Maurice Weitman on wed 6 sep 06
At 22:08 -0400 on 9/6/06, Tom Witman wrote:
>[...] Could you look at the photo and tell me
>if I am close or do I need to add offset to my controller? What compounds
>the problem is that I do a 20 minute soak at Cone 6 and then do a slow
>cool down pausing again for 20 minutes after a 100 degree drop. I see a
>slight bend in the Cone 7 cone, but don't know if this is normal with the
>20 minute soak.
Hello, Tom,
The following is my opinion; others will offer theirs, I'm sure, but
here goes...
You don't say what number the cones are; I will assume they're 5,
6,and 7, r to l.
If the 5 and 6 cones not self-supporting as is 7, I'd suggest you use
one type consistently. I prefer the self-supporting cones for their
consistency and lack of need for support (which adds another variable
-- if the cones are not at the correct angle in the packs, you risk
an inaccurate/inconsistent result).
The slight bend you note in 7 is fine for a cone 6 firing. The cone
6 touching would indicate that you fired to a full cone 6. (If this
were a self-supporting cone, it would be beyond the target cone.)
These results would indicate to me that your controller (**the way
you use it**) is adjusted and programmed just fine. The soaks and
slow cool-down are not problems; they are how you've decided to fire
to get the results you want. And the way you've programmed your
controller and offsets seems to be fine.
But I think the more important question is how'd your firing go (for
the pots)? Are you happy with the results? I think witness cones
are wonderful for repeatability and to note variations in different
parts of the kiln or with different stacking methods, but they should
not be the objective. Your happiness with how your pots fired should
be what you measure. Some glaze/body combinations might be better
with 6 as flat as your 5, or as soft as your 7.
I hope that's helpful.
Regards,
Maurice
ps Notice I didn't say anything about how you've misspelled your name.
Tom Witman on wed 6 sep 06
I'm guessing with the server being down this weekend that my message
didn't get through since I haven't seen it yet.
A while ago I had a glaze problem and Rob asked if I had used witness
cones to verify that my controller was working correctly to reach Cone 6.
I did another firing and put cones in and I put the photo of them on
www.pensandcalls.com/cones.jpg. Could you look at the photo and tell me
if I am close or do I need to add offset to my controller? What compounds
the problem is that I do a 20 minute soak at Cone 6 and then do a slow
cool down pausing again for 20 minutes after a 100 degree drop. I see a
slight bend in the Cone 7 cone, but don't know if this is normal with the
20 minute soak.
Any help will certainly be appreciated.
Tom
John Rodgers on thu 7 sep 06
Tom,
From my perspective you have an apples and oranges mix with your cones
in the picture. In discussions with Arnold Howard at Paragon about my
kilns, it was made clear to me that there are differences enough in the
two types of cones you show in the picture that you do not want to mix
them to do any kind of measuring. Use all of one kind or the other but
not both together when measuring heat work. They do bend at different
rates and having the two types mixed together the way you have leads to
a misinterpretation of what is happening. Use all of only one kind of
cone or all the other kind and do another test. I would expect your
guard cone will react differently. In fact, to really get a good image
of what is happening, for your test use three of the free standing
cones, and three of the type set in a clay base. Place two 5 cones side
by side, two 6 cones side by side and do the same with the two 7 cones.
Compare the differences when the firing is complete.
As for the soaking - if you soak at cone 6, the soak will take you
towards the next cone - 7 - due to heatwork over time without an
increase in temperature. So a 7 cone will bend to some degree as a
result of the soak. How much of a bend depends on how long the soak.
Best of success with this.
John Rodgers
Chelsea, AL
Tom Witman wrote:
> I'm guessing with the server being down this weekend that my message
> didn't get through since I haven't seen it yet.
> A while ago I had a glaze problem and Rob asked if I had used witness
> cones to verify that my controller was working correctly to reach Cone 6.
> I did another firing and put cones in and I put the photo of them on
> www.pensandcalls.com/cones.jpg. Could you look at the photo and tell me
> if I am close or do I need to add offset to my controller? What compounds
> the problem is that I do a 20 minute soak at Cone 6 and then do a slow
> cool down pausing again for 20 minutes after a 100 degree drop. I see a
> slight bend in the Cone 7 cone, but don't know if this is normal with the
> 20 minute soak.
>
> Any help will certainly be appreciated.
>
> Tom
>
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Tom Witman on thu 7 sep 06
Thanks to the group!
One thing is certain - 'use the same type of cone'. :o) Unfortunately,it
was 'take what we have' at the store so I did the best I could. I did
make certain that the bases of all cones were flat to the shelves.
The program I use was garnered from the web several years ago and has
always given me good results except for porcelain dishes, but I gather
from other discussions that this is no surprise.
I had mixed one green glaze that gave me a lot of large blisters and the
feeling on the group was that I was not firing high enough. Other glazes
in the same batch AND on the same piece, even, looked good. I just wanted
to check the max temp. From the answers, it sounds as if my temperature
is in the ballpark. I will get all self supporting cones as suggested.
Thanks
Tom
Snail Scott on thu 7 sep 06
At 10:08 PM 9/6/2006 -0400, Tom W wrote:
>...I do a 20 minute soak at Cone 6 and then do a slow
>cool down pausing again for 20 minutes after a 100 degree drop. I see a
>slight bend in the Cone 7 cone, but don't know if this is normal with the
>20 minute soak.
Heat work is heat work, whether it occurs during
'firing' per se, or during a soak. The cones will
tell you true. The pyrometer, unfortunately, won't.
It can't detect the added heat work of the soak,
but only increases (or decreases) in temperature.
(You know this, I'm sure; I'm just being pedantic.)
If the cones say 'almost ^7' after the soak, then
it's almost ^7.
If you principal concern is simply to have a well-
calibrated pyrometer, and the soak is making it tough
to check the equivalency, do a straight-up firing
without the soak (empty, if need be) just to check
it.
My opinion: who cares whether the pyrometer is set
for some specified temperature equivalent of heat-
work or cones? Figure out what setting works well
and use it. I don't understand this obsession
people have with making their firings come out
exactly to ^6, or ^9 or whatever. I seriously
doubt that anyone's clay or glaze is optimized so
precisely to that arbitrary referent. It's more
likely to be ^6-and-a-smidge, or not-quite-^9,
or something else that doesn't happen to sit
squarely on a cone number. Fire to suit the
materials, not the numbers.
Cone numbers and their temperature/time equivalents
are referents, nothing more. Not like lines in a
parking lot that you've got to position yourself
in a precise relation to, or face a fine from the
Firing Police!
-Snail
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