Gail Dapogny on tue 23 apr 02
A thought-provoking hypothetical question came up at our guild today.
Suppose you are tending the kiln and it is close to the end of a full day,
13 hour, cone 10 gas reduction firing and you're soaking: temperature is
holding at about 2290 f; you lose consciousness or die or something, and
nobody discovers the kiln (still firing/soaking) for another 12 hours.
....What would happen during that 12-hour period: meltdown of the pots,
certainly. But what about the hard brick of the kiln interior; exterior;
for that matter what about the whole building? One person said that nothing
would happen because the temperature is no longer rising. But several of
us felt that the residual heat could be a major problem.
Just curious. Anyone have an informed idea? (Or uninformed, for that
matter.)
---Gail
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
http://www.silverhawk.com/ex99/dapogny (single historical photo - no longer
registered with Silverhawk)
Arnold Howard on tue 23 apr 02
Gail's question about overfiring pertains to gas kilns. I don't
know the answer about gas kilns, but do about electrics.
Some kilns won't over-fire. For instance, the Paragon X-14J for
china painting. It just doesn't have enough power.
Other kilns, of course, could easily over-fire if the power were
locked on. If that happens, the ware will collapse, the bricks will
glaze over, and the elements will eventually burn themselves out.
But the heat will remain contained within the kiln.
Arnold Howard
Paragon Ind. Inc.
--- Gail Dapogny wrote:
> A thought-provoking hypothetical question came up at our guild
> today.
> Suppose you are tending the kiln and it is close to the end of a
> full day,
> 13 hour, cone 10 gas reduction firing and you're soaking:
> temperature is
> holding at about 2290 f; you lose consciousness or die or
> something, and
> nobody discovers the kiln (still firing/soaking) for another 12
> hours.
> ....What would happen during that 12-hour period: meltdown of
> the pots,
> certainly. But what about the hard brick of the kiln interior;
> exterior;
> for that matter what about the whole building? One person said
> that nothing
> would happen because the temperature is no longer rising. But
> several of
> us felt that the residual heat could be a major problem.
> Just curious. Anyone have an informed idea? (Or uninformed, for
> that matter.)
> ---Gail
>
> Gail Dapogny
> 1154 Olden Road
> Ann Arbor, MI 48103-3005
> (734) 665-9816
> gdapogny@umich.edu
> http://www.silverhawk.com/ex99/dapogny (single historical photo -
> no longer
> registered with Silverhawk)
>
__________________________________________________
Do You Yahoo!?
Yahoo! Games - play chess, backgammon, pool and more
http://games.yahoo.com/
Earl Brunner on tue 23 apr 02
I can tell you what happened at cone 6. When I was sick last year I had one
of the
other teachers fire the Skutts. He entered into the controller program the
20
minute soak at the end of the firing as 20 hours by mistake. The glazes
melted
better, some ran a little more but in general everyone LOVED it. With some
experiment we found that we could get nearly the same results holding it for
two
hours at temperature and we have since gone to John and Ron's firing
schedule.
If your clay matures correctly for the temperature it is not necessarily a
given
that things will melt. Certainly there will be some affects from the
extended heat
work, but not necessarily a disaster. I'm sure that some clays would have a
problem, but some won't.
Gail Dapogny wrote:
> A thought-provoking hypothetical question came up at our guild today.
> Suppose you are tending the kiln and it is close to the end of a full day,
> 13 hour, cone 10 gas reduction firing and you're soaking: temperature is
> holding at about 2290 f; you lose consciousness or die or something, and
> nobody discovers the kiln (still firing/soaking) for another 12 hours.
> ....What would happen during that 12-hour period: meltdown of the pots,
> certainly. But what about the hard brick of the kiln interior; exterior;
> for that matter what about the whole building? One person said that
nothing
> would happen because the temperature is no longer rising. But several of
> us felt that the residual heat could be a major problem.
> Just curious. Anyone have an informed idea? (Or uninformed, for that
matter.)
> ---Gail
>
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Snail Scott on tue 23 apr 02
At 01:19 AM 4/23/02 -0400, you wrote:
>...
>13 hour, cone 10 gas reduction firing and you're soaking: temperature is
>holding at about 2290 f; you lose consciousness or die or something, and
>nobody discovers the kiln (still firing/soaking) for another 12 hours.
>....What would happen during that 12-hour period...
Eventually, the heat-work being done to the pots
might cause overfiring of any claybodies that were
close to their limits already. That may be fewer of
them than you would imagine, though. A long wood-
fire can last for days and be around ^10 or higher
for a whole day or more, but many nominally ^10
clays do just fine in these firings. 12 hours is
fairly trivial, really. The most obvious effect
would probably be seen on the glazes, some of which
might get runnier, and some of which might become
more variegated. It depends on the types of glazes,
though.
Note, though, that this assumes a level temperature.
This is not a plausible reflection of reality. Kilns
need constant adjustment to compensate for changing
atmospheric conditions and (sometimes) fluctuating
gas-line pressure. It's unlikely that a kiln set to
soak would stay there if unattended. It could cool
off or actually rise in temperature, depending on
conditions.
-Snail
Michael Wendt on tue 23 apr 02
I have done the overfiring error. When I first started, the kiln I used was
in the same room I worked so I threw during the day and fired at night with
alarm clocks. One night, the alarm went off and I turned it off but didn't
get up. The kiln was on full and ran all night. The next morning, when the
sun came up I screamed, $@#%!, ran out and shut it off.
The next day, I unloaded and was very sad. ALL the shelves had sagged into
"U" shapes. Cone 12 was a puddle as were cones 10 and 11. Shelves sagged
until they reached the tallest pots below and then used them for support so
they were all stuck together.Oddly, the smaller pots were fine even
overfired by several hours as long as they were covered with my oatmeal mat
glaze, although they were a very shiny finish. I still have those pots 27
years later and in use daily. The rest of the glazes ran down and stuck the
pots to the shelves, ruining both.
The brickwork came through undamaged, but I built my kiln from AP Green
G-2600 IFBs so the conclusion I reached was the flame temperature is not hot
enough to melt the brick under normal firing conditions because they leak
too much heat ( see Kirchhoff's Law, CRC Handbook ...heat radiated= 4.88
X10^-8 kcal/m^2 X T^4) . The key factor here is that a body gives off
radiation at a rate proportional to the temperature (in absolute degrees
Kelvin)to the fourth power so they leak faster and faster as they get
hotter.
No studio damage either, but they hood and the walls were all designed
according to the building codes.
Bottom line... Don't do it, you'll be sorry.
Regards,
Michael Wendt wendtpot@lewiston.com
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
Gail wrote:
A thought-provoking hypothetical question came up at our guild today.
Suppose you are tending the kiln and it is close to the end of a full day,
13 hour, cone 10 gas reduction firing and you're soaking: temperature is
holding at about 2290 f; you lose consciousness or die or something, and
nobody discovers the kiln (still firing/soaking) for another 12 hours.
....What would happen during that 12-hour period: meltdown of the pots,
certainly. But what about the hard brick of the kiln interior; exterior;
for that matter what about the whole building? One person said that nothing
would happen because the temperature is no longer rising. But several of
us felt that the residual heat could be a major problem.
Just curious. Anyone have an informed idea? (Or uninformed, for that
matter.)
---Gail
Jeff Tsai on wed 24 apr 02
Over firing is a possible problem, but more needs to be known about the kiln
and what is in it.
Most commercially built gas kilns, like geil or alpine, are made of brick
that couldstand that long soak and probably go to cone 13 without too much
more damage. But if you built your own kiln, well, the price difference
between kiln brick is based in part on how strong and durable it will be
from
continual exposure to high temperature...so it depends on the brick as to
how
that will be hurt.
Usually, a long soak on a computerized kiln will not hurt anything badly
because if it is on soak, the temperature won't go too much higher cause the
computer will adjust to keep it the same temperature. The glazes of course
will melt more, so expect more running on runny glazes, more gloss on all
the
glazes, even the matte ones, especially glazes that are matte because they
are glazes that are underfired and not because of crystal growth.
Some kinds of kiln shelves will sag more, others can probably stand the
temperature. Well made silicon carbide shelves probably won't sag suddenly
because of the high temperature being held so high, but they will sag a bit
more.
Mullite shelves will probably go bye bye, but I doubt many people use them
in
cone 10 reduction.
If you're soaking in a manual kiln, well, I don't know for sure, but I'd
assume, unless the soak was just perfect, that the pressure built up in the
kiln would just keep increasing raising the temperature further and
further....you'd then see a lot more running. high fire clays will begin to
melt...porcelains will probably go first, then Bee-mix, then those other
stonewares.
However, most anagama firings reach cone 12 in the front, and often it stays
at cone 12 and goes up to even cone 14 in the front while you spend a good
day or more trying to get the back of the thing to heat up too, Lots of
runny
glazes near the front of the kilns in that, but I've seen most stonewares
stand up to the cone 13-14 test without much warping.
Don't know what else might happen, and only half of what I've said is based
on actual first hand experience. (I left many a kiln on too long,
computerized geils, manual updrafts, globars, electrics, etc.) The rest I
just made up...no just kidding, the rest is what I've heard and can figure
out based on my many accidents.
-jeff
| |
|
