Lili Krakowski on sun 15 jul 07
Donna asks:
"Is it true that you can use only Cone 1 and up glazes on Stoneware and Cone
06 and lower glazes on Earthenware?"
Annette wants to know:
"Hi everyone! I've been having a problem with my kiln... The sitter
does not turn itself off when I'm firing to ^ 6 so I regulate it with the
timer on the sitter instead. However my ^ 6 Glazes seem to mature and come
out
looking fine. We looked at the elements while the kiln had been on high for
a
while and they all turn red but neither the bar in the sitter nor the ^ 6
witness cone bend the way they should,probably only about a quarter or a
third
way down. Any comments will be greatly appreciated! "
Ok. As the drought finally is broken and I do not need to lug water to the
garden I have all this time on my hands.
(ROFL)
Donna:
Your question is analogous to asking must I use a size 2 on a 98 lbs woman,
and size 20 on a 200 lbs one? Glazes relate to the clay body as clothing
sizes relate to the human body. Low fired/earthenware glazes are designed
and fitted to low fire/earthenware bodies, and highfired or stoneware glazes
adjusted for high fired bodies. This is a very inadequate analogy, because
the difference between low and high fired glazes and the bodies to which
they are designed and the adjustments are different proportions of alumina
to silica and the different amounts of flux etc. But the answer is NO.
Use the glazes sold or published for the temperature to which you will be
firing. Now go and read a couple of books on glaze--and you will understand
it all!
Annette:
I am truly confused. The sitter is a wonderful gismo that --this is SO
simplified I am blushing--has two flat little arms that support a junior
cone, or a bar, and a third little arm--this one round, basically a
wire--rests on the bar/cone. As the bar/cone softens from the effects of
time and heat it sags downward, tilting the wire that rests on it, which,
when it tilts enough releases the catch at the outside of the kiln,
dropping a little square of metal that in falling shuts off the switch.
Actually this is very analogous to traps where the animal, by eating the
bait, loosens something at the other end which springs a noose, or springs
a door. . I would not be surprised if, indeed, a trap of this type had
given whoever the idea for a kiln sitter.
Now the timer is another neat gadget, because it is a sort of backup, which,
like all backups, shoud be used as a backup, and not as a primary tool. To
the best of my knowledge the timer is there to prevent accidents. For
instance a pot blows up or topples in the kiln and jams the kiln sitter.
The timer, if set correctly will turn the kiln off. Or an emergency (God
forbid) calls you away and you need to turn the kiln off then and there,
and your kiln is hard-wired, and you do not want to resort to the circuit
breakers, on and on, so you turn the kiln off on the timer.
As is said oh-so-often on Clayart, the timer is not meant to fire the kiln
for you!!!
Ok. You say the sitter does not turn off the kiln, nor do the cones bend
properly. That means the kiln has not reached c.6!
Why do you assume the timer does it? Why do you not let the kiln fire till
the cones bend properly and the kiln sitter "drops"? You seem to be firing
by time/hours....Why? When you look at a baking recipe you will see that it
generally says: "Bake for 25-30 minutes, or till top is a golden brown. "
Why do you suppose it says that? Because ovens fire differently, even
electric ovens are affected by voltage drop. Size of oven, where the baked
good sits and so on affect the baking.
By the way the reason your glazes look okay is that normally glazes have a
two, three-cone range. The reason for THAT is that not all kilns fire
alike, and in large fuel burning kilns there are cooler and hotter spots.
Fuel burning experts will know exactly where in their kilns is ideal for a
particular glaze...
So. Donna, Annette: It is deep breath time. Go to the library get a bunch
of books on pottery, try to get Cooper's book Electric Kiln Pottery. It is
blindingly costly on the second hand market, why it is not being reissued I
do not know, BUT a library may be able to get it for you. However there are
many books on pottery that explain what you are puzzled by. Go and learn.
Lili Krakowski
Be of good courage
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