second time - an ageing 18 cu ft gas kiln with four burners and a mighty
pressure behind them. Really, I mean really, wanting to understand more
what's going on inside - as the next firing will be a cone 10 with a lot
riding on it!)
Steve Mills on tue 26 sep 00
We do a lot of firing for the kilnless and one trick we use with thick
or heavy ware in our 4 cube Electric Kiln is to set the controller to
soak @ 110oC, and the heat input @ 10 percent, close the whole thing up
tight and let 'er sweat overnight. Works every time; dry ware and no
bangs!
Steve
Bath
UK
--
Steve Mills
Bath
UK
Martin Howard on wed 27 sep 00
Steve, I'm very interested in this method you describe.
I was taught to leave all holes open when bisque firing.
So, now that I raw fire for most of the ware, I leave the kiln top open
while the temperature is going up, ramping very slowly. So overnight it may
only have reached 200 C. Next day I let it rip upwards and then soak at top,
1100 - 1140 for one hour. Close up, so that everything cools slowly.
It costs me more in electricity, than when ramping high.
Are you suggesting, close up from the start; ramp slow; then soak at top
temp?
Trying to follow the method. It may save me a few pounds in electricity
costs.
So many things we are taught seem to crumble when we find someone who has
accidentally or experimentally done it another way.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
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