Gay Judson on sun 7 jan 07
Lili's comments touch on a question that has been building up in my mind.
If I am using the Orton cones and I get a cone 6 'touching' but my highest
temperature was 2185 have I fired my glaze to cone 6? When I was trying to
find the cause of my pinholing problems frequently I was told I was
underfiring because I programmed my kiln to go only to 2185 and not higher.
But I had a short soak and a longer hold on the way down. I assume that
the time was giving the equivalent of a full cone 6 even at the lower
temperature and I thought that the cone pack gave the true evaluation. But
because of the reactions I got from others I have begun to question my
assumptions.
Thanks, Gay Judson in San Antonio, TX
John Hesselberth on mon 8 jan 07
On Jan 7, 2007, at 9:40 AM, Gay Judson wrote:
> If I am using the Orton cones and I get a cone 6 'touching' but my
> highest
> temperature was 2185 have I fired my glaze to cone 6? When I was
> trying to
> find the cause of my pinholing problems frequently I was told I was
> underfiring because I programmed my kiln to go only to 2185 and not
> higher.
Hi Gay,
The person that told you this doesn't understand that cones are much
more accurate than thermocouples. And yes the soak and slow cool does
make a difference. Thermocouples also drift over time. Every few
firings I will have to adjust my peak thermocouple temperature by 3
or 4 degrees to keep the cones falling the way I want them to. Cones
are the "gold standard". Thermocouples are only approximate because
of the drifting and varying heating/soaking conditions.
Regards,
John
Snail Scott on mon 8 jan 07
At 09:40 AM 1/7/2007 -0500, you wrote:
>If I am using the Orton cones and I get a cone 6 'touching' but my highest
>temperature was 2185 have I fired my glaze to cone 6?
If your cone was properly placed, then
you did reach ^6. The temperature
readout is moot. It may be that your
glaze really needs more like ^6-1/2 or
so.
-Snail
Dave Finkelnburg on mon 8 jan 07
Gay,
IF the #6 witness cone you put in the firing bent
to the tip just touching, you fired to cone 6 (even a
little past, according to Orton). The appearance of
cones at the end of the firing is what determines the
cone fired to. Temperature is an indication, but only
that.
Cones bend by "creep" which is the effect of
gravity on the cone material as it softens when it's
hot. Creep takes time, and heat, as you obviously
understand, but whether the combination of time and
temperature in your kiln achieves a certain cone can
only be measured by a cone exposed to that firing.
The rest of us may have opinions, but only the
cones know for sure! :-)
Dave Finkelnburg, chuckling after reading the
subject line of Lili Krakowski's post, "Splitting
hares..." You have to love a literate wit!
--- Gay Judson wrote:
> Lili's comments touch on a question that has been
> building up in my mind.
> If I am using the Orton cones and I get a cone 6
> 'touching' but my highest
> temperature was 2185 have I fired my glaze to cone
> 6?
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Erik Harmon on mon 8 jan 07
Depending on which kiln your firing and what thermocouple you are using. 2185 could easily be 2200 or more, even the best thermocouples are not that accurate. How long is short?
Erik
Gay Judson wrote:
Lili's comments touch on a question that has been building up in my mind.
If I am using the Orton cones and I get a cone 6 'touching' but my highest
temperature was 2185 have I fired my glaze to cone 6? When I was trying to
find the cause of my pinholing problems frequently I was told I was
underfiring because I programmed my kiln to go only to 2185 and not higher.
But I had a short soak and a longer hold on the way down. I assume that
the time was giving the equivalent of a full cone 6 even at the lower
temperature and I thought that the cone pack gave the true evaluation. But
because of the reactions I got from others I have begun to question my
assumptions.
Thanks, Gay Judson in San Antonio, TX
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Lee Love on mon 8 jan 07
On 1/7/07, Lili Krakowski wrote:
> So if the temp you want is 1200 degrees, I assume Centigrade, (2192F) you
> are at a British c 6, a Seger cone 6a, BUT between c.4 and c.5 Orton cone.
> And Orton c.5 is 1205C/2201F. An Orton c. 6 is 1230C/2246F, and the British
> c.7 is the equivalent.
Hi Lili,
One of us must be using "Pete Seger" cones and not Hermann Seger
cones ;^) (all I can get here in Japan are Seger.)
My Seger measure a higher temp at equivalent Orton cone
numbers. For example: Seger cone 6a is 2264*F while Orton cone
6 is 2232*F . Leach's cone 8 glazes are cone 8 Seger, which are about
cone 9 Orton.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Gay Judson on mon 8 jan 07
Thanks to all who responded to my query about time/temp/cone reading. I
shall sleep better for knowing that I have understood that the cone does
tell the tale.
I am over the pinholing problems(hopefully--not because I got rid of them
but because I determined it was a problem with the clay and I have moved on
to another clay. Still I wanted to be sure I understood working with
cones--which I use faithfully in each firing--one on each level.
Again thanks for the guidance! Gay Judson in San Antonio, TX
Ivor and Olive Lewis on tue 9 jan 07
I was under the impression that Cone values apply to situations of =
rising temperature and that the actual temperature depends on the rate =
at which temperature increases. Observation of completion of firing is =
always made prior to cessation of heating. I do not cease heating my =
kilns until my cones indicate I should. The state of cones taken from a =
cold kilns just give me an indication of the consistency of my firings.
The temperature you give is for a slow rate of increase, 60 deg C or 108 =
deg F per hour. If you are firing at the higher rate the setting on your =
controller has to be elevated to 1222 deg C or 2232 deg F per hour. So =
knowing the ramp rate of your kiln is important when considering the =
solution to a firing problem.
It seems reasonable to suppose that when a cone starts to squat or bend =
it will continue to do so until its temperature falls below the melting =
point of the new compounds that are forming as that cone vitrifies, =
which might be several hundred degrees below the true maturity =
temperature.
Which raises questions about why we should hold at a specific =
temperature, cool slowly or have hold periods at lower temperatures. =
There are legitimate reasons but engaging and utilising additional "HeaT =
WorK" would not be one of them.
I hope these brief notes help you to gain an understanding.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on tue 9 jan 07
Hi Gay,
Every pyrometer will give a different reading - to get cone 04 down I have
to set my controller to 1083C for instance.
Trust the cones and don't fire too fast - especially at the end of a firing
- to give the inside temperature a chance to even out. Soaking is good for
that but going at 50C for the last 100 C will always give more even
firings.
RR
>> If I am using the Orton cones and I get a cone 6 'touching' but my
>> highest
>> temperature was 2185 have I fired my glaze to cone 6? When I was
>> trying to
>> find the cause of my pinholing problems frequently I was told I was
>> underfiring because I programmed my kiln to go only to 2185 and not
>> higher.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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