Dolita Dohrman on wed 2 jul 08
I just wanted to share this with those of you who think that if your
kiln is programmable, you can do away with using cones. I was firing
a week before my studio sale (of course). Checked the kiln in the
morning and it seemed to be doing fine, right on schedule. Sat down
to have my coffee, then went out to check it again. Once it starts
nearing 2100 I check it often and make sure each thermocouple is
reading the same. Discovered the middle one was about 40 degrees
behind, the top was lagging slightly behind the bottom. As I was
checking this, I got an error message. So I am frantically reading
through the kiln manual and figured that if I normally soak at peak
for 20-30 minutes, then what would prevent me from soaking close to
2100 for as long as it takes to get to temperature? I would have
lost the load had I not had cones in the kiln. Sure, maybe I could
order new elements, fix it, and fire it again but not in time for my
sale. I would not have been able to tell if I was under-firing or
over-firing. The fact I had cones in there enabled me to soak that
kiln for 7 hours and not lose one pot (well, that is not true, I lost
one 'cause the lid fused to it, it is in my garden now). The glazes
looked fine and even got some racers. Who would have thought! One
interesting observation is that I had no warning my elements were
about to go out. The kiln had been going to temperature in
approximately the same amount since its installation. I learned many
things from this firing but the most important lesson was....never
fire without cones!
Dolita
John Post on wed 2 jul 08
Just to second what Dolita said about cones, I have a small little aim
test kiln hooked up to a computer controller. It really makes testing
glaze ideas happen very quickly, I wish I had purchased it sooner.
I was using cones and it was firing to cone 6 at 2200 degrees on the
computer like clockwork. I stopped using cones in a firing or two and
noticed the results were changing. I went back to using cones and
have since noticed that sometimes cone 6 is 2180, sometimes it's 2195
and sometimes it's 2205. So either the thermocouple is wandering a
bit, (it's fairly new so I doubt it) or the small little loads that go
in there vary in mass and volume enough to have an effect on the final
temperature.
Like all of my electric kilns, I have drilled out the peephole on this
one so that it is an actual 1 inch in diameter instead of tapering
towards the inside of the kiln. I'll put up a picture of this little
kiln on my cone 6 webpage for tomorrow.
John Post
Sterling Heights, Michigan
:: cone 6 glaze website :: http://www.johnpost.us
:: elementary art website :: http://www.wemakeart.org
Ric Swenson on thu 3 jul 08
Pyrometric Cones measure "heat work" (time and temperature and resultant fusing of glazes, etc).... BUT a thermocouple measures ambient temperature only. For the potter....there is a difference.
I always use cones and look at the thermocouple reading simply as a warning that the temperature in the kiln is reaching my goal.
Glad your story had a happy ending!
My 2 cents.
Happy potting!
Ric
snip> > I just wanted to share this with those of you who think that if your> kiln is programmable, you can do away with using cones. I was firing> a week before my studio sale (of course). Checked the kiln in the> morning and it seemed to be doing fine, right on schedule. Sat down> to have my coffee, then went out to check it again. Once it starts> nearing 2100 I check it often and make sure each thermocouple is> reading the same. Discovered the middle one was about 40 degrees> behind, the top was lagging slightly behind the bottom. As I was> checking this, I got an error message. So I am frantically reading> through the kiln manual and figured that if I normally soak at peak> for 20-30 minutes, then what would prevent me from soaking close to> 2100 for as long as it takes to get to temperature? I would have> lost the load had I not had cones in the kiln. Sure, maybe I could> order new elements, fix it, and fire it again but not in time for my> sale. I would not have been able to tell if I was under-firing or> over-firing. The fact I had cones in there enabled me to soak that> kiln for 7 hours and not lose one pot (well, that is not true, I lost> one 'cause the lid fused to it, it is in my garden now). The glazes> looked fine and even got some racers. Who would have thought! One> interesting observation is that I had no warning my elements were> about to go out. The kiln had been going to temperature in> approximately the same amount since its installation. I learned many> things from this firing but the most important lesson was....never> fire without cones!> Dolita
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