ranmcc@MSN.COM on sat 19 sep 09
Is there an optimum temperature to to achieve burn out of organic materials
and if so how long should I hold at that temperature. Is it better to get
to that temperature and hold or is a long firing schedule better?
Randy
Miriam Schiller on sat 19 sep 09
Randy=3D2C
=3D20
I read in a few books that all organic materials burn out by about 1000 Fah=
=3D
renheit=3D2C and that making sure the kiln is vented at least until then wi=
ll=3D
let them all go out. So any temperature over 1000 is "optimum" and will g=
=3D
et out all organics=3D2C just make sure you're venting your kiln.
=3D20
In terms of firing=3D2C slower isn't always necessary=3D2C but I think it d=
epen=3D
ds on what you are firing. I have read in my kiln manual that large=3D2C h=
ea=3D
vy walled=3D2C or slightly damp pieces should be fired more slowly=3D2C whe=
reas=3D
if you are firing a kiln load of small 1/2 pound bone dry mugs=3D2C really=
s=3D
low probably isn't necessary. But regardless of your firing speed=3D2C as =
lo=3D
ng as your final temperature is over 1000F=3D2C the organic matter will be =
go=3D
ne. And an end hold is always good because it helps distribute the heat ev=
=3D
enly throughout the kiln.
=3D20
Regards=3D2C
Miriam Schiller
www.potterybymiriam.etsy.com
www.potterybymiriam.wordpress.com
=3D20
> Date: Sat=3D2C 19 Sep 2009 09:54:33 -0400
> From: ranmcc@MSN.COM
> Subject: Eliminating clay as a source of pinholes?
> To: Clayart@LSV.CERAMICS.ORG
>=3D20
> Is there an optimum temperature to to achieve burn out of organic materia=
=3D
ls
> and if so how long should I hold at that temperature. Is it better to get
> to that temperature and hold or is a long firing schedule better?
>=3D20
>=3D20
> Randy =3D0A=3D
_________________________________________________________________=3D0A=3D
Microsoft brings you a new way to search the web. Try Bing=3D99 now=3D0A=
=3D
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ore_ta=3D
gline_try bing_1x1=3D
Michael Wendt on sun 20 sep 09
Randy,
A minor note on Miriam's post...
she wrote:
"In terms of firing, slower isn't always necessary, but I
think it depends on what you are firing. I have read in my
kiln manual that large, heavy walled, or slightly damp
pieces should be fired more slowly, whereas if you are
firing a kiln load of small 1/2 pound bone dry mugs, really
slow probably isn't necessary. But regardless of your
firing speed, as long as your final temperature is over
1000F, the organic matter will be gone. And an end hold is
always good because it helps distribute the heat evenly
throughout the kiln.
Regards,
Miriam Schiller"
Metakaolin forms at about 1150 F. Firing bisque below that
temperature is unwise because the clay can still start to
rewet if fired below the metakaolin forming temperature.
Thus, even if the carbon was gone, the piece is not bisqued.
I started insulating fire brick making trials in the early
70s using fine sawdust as the burnout medium. To my
surprise, sawdust bricks fired to cone ten still had black
cores sometimes (the black is unreacted carbon).
As I made more bricks and watched how and where they were
fired it became clear that air circulation plays a vital
role in purging carbonaceous matter from clay. I had to pit
spacers under and between the blanks to eliminate the
problem.
Common bisque practice is to stack pieces one inside another
and to box (stack lip to lip) pots. If you have intermittent
problems with blistering, this could be a possible cause.
Allow for air circulation, fire hotter bisque... I fire cone
09-08 range. Don't overload and take your time.
Firing speed and especially firming speed during glaze
firing plays a key role in finished quality. I used to fire
the kiln like a rocket. My motto was " in by 10:00 over by
5:00"
That pace meant the final cones dropped at a rate of 20
minutes per cone just like a clock. Blisters happened.
Now I allow a much slower top end. rate of 40-50 minutes
per cone and the glaze finishes are brighter, smoother and
the desired variegation where glazes are layered is
stunning.
Losing even one or two pots per load will cost you more than
the electricity or fuel required to fire slower.
One final note:
Chemical reactions happen faster at higher temperatures so
firing slower near the end will have the greatest benefit.
Regards,
Michael Wendt
Ron Roy on thu 24 sep 09
At 400F (204C) the organics are still there - they ignite about 700C upward=
=3D
s
- 1000C should do it for some clays but others need a high temp because of
the amount of organics and/or thickness of ware. The other important factor
is the amount of oxygen - if it's not there the organics stay as carbon
(think charcoal) and can help overfire clay if iron is present.
When pots are stacked rim to rim for instance - after the trapped oxygen is
used up burning the organics - you can them have a reducing atmosphere.
Sometimes this will happen inside a foot rim and the clay can bloat in that
area simply because there was not enough oxygen to burn everything.
It's very hard to predict which clays have the carbon content - sometimes
the same clay will have lots and sometimes less - if you are firing dark
clays (iron bearing) best to make sure you have plenty of fresh air around
from 700C (1300F) to the end of a bisque.
RR
On Sat, Sep 19, 2009 at 7:34 PM, Miriam Schiller wr=
=3D
ote:
> Randy,
>
>
>
> I read in a few books that all organic materials burn out by about 1000
> Fahrenheit, and that making sure the kiln is vented at least until then w=
=3D
ill
> let them all go out. So any temperature over 1000 is "optimum" and will =
=3D
get
> out all organics, just make sure you're venting your kiln.
>
>
>
> In terms of firing, slower isn't always necessary, but I think it depends
> on what you are firing. I have read in my kiln manual that large, heavy
> walled, or slightly damp pieces should be fired more slowly, whereas if y=
=3D
ou
> are firing a kiln load of small 1/2 pound bone dry mugs, really slow
> probably isn't necessary. But regardless of your firing speed, as long a=
=3D
s
> your final temperature is over 1000F, the organic matter will be gone. A=
=3D
nd
> an end hold is always good because it helps distribute the heat evenly
> throughout the kiln.
>
>
>
> Regards,
>
> Miriam Schiller
>
> www.potterybymiriam.etsy.com
>
> www.potterybymiriam.wordpress.com
>
> > Date: Sat, 19 Sep 2009 09:54:33 -0400
> > From: ranmcc@MSN.COM
> > Subject: Eliminating clay as a source of pinholes?
> > To: Clayart@LSV.CERAMICS.ORG
> >
> > Is there an optimum temperature to to achieve burn out of organic
> materials
> > and if so how long should I hold at that temperature. Is it better to g=
=3D
et
> > to that temperature and hold or is a long firing schedule better?
> >
> >
> > Randy
> _________________________________________________________________
> Microsoft brings you a new way to search the web. Try Bing=3D99 now
>
> http://www.bing.com?form=3D3DMFEHPG&publ=3D3DWLHMTAG&crea=3D3DTEXT_MFEHPG=
_Core_=3D
tagline_trybing_1x1
--=3D20
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
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