Bonnie/Jeremy Hellman on sun 6 oct 02
Hi Karen,
Overfired means the glazes got too much heat work. Could be a =
combination of time or excess heat. A controller measures temperature. =
Cones are a measure of work, which is a combination of both temperature =
and time. That's why in those cone charts the temperature for each cone =
is different depending on how quickly you fire.=20
I also fire a small 3 cu ft kiln, and if I leave it turned on long =
enough with the dials in mid range (4 or 5 out of 7) my ^6 sitter cone =
will trip and I'll get up to temperature.=20
It sounds like your kiln may also have a differential in firing between =
top and bottom shelves and the middle. Your middle is firing hotter than =
the top and the bottom. You may want to use self-supporting cones on ALL =
shelves, and maybe even on the outside of a shelf as well as the inside, =
until you learn how it fires. Also, a tightly packed kiln fires =
differently than a lightly packed kiln. The point of using cones is to =
learn how your kiln fires.=20
I used to load my kilns tightly, stuffing in as much as I could. Then I =
noticed that some glazes didn't fire as well as when I left more room =
around my pots. So I've tried to leave more room around my pieces, to =
allow all parts of all pieces to heat up evenly.
BTW not all glazes like a hotter kiln, but some do. So if loading your =
kiln a bit lighter still leaves you with the firing difference, you can =
use glazes that like it hot in the middle, and glazes that like it =
cooler on the top and bottom shelves.
Too shiny glazes are usually the result of overfiring. You also get =
color differences in overfiring.
Craters and bumps for me are when a glaze needed to be re-sieved and I =
didn't do it.
My thermocouple has gone for 90 firings, over half of which were ^6, the =
rest either ^04 or ^06, but I was told that the thermocouple would be =
the most likely thing to break so I bought a spare when I bought the =
controller. I don't remember it being expensive and it's easy to =
replace.
Bonnie
----- Original Message -----=20
From: Cliff/Karen Sandlin=20
To: candle@INTREX.NET ; mou10man@sgi.net ; 'Snail Scott'=20
Cc: CLAYART@LSV.CERAMICS.ORG.=20
Sent: Sunday, October 06, 2002 1:39 PM
Subject: disappointing kiln opening - thanks!
Thank you very much for your help. Chris, when you say overfired, do =
you mean I should not do the 30 min. hold, should not use the slow =
speed, or should not program it for cone 6? I have another load to put =
in today (mostly re-fires that have the craters dremeled smooth) and am =
wondering how to program my controller.
I DID bisque the cones and holders and they were straight up vertical. =
I won't do that again, thanks to your advice. However, previously I =
used self-supporting cone 6 and 5, and none of the cones on the top =
shelf or the bottom shelf bent more than slightly. The middle two shelf =
cones bent as they should.all the way. I do not have a kiln sitter at =
all.
Snail: Do you think the craters, bumps, and too shiny glazes would be =
due to underfiring? Chris suggested these were signs of overfiring. I =
am confused.=20
Should a thermocouple need to be replaced after only 31 firings, half =
of which were for bisque (cone 04)?
Clayart is a fabulous resource and I am appreciative.
Cliff/Karen Sandlin on sun 6 oct 02
Thank you very much for your help. Chris, when you say overfired, do
you mean I should not do the 30 min. hold, should not use the slow
speed, or should not program it for cone 6? I have another load to put
in today (mostly re-fires that have the craters dremeled smooth) and am
wondering how to program my controller.
I DID bisque the cones and holders and they were straight up vertical.
I won't do that again, thanks to your advice. However, previously I
used self-supporting cone 6 and 5, and none of the cones on the top
shelf or the bottom shelf bent more than slightly. The middle two shelf
cones bent as they should.all the way. I do not have a kiln sitter at
all.
Snail: Do you think the craters, bumps, and too shiny glazes would be
due to underfiring? Chris suggested these were signs of overfiring. I
am confused.
Should a thermocouple need to be replaced after only 31 firings, half of
which were for bisque (cone 04)?
Clayart is a fabulous resource and I am appreciative.
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