Rikki Gill on sat 4 mar 06
Last Wednesday I fired my Olsen updraft kiln, in what intended to be a cone
11 firing.
After the kiln reached the point where I could see inside [probably cone
012, I realized the higher end
[cones 8,9,10,and 11] cone pac had exploded. I thought about aborting the
firing, and then decided
that since I also use a pyrometer, and keep detailed notes of the
temperatures, I should be okay.
I was okay, until somewhere in the range of cone 7-8 the pyrometer went
crazy, and even the centigrade went OL.
I continued to fire, but had to rely on my guess work. After a 36 hour rest,
when I opened it, it was underfired. The only glaze
that looked fine was shino. Those pieces look fine, and the clay looks
vitrified. I think it must have fired to about cone 9,
maybe a little higher. My white matt was dry and ugly.
I looked at all the pieces, and replaced them in the kiln. I added a bit of
copper red to some. I am now glazing some more pieces
to replace the shino [they are fine] and plan to refire tomorrow. I talked
to Axner [T. Robert] and removed about an inch of wire from the
thermocouple unit. I think the kiln pac blowup was a fluke, made a new one,
so that should be okay. I fire with just one cone pac, because I use the
only other spy hole for the pyrometer.
What I wonder is, since this is a refiring, should I only go to cone 10?
and cone 10 bending, rather that flat 11, which is my personal choice?
I have 12 dinner plates on the bottom [hottest part] of this kiln. plus
some other flat pieces. I don't want to lose more than I have to, but I
want a
good firing with the best possible color. Would lighter reduction help in
any way? This last firing was pretty heavy.
Thanks for your consideration,
Rikki Gill
www.rikkigillceramics.com
Dave Finkelnburg on sat 4 mar 06
Rikki,
As you seem to be suggesting, if your clay and
glaze are already partly sintered and melted, then you
don't need as long to finish the job as if it were not
a refire.
However, when you are firing for clay body
vitrification the temperature you fire to is more
critical than the cone. So you still need to get to
your usual peak firing temperature, whatever that is,
to have the same level of vitrification in your clay
body.
It is not possible to say what ramp rate to use or
the soak, if any. I suggest somewhat less than
normal...you know...about the right amount...but not
too much! :-) Sorry, but since you don't know
exactly what the ramp and endpoint were last firing
you'll just have to wing it...and if you put new,
unfired ware into the kiln, to get that right you're
pretty much going to have to fire the load with your
normal ramp, peak and soak, right?
I hope this firing turns out well!
Dave Finkelnburg
--- Rikki Gill <> wrote:
> Last Wednesday I fired my Olsen updraft kiln, in
> what intended to be a cone 11 firing.
> After the kiln reached the point where I could see
> inside [probably cone
> 012, I realized the higher end
> [cones 8,9,10,and 11] cone pac had exploded. I
> thought about aborting the
> firing, and then decided
> that since I also use a pyrometer, and keep detailed
> notes of the
> temperatures, I should be okay.
> I was okay, until somewhere in the range of cone 7-8
> the pyrometer went
> crazy, and even the centigrade went OL.
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Dannon Rhudy on sun 5 mar 06
cone pac had exploded. I thought about aborting the
> firing, and then decided
> that since I also use a pyrometer, and keep detailed notes of the
> temperatures, I should be okay............
Rikki, you MAY be ok to refire to your normal temp/cone. It depends in part
on the glazes. Matte
whites are going to be ok, in general, and they may
not smooth out if you fire to a lower cone, even on
a refire. It's a toss-up - look at the newly glazed
pieces, matte or gloss? You're going to have to do
a bit of informed guessing. You know your glazes.
regards
Dannon Rhudy
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