Lee Love on mon 27 sep 10
Some more info:
" Crash cooling not only prevents the crystobolite build up and
dunting associated with this, but also has a positive effect on the
colour development. This is my firing cycle however others might
vary."
Ceramic Course: soda firing's Blog
International School of Ceramic Art in Tuscany
http://internationalschoolofceramicart.wordpress.com/
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Lee Love on mon 27 sep 10
On Mon, Sep 27, 2010 at 6:00 PM, Frances Howard
wrote:
> We fire with an electric kiln with computer controller and the lid has ne=
=3D
ver been opened >until the kiln is stone cold. =3DA0I haven't got the firin=
g =3D
schedule here but could get it, likewise I >can supply the glaze recipes, w=
=3D
ell everyone knows spearmint.
Slow cooling in a high silica body can cause this. I've shared
before Mick Casson's crash cooling to 1100*C to prevent this in a high
silica clay. Holding a kiln to create crystals in glazes also causes
crystals in high silica clay bodies.
So, ironically, opening the lid at the end of cooling might help
prevent it.
--=3D20
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Frances Howard on mon 27 sep 10
The recent discussions on crystobalite, quartz inversions, dunting and crac=
king has been very interesting to our group and we wonder if it might be ap=
plicable to us. We haven't had this problem before but now here it is.
Several pieces have been cracking during the cooling stage , a jug split f=
rom the rim and the crack circled the base, another jug, (made by another p=
erson) split in the main bulge on the body and so on. Mostly we are using =
Tucker's mid smooth stone but there is B mix involved too. The glazes last=
week which dunted were spearmint, chun white, and Pete Pinnell's black gre=
en, all of which we have used dozens of times before perfectly. And the pi=
eces were thrown by experienced potters and were well made. These were l=
ast weeks casualties and previous weeks have had more. So we are at a loss=
to know quite what might be going on.
We fire with an electric kiln with computer controller and the lid has neve=
r been opened until the kiln is stone cold. I haven't got the firing sched=
ule here but could get it, likewise I can supply the glaze recipes, well ev=
eryone knows spearmint.
If anyone has any ideas about what we might be doing wrong or what we shoul=
d be changing we'd be most grateful . As far as we know the bisque ware was=
n't damaged but that's always possible I suppose in a group situation.
Many thanks Frances Howard
Frances Howard on tue 28 sep 10
That's one of our unknowns. I don't think the peepholes were opened, but
the person doing the unloading didn't make a note of where the cracked pots
were in the kiln. She has been doing so since last week. Frances
--------------------------------------------------
From: "Marcia Selsor"
Sent: Tuesday, September 28, 2010 7:59 AM
To: "Frances Howard"
Cc:
Subject: Re: dunting pots
> Has anyone opened the peep holes? You can get a cold draft through them a=
s
> well as opening the lid.
> Were the casualties close together or elsewhere in the kiln?
> Marcia
> On Sep 27, 2010, at 6:00 PM, Frances Howard wrote:
>
>> The recent discussions on crystobalite, quartz inversions, dunting and
>> cracking has been very interesting to our group and we wonder if it migh=
t
>> be applicable to us. We haven't had this problem before but now here i=
t
>> is.
>>
>> Several pieces have been cracking during the cooling stage , a jug split
>> from the rim and the crack circled the base, another jug, (made by
>> another person) split in the main bulge on the body and so on. Mostly w=
e
>> are using Tucker's mid smooth stone but there is B mix involved too. Th=
e
>> glazes last week which dunted were spearmint, chun white, and Pete
>> Pinnell's black green, all of which we have used dozens of times before
>> perfectly. And the pieces were thrown by experienced potters and were
>> well made. These were last weeks casualties and previous weeks have
>> had more. So we are at a loss to know quite what might be going on.
>>
>> We fire with an electric kiln with computer controller and the lid has
>> never been opened until the kiln is stone cold. I haven't got the firin=
g
>> schedule here but could get it, likewise I can supply the glaze recipes,
>> well everyone knows spearmint.
>>
>> If anyone has any ideas about what we might be doing wrong or what we
>> should be changing we'd be most grateful . As far as we know the bisque
>> ware wasn't damaged but that's always possible I suppose in a group
>> situation.
>> Many thanks Frances Howard
>>
>
> Marcia Selsor
> http://www.marciaselsor.com
>
>
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.856 / Virus Database: 271.1.1/3164 - Release Date: 09/28/10
> 03:34:00
>
Marcia Selsor on tue 28 sep 10
Has anyone opened the peep holes? You can get a cold draft through them =3D
as well as opening the lid.
Were the casualties close together or elsewhere in the kiln?
Marcia
On Sep 27, 2010, at 6:00 PM, Frances Howard wrote:
> The recent discussions on crystobalite, quartz inversions, dunting and =
=3D
cracking has been very interesting to our group and we wonder if it =3D
might be applicable to us. We haven't had this problem before but now =3D
here it is.
>=3D20
> Several pieces have been cracking during the cooling stage , a jug =3D
split from the rim and the crack circled the base, another jug, (made by =
=3D
another person) split in the main bulge on the body and so on. Mostly =3D
we are using Tucker's mid smooth stone but there is B mix involved too. =
=3D
The glazes last week which dunted were spearmint, chun white, and Pete =3D
Pinnell's black green, all of which we have used dozens of times before =3D
perfectly. And the pieces were thrown by experienced potters and were =3D
well made. These were last weeks casualties and previous weeks have =3D
had more. So we are at a loss to know quite what might be going on.
>=3D20
> We fire with an electric kiln with computer controller and the lid has =
=3D
never been opened until the kiln is stone cold. I haven't got the =3D
firing schedule here but could get it, likewise I can supply the glaze =3D
recipes, well everyone knows spearmint.
>=3D20
> If anyone has any ideas about what we might be doing wrong or what we =3D
should be changing we'd be most grateful . As far as we know the bisque =3D
ware wasn't damaged but that's always possible I suppose in a group =3D
situation.
> Many thanks Frances Howard
>=3D20
Marcia Selsor
http://www.marciaselsor.com
Lee Love on tue 28 sep 10
On Mon, Sep 27, 2010 at 6:00 PM, Frances Howard
wrote:
> We fire with an electric kiln with computer controller and the lid has ne=
=3D
ver been opened >until the kiln is stone cold. =3DA0I haven't got the firin=
g =3D
schedule here but could get it, likewise I >can supply the glaze recipes, w=
=3D
ell everyone knows spearmint.
A schedule might give a clue. Did you cool and hold?
--=3D20
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Steve Slatin on wed 29 sep 10
Yes -- I used to have a mug with a perfect round crack in
the side where it was facing the peep. I now only pull the
plugs at a lower temperature. Live and learn ...
Steve Slatin --
N48.0886450
W123.1420482
--- On Tue, 9/28/10, Marcia Selsor wrote:
> Has anyone opened the peep holes? You
> can get a cold draft through them as well as opening the
> lid.
> Were the casualties close together or elsewhere in the
> kiln?
> Marcia
Dinah Snipes Steveni on wed 29 sep 10
Sorry about the problems. Just a thought and without knowing workshop pract=
ices and so forth: are the folks drying their pieces in a drafty place unpr=
otected, or placing pieces on a cooling down kiln to hasten drying times? P=
roblems aren't found out until pieces go through the heat work. I'm sure th=
ere will be more observations and solutions. I speak from bitter experience=
on both those stupid practices!
Dinah
http://www.dinahsnipessteveni.com
Facebook: Dianthus Visual Arts
http://www.washingtonpotters.org/WPA_Gallery.htm
jd.steveni@comcast.com
360.336.6624
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