Christopher Anton on mon 2 oct 00
When you say you put a small cone in the sitter, are you using a bar "cone"
or a small pyramid type? If you are using a "small cone" (pyramid), then
placement will be critical since the (minimal) pressure of the bar may be
applied to different thicknesses. I was taught to use a bar "cone" for
sitters for this reason.
- Chris
Cat Jarosz on mon 2 oct 00
Hi CAT ... I dont personally know the answer to that one and wont
dignify a guess without the cone chart in front of me... but I bisque in an
electric kiln and find that the self supporting large cone ^05 is
starting to go down when my small ^04 thats in my kiln sitter goes
off.... I'd say at the 2 o/clock postition ... I just checked the
difference in temps from the charts for orton standard cones and there
is a 36 degree difference from 05- 04 and a 38 degree difference from
6-7 ... thats only a 2 degree difference so I'd guess that if your
using the self supporting cones that your large 6 would be around 230
maybe the 3 0clock position when your small 6 is shutting off the kiln...
hope this helps some ... the other CAT >^..^<
Snail Scott on mon 2 oct 00
At 05:53 PM 10/2/00 -0400, you wrote:
....
>I opened the kiln and found grossly over-fired work. Considering that the
>Orton cone box stated that the large cones were the most accurate, and that
>the clay I am using is designed for ^6, how am I getting bloating and burnt
>glazes. Most importiant, why is a ^7 sitter shutting my kiln off 2 hours
>before a visual ^6??????
>
....
I also fire to ^4-6 electrically. I usually (depending on the speed of the
firing)
figure on a 1 1/2 or 2 cone difference between the sitter and the visual
cones.
Some of my glazes I fire according to the sitter cone (lo-fire commercial
ones,
for example) but if I need a solid ^6 (for instance) I'll put a ^8 in the
sitter,
mainly as a failsafe. The large cones _are_ more accurate. It doesn't
matter, though,
what the nominal 'cone' of a clay or glaze is, or whether it matches the
number on
the cone you used. Use the cone that gives the result you need.
If the sitter ^7 gives the result you want at a speed you like, put a pack
of cones,
say, ^3,4,5, in with the next firing. It doesn't need to be in front of a
peephole.
Just inspect it when you unload. The cone that's just bent is your new
visual cone #!
Sitter cones are tiny, and respond more quickly to temperature increase
than large
cones. That is why the discrepancy is greatest with fast firings. (You may
notice
that charts which list the temperature rating of each cone do so with a
correlation
to the _speed_ of increase. This is because cones don't measure just
temperature,
like a pyrometer, but also 'heat work', which is a closer indication of
what's
actually happening to your clay as it vitrifies.)
Don't put too much emphasis on the the clay manufacturer's rating; If it's
overcooked at a
fastfired visual^6, then it is. If you like the clay otherwise, just figure
out which cone
will tell you when it's vitrified and use that one, whatever number it
happens to be.
Don't sweat the numbers!
-Snail
Cindy Strnad on mon 2 oct 00
Hello, Cat.
Maybe the fact that you have the #6 cones sitting in front of the peep holes
is keeping them cool longer than they should be. You might try moving them
to the back of the kiln and keeping a clear line of sight. In a smaller
kiln, this can be a factor. I do this even in the larger kilns, though. I'm
guessing you're using a smaller kiln than you're accustomed to, since you're
switching over from gas to electric--that could be one difference in your
cone behavior.
If a #7 cone in your kiln sitter gives you the results you want, then use
it. If I want to fire my small kiln to a true ^6, though, I need a #8 cone
in the sitter. I know it's only supposed to be one cone difference, but I
haven't found that to be true in my case. Could be my mile-high altitude
makes a difference, though.
You didn't mention what sort of controls your kiln offers. Mine has only
manual switches--five of them--and they're either on or off. That's it. I
usually fire glaze with only 4 elements. I alternate which elements I use to
give them all a turn at bat. This slows down the firing a bit. It's still
faster than my larger kilns, but not as fast as it would be at full power.
Hope this is of some help to you,
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
www.earthenvesselssd.com
Cat Audette on mon 2 oct 00
Help.
I recently switched to ^6 electric. I tested about 30 glazes, putting a
small ^6 cone in the cone sitter. Fired the kiln (a little faster than I
expected) and got ok results. Lots of pinholes. From that I adjusted the
glazes, added color and retested to ^7 with just the cone sitter. Again a
real fast firing but I was happy with the results.
Yesterday I loaded a full load, put a ^7 in the sitter and large ^6 cones at
every peep. Fired the kiln. It shut off in record time, but every ^6 was
standing straight up. I though maybe the cone in the sitter was acting funny
so I turned it back on and let it roll till the large ^6's were at least
tipping. It took at least two hours.
I opened the kiln and found grossly over-fired work. Considering that the
Orton cone box stated that the large cones were the most accurate, and that
the clay I am using is designed for ^6, how am I getting bloating and burnt
glazes. Most importiant, why is a ^7 sitter shutting my kiln off 2 hours
before a visual ^6??????
To make sure that I have an even firing, what cone do I put infront of the
peeps if Im still going to put a ^7 in the sitter??
Frustrated.
I have a show in 5 days.
Ugh.
--
Cat Audette
cataudette@earthlink.net
"Clay is the way"
Paul Gerhold on tue 3 oct 00
Dear Frusterated
Been doing electric kilns for ever. Here are some things to think about.
1.There are a lot of adjustments on a kiln setter. You can change firings
several cones just by playing around.
2.The way you place the cone does make a difference
3.I don't care what the cone guru's say-the weight of ware in the kiln does
influence the cone at which the glazes develop properly..
4.Slower firings do in general yield better results. Speed of firing will
change temps at which glazes mature.
5.The relationship between glaze results on test tiles and actual performance
on real pieces is tenuous at best,
6.And of cource if you turn a kill back on after a period of time all bets
are closed.
My best advice is to find a firing schedule, a cone, and a degree of kiln
loading that works and stick to it.I also use a pyrometer, guard cones , and
never rely on the kiln setter to shut off the kiln.Electric firing is a bitch
too.
Good luck
Paul in the woods
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