Cindi Anderson on wed 2 jun 04
implications?
Hi Mark
Most of the heat work happens during the last 200-300 degrees. So if a kiln
shuts off very low, like 1000 degrees, you can usually just start over as if
it were never fired. Of course bisque is easier because the range is very
broad. The most common range is Cone 010 to Cone 04.which is pretty braod
Then there are the people who don't bisque at all (single firing.).
It seems to me there are two main reasons to bisque to normal bisque
temperature. One is so the piece doesn't fall apart when it absorbs glaze.
It sounds like your pieces won't do that. The second reason is to burn out
the impurities in the clay so they don't come out during the glaze firing
and cause problems. Firing slowly works well to burn out these impurities,
so maybe you are ok on that front too. Or maybe your clay doesn't have many
impurities so that would not be a problem.
You might test 1 piece with your normal glaze and make sure you are happy.
If your bisque is less fired than usually, it will absorb more glaze so you
might have to make an adjustment to your glaze thickness to get the results
you are used to.
Cindi
Fremont, CA
Mark Potter on wed 7 jul 04
implications?
Dave - Thanks much for this message. I think I may have overlooked it,
if I did please forgive the late thanks. Your explanation is much the
best of all that I received from this querie - It's amazing to me how
much of a range the 'heat work' aspect of melting really does play a
role. I'm now out trying to figure out the re-engineering of my
thermocouples on my Coneart kiln. Best regards, Mark Potter
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Dave
Finkelnburg
Sent: Wednesday, June 02, 2004 12:58 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Failure to reach temperature on bisque - what are the
implications?
Mark,
You will got lots of good responses on this.
Basically, a cone measures time exposed to temperature, sometimes
called
"heat work." The longer you leave the ware at 840C, the higher the cone
it
will be fired to, within reason. You won't get cone 10 down that way,
but
instead of cone 014, you probably fired to at least cone 012, maybe 010.
You probably have what is called "soft bisque." So...if you handle the
pieces carefully...you're good to glaze...and fix the elements. :-(
If you look at charts of temperature versus cone, they are always
stated
in degrees temperature rise per hour. At 300-C/hour temperature rise,
840C
is not as high a cone as at 150-C/hour rise. There has been more time
for
the ware to accumulate heat work with the latter, slower firing rate.
Regards,
Dave Finkelnburg
----- Original Message -----
From: "Mark W. Potter, Jr."
Sent: Wednesday, June 02, 2004 8:34 AM
....> b) Then miraculously after opening the kiln - the
> ware appears sufficiently bisqued to be able to glaze. I'm
> assuming that my chart is correct, ie. Cone 06 is around 980
> C. How the heck? I did let it cook at 840 C for a LONG TIME!!
> Many hours! Could my thermocouple be giving me incorrect
> info, or is the bisque temperature range really that broad?
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