Jim and Judith Enright on fri 10 apr 98
------------------
Well, I know it just had to happen -- in the final stages of preparing for
Open Studios next weekend and the ironworker who makes the table frames for
my inlaid tiles tells me the latest set is 3 days behind schedule AND the
tables have to go back in the shop for 2 days for final finishing after the
tile is laid. So in one minute I've lost 5 days and I'm wondering how this
is mathematically possible.
SO, have to rush those tiles through their firing process. This batch of
30 1/2=22 thick tiles was cut 2 1/2 weeks ago and was not completely dry. I
usually allow a month drying. ANYway, two nights ago I load the (electric)
kiln, candle overnight and proceed with the normal =5E04 bis=A6ue firing
schedule of about 7 hours. After switching to medium, I take off for work.
The timer was set to shut off the kiln 3 hours later, but I expected the
cone to go down after 1 1/2 hours on high, which is normal. Got home last
night to discover that the kiln had been churning on high for the entire 3
hour period, and only shut off when the timer clicked. I had nightmares
about overfired bisque, no tables, alternative surface treatments, the
whole bit. Plus the kiln was REALLY hot, so much so that I unplugged the
darn thing. This morning I unloaded and found the sitter cone barely bent.
No senior cones in place this firing, so I really don't know how hot it
got. On the other hand, everything looked fine and I ebulliantly thanked
the kiln gods for the bisque dust and softish texture of the tiles.
Now then, what could have happened? I'm thinking any number of things:
the tiles really needed the extra time to get a mature bisque=3B the cone =
was
a dud=3B the elements are aging (I've done less than 100 firings in my Skutt
1018 over the past 4 years, mostly bisque at =5E04 and glaze at =5E6, with
about 5 =5E10 firings in past month)=3B the sitter needs adjusting.
Any ideas, comments, jokes are heartily appreciated. (Those tiles are now
getting their glaze firing and I'm keeping a close eye on the kiln.)
Be well.... and thanks=21
Judith Enright =40 Black Leopard Clayware
email: BLeopard=40ricochet.net
gambaru on sat 11 apr 98
A suggestion: check the rod in your sitter. They do shrink/burn away over
time and therefore your sitter will not turn off as expected and usually
beyond the temp that the cone is rated, especially bisque temp and trip the
sitter earlier for glaze temp cones. Easily replaced.
MB
-----Original Message-----
From: Jim and Judith Enright
To: Multiple recipients of list CLAYART
Date: Friday, April 10, 1998 8:50 AM
Subject: Over- or Mis-fired?
----------------------------Original message----------------------------
------------------
Well, I know it just had to happen -- in the final stages of preparing for
Open Studios next weekend and the ironworker who makes the table frames for
my inlaid tiles tells me the latest set is 3 days behind schedule AND the
tables have to go back in the shop for 2 days for final finishing after the
tile is laid. So in one minute I've lost 5 days and I'm wondering how this
is mathematically possible.
SO, have to rush those tiles through their firing process. This batch of
30 1/2" thick tiles was cut 2 1/2 weeks ago and was not completely dry. I
usually allow a month drying. ANYway, two nights ago I load the (electric)
kiln, candle overnight and proceed with the normal ^04 bis&ue firing
schedule of about 7 hours. After switching to medium, I take off for work.
The timer was set to shut off the kiln 3 hours later, but I expected the
cone to go down after 1 1/2 hours on high, which is normal. Got home last
night to discover that the kiln had been churning on high for the entire 3
hour period, and only shut off when the timer clicked. I had nightmares
about overfired bisque, no tables, alternative surface treatments, the
whole bit. Plus the kiln was REALLY hot, so much so that I unplugged the
darn thing. This morning I unloaded and found the sitter cone barely bent.
No senior cones in place this firing, so I really don't know how hot it
got. On the other hand, everything looked fine and I ebulliantly thanked
the kiln gods for the bisque dust and softish texture of the tiles.
Now then, what could have happened? I'm thinking any number of things:
the tiles really needed the extra time to get a mature bisque; the cone was
a dud; the elements are aging (I've done less than 100 firings in my Skutt
1018 over the past 4 years, mostly bisque at ^04 and glaze at ^6, with
about 5 ^10 firings in past month); the sitter needs adjusting.
Any ideas, comments, jokes are heartily appreciated. (Those tiles are now
getting their glaze firing and I'm keeping a close eye on the kiln.)
Be well.... and thanks!
Judith Enright @ Black Leopard Clayware
email: BLeopard@ricochet.net
Ron Roy on sat 11 apr 98
------------------
Hi Judith,
The moral of the story is - never, ever, trust a kilnsitter and always have
at least one large cone that you can see in each firing.
We used kiln sitters for years when I taught at a community college - we
only used them to warn us that the end was near - we then reset the sitter
and watched the cones go down.
I have seen one situation where a piece of clay (or was it broken cone,
kiln shelf, or furniture) which got in under the rod and stopped it from
moving enough to shut off. Rods can bend, get caught on a shelf, contacts
can weld closed - and god knows what else.
I use a controller now and I don't trust that either - yet. I like to be
there and watch the cone go down - there are just too many variables to
leave kilns alone.
The other rule I ALWAYS follow - when my firing is done shut off the main
supply switch or the circuit breaker. If you don't have an interrupt on the
main line to your kiln - get one.
=3E----------------------------Original message----------------------------
=3E------------------
=3EWell, I know it just had to happen -- in the final stages of preparing =
for
=3EOpen Studios next weekend and the ironworker who makes the table frames =
for
=3Emy inlaid tiles tells me the latest set is 3 days behind schedule AND the
=3Etables have to go back in the shop for 2 days for final finishing after =
the
=3Etile is laid. So in one minute I've lost 5 days and I'm wondering how =
this
=3Eis mathematically possible.
=3E
=3ESO, have to rush those tiles through their firing process. This batch of
=3E30 1/2=22 thick tiles was cut 2 1/2 weeks ago and was not completely dry.=
I
=3Eusually allow a month drying. ANYway, two nights ago I load the =
(electric)
=3Ekiln, candle overnight and proceed with the normal =5E04 bis=A6ue firing
=3Eschedule of about 7 hours. After switching to medium, I take off for =
work.
=3EThe timer was set to shut off the kiln 3 hours later, but I expected the
=3Econe to go down after 1 1/2 hours on high, which is normal. Got home =
last
=3Enight to discover that the kiln had been churning on high for the entire =
3
=3Ehour period, and only shut off when the timer clicked. I had nightmares
=3Eabout overfired bisque, no tables, alternative surface treatments, the
=3Ewhole bit. Plus the kiln was REALLY hot, so much so that I unplugged the
=3Edarn thing. This morning I unloaded and found the sitter cone barely =
bent.
=3ENo senior cones in place this firing, so I really don't know how hot it
=3Egot. On the other hand, everything looked fine and I ebulliantly thanked
=3Ethe kiln gods for the bisque dust and softish texture of the tiles.
=3E
=3ENow then, what could have happened? I'm thinking any number of things:
=3Ethe tiles really needed the extra time to get a mature bisque=3B the cone=
was
=3Ea dud=3B the elements are aging (I've done less than 100 firings in my =
Skutt
=3E1018 over the past 4 years, mostly bisque at =5E04 and glaze at =5E6, =
with
=3Eabout 5 =5E10 firings in past month)=3B the sitter needs adjusting.
=3E
=3EAny ideas, comments, jokes are heartily appreciated. (Those tiles are =
now
=3Egetting their glaze firing and I'm keeping a close eye on the kiln.)
=3E
=3EBe well.... and thanks=21
=3E
=3EJudith Enright =40 Black Leopard Clayware
=3Eemail: BLeopard=40ricochet.net
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
VandRKatz on sat 11 apr 98
Clayart is a good place to blow off steam & frustrations. I have had simular
things happen to me - hopefully, you simply had a bad sitter cone. I must
admit that a bit excessive bisque firing has not had a dramatic effect on my
glazing - knock on wood.
Naturally, these things only occur when you are getting ready for a show. I
suggest that you put some witness cones in the next couple firings to confirm
that your elements are in good working order.
Keep on plugging & try to enjoy your show.
Good luck !
Vicki Katz
Katz Creek Pottery
Tim Stowell on sun 12 apr 98
I had a similar experience several years ago and traced it to an element.
One element in the kiln had broken where a tiny bit of glaze had landed
on it in a previous firing. Examine all of your elements and/or test them
using a multi-meter.
Tim
Tim Stowell Gerard Stowell Pottery
Stacey Gerard 290 River Street
tstwll@juno.com Troy, NY 12180
(518)272-0983 www.trytroy.org/gerard/
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The Kiln Guy on mon 13 apr 98
>After switching to medium, I take off for work.
The timer was set to shut off the kiln 3 hours later, but I expected the
cone to go down after 1 1/2 hours on high, which is normal.>
---------------------------
Hi Judith,
Were your switches set to `medium` or `high` when you left?
If they were on high, check - that all elements glow - that switches do not
cycle off when set in the high position - kiln sitter set up (unlikely as
the cone would still be bent even if set up incorrectly)
Chris @ Euclids
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