search  current discussion  categories  kilns & firing - misc 

kiln firing too long...

updated sat 16 mar 02


Alan Stewart on fri 15 mar 02

Morning, All,

This isn't really how I wanted to start participating in this list:
introducing myself and asking for help almost in the same breath. And the
truth is, I'm having a problem with the kiln.

It's an Olympic oval kiln, with a downdraft kiln vent and an electronic
control but no kilnsitter. We ran our first firing earlier this week, using
a predefined slow glaze program set to ^6. The kiln was relatively loosely
filled, mostly with pieces made from Lizella, a local Georgia clay that I
love and have used frequently; it fires to a dark, warm red at ^6. Some
pieces were glazed with high-fire (^6) commercial glazes, and some weren't.
The kiln vent was running the entire time.

The manual says that the slow glaze program should run for about seven hours
going to ^04, and that the times for a ^6 should be the same, with only the
end temperature varying.

Well, the firing ran 14 hours, and reached 2183F before shutting off. When
we removed the pottery at about 200F, many of the pieces had darkened,
apparently singed or burned spots. The glazes had all pretty much been
burned out. The clay itself was a VERY dark red, and seemed in many places
to have a blue-black sheen.

>From what I can tell, the end temp is in line with a ^6 firing, and the
thing simply ran on for twice the scheduled time, burning out the glazes and
singeing the clay itself.

I've copied the manfacturer on this e-mail, and I know Rob from Olympic
subscribes to this list; I'm going to call him today and see if he has
anything to say.

In the meantime, has anybody had a similar experience with their
kiln/controller? Any ideas as to why it would run 14 hours when the program
is set for half that time? From what I can see, if I can't trust the
controller, then I can't fire the kiln either safely or productively. NOT
where I want to be right now as we start into production...

On a more positive note, I just finished a drape-mold Lizella platter that
I'm very happy with: wide, burnished rim with a textured interior. I draped
it over a pie plate on which I'd mounted several stones. The resulting lumps
and humps, in conjunction with the texturing I did, remind me of water
rushing over river stones. It's drying, and if I can get the kiln figured
out, maybe I can even fire it.

So, I'm off to telephone Olympic and see what they know. Then it's back to
making things I like...

More later,

Alan Stewart
The Clay Lizard Studio
4358-A Southside Dr.
Acworth, GA 30101