vince pitelka on thu 15 nov 01
> Students in my Ceramics class tried a reduction firing in an inverted
trash
> can set into a bed of sawdust. We got the instructions out of Ceramics
> Monthly - November 1999 pages 59-66. The unfired, burnished greenware
> exploded (three separate incidents). What are we doing wrong?
Christine -
If you are bothering to heat the wares in an electric kiln, why not go ahead
and bisque-fire them and avoid any chance of having them blow up in the
sawdust. Also, a sawdust "firing" is not a true firing process, and does
not reach even minimum sintering temperature, so you need to bisque-fire
them if you want permanent wares. Wares fired the way you describe would
probably slake down in water.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Megan Ratchford on thu 15 nov 01
Christine,
I fire burnished greenware pots without any pre-bisquing, although it
couldn't hurt! I do let my pots dry a week open after burnishing, but it
all depends on how much humidity you have in the atmosphere.
I have a metal trashcan that I have drilled holes from the top to bottom
at about three inches apart from each other. I place the pots inside the
can on about 6 inches of sawdust than fill to 6 inches above. I place
wadded up balls of newspaper on top and light. When the paper is all burned
away the remaining sawdust should be black with faint whisps of smoke coming
from the top. Too much smoke and the sawdust burns to quickly and cracks
the pots, too little and the sawdust won't burn evenly. This must be done
on a very still day to prevent the windward side of the can from moving too
fast and causing unevenness in the firing. Use the can lid as a sort of
damper. I leave it cracked while getting the smolder going and then lay it
on without pressing down for the remainder of the firing. Also, you may
need to relight the top. This firing goes for about 15 hours. The goal is
for the sawdust to burn like a cigarette. If it's slow enough the pots are
very black and lovely and whole.
I haven't seen the instructions you followed but I wouldn't want to
smoke any pot so fast. (At least the firing seems fast from your
discription! grin)
Megan
Belton, Christine on thu 15 nov 01
Hi folks,
Students in my Ceramics class tried a reduction firing in an inverted trash
can set into a bed of sawdust. We got the instructions out of Ceramics
Monthly - November 1999 pages 59-66. The unfired, burnished greenware
exploded (three separate incidents). What are we doing wrong?
Here are our steps:
* We begin with burnished greenware
* Heat greenware in electric kiln (3 hours on low)
* Wrap hot greenware in fabric to keep warm
* Take outside and put greenware on raised kiln shelves that are
nestled in a 6" bed of sawdust
* Invert a metal trashcan over the greenware and use the sawdust to
"seal" the edges
* Place pieces of wood and twists of newspaper around the trashcan
* Light the fire
* Stand back and wait for the fire to burn down
The greenware has been exploding about 5 minutes into the firing.
All of the shattered pieces look great - black and shiny!......but shattered
nonetheless.
What are we doing wrong? Do we need the greenware to be a certain
temperature? I know it's thoroughly dry because not only did it sit for a
couple of weeks, but we soaked it in the electric kiln for hours. The ground
is bone dry.....we are in pre-drought conditions.
Help!
Thanks-
Christine
also at: sculpturegrl@aol.com
Rick Brady on thu 15 nov 01
Christine,
Try bisque firing to 011/012 first. That will give you stronger pots and preserve the burnishing. You may still see some cracks from thermal shock but I doubt any pieces will explode. Your greenware is probably still holding some moisture which is causing the problem. Good Luck.
Rick Brady
Pleasanton, CA
-----Original Message-----
From: Belton, Christine [mailto:BELTOCHR@SSD.K12.PA.US]
Sent: Thursday, November 15, 2001 10:41 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Reduction firing question........explosions
Hi folks,
Students in my Ceramics class tried a reduction firing in an inverted trash
can set into a bed of sawdust. We got the instructions out of Ceramics
Monthly - November 1999 pages 59-66. The unfired, burnished greenware
exploded (three separate incidents). What are we doing wrong?
Here are our steps:
* We begin with burnished greenware
* Heat greenware in electric kiln (3 hours on low)
* Wrap hot greenware in fabric to keep warm
* Take outside and put greenware on raised kiln shelves that are
nestled in a 6" bed of sawdust
* Invert a metal trashcan over the greenware and use the sawdust to
"seal" the edges
* Place pieces of wood and twists of newspaper around the trashcan
* Light the fire
* Stand back and wait for the fire to burn down
The greenware has been exploding about 5 minutes into the firing.
All of the shattered pieces look great - black and shiny!......but shattered
nonetheless.
What are we doing wrong? Do we need the greenware to be a certain
temperature? I know it's thoroughly dry because not only did it sit for a
couple of weeks, but we soaked it in the electric kiln for hours. The ground
is bone dry.....we are in pre-drought conditions.
Help!
Thanks-
Christine
also at: sculpturegrl@aol.com
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iandol on fri 16 nov 01
Dear Christine.
I have had a quick look at that article and it says nothing about the =
type of clay being used. However, I would suspect that it is heavily =
tempered.
In terms of standard firing practice this process ignores the basic =
chemistry of clay as it is being heated. No allowance is made to for =
water vapour which is generated during the chemical decomposition of =
clay to escape slowly from the fabric of the pot. Although this =
reaction is expected to be complete by the time the temperature gets to =
600 Celsius it can lag and 800 Celsius gives a a better margin, (though =
that is above the recommended cone for the process). Which is why slow =
bisque firing is generally a recommended procedure
Such rapid heating, as is described in that article, might be so =
excessive as to not allow sufficient time for the superheated steam =
created by decomposition to diffuse from the interior of the clay. My =
expectation would be that such firings will have a catastrophic effect =
on most clays. Hence, my opinion that the clay being used has a large =
proportion of coarse temper in its constitution.
I hope these notes give you a lead as to the cause and solution of your =
problem.
Best regards,
Ivor Lewis. Redhill, South Australia
Belton, Christine on fri 16 nov 01
Thanks Rick,
I'll bisque them first at 012 next time. Christine
> -----Original Message-----
> From: Rick Brady [SMTP:RickB@NETRO-CORP.COM]
> Sent: Thursday, November 15, 2001 5:16 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Reduction firing question........explosions
>
> Christine,
>
> Try bisque firing to 011/012 first. That will give you stronger pots and
> preserve the burnishing. You may still see some cracks from thermal shock
> but I doubt any pieces will explode. Your greenware is probably still
> holding some moisture which is causing the problem. Good Luck.
>
> Rick Brady
> Pleasanton, CA
>
> -----Original Message-----
> From: Belton, Christine [mailto:BELTOCHR@SSD.K12.PA.US]
> Sent: Thursday, November 15, 2001 10:41 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Reduction firing question........explosions
>
>
> Hi folks,
>
> Students in my Ceramics class tried a reduction firing in an inverted
> trash
> can set into a bed of sawdust. We got the instructions out of Ceramics
> Monthly - November 1999 pages 59-66. The unfired, burnished greenware
> exploded (three separate incidents). What are we doing wrong?
>
> Here are our steps:
>
> * We begin with burnished greenware
> * Heat greenware in electric kiln (3 hours on low)
> * Wrap hot greenware in fabric to keep warm
> * Take outside and put greenware on raised kiln shelves that are
> nestled in a 6" bed of sawdust
> * Invert a metal trashcan over the greenware and use the sawdust to
> "seal" the edges
> * Place pieces of wood and twists of newspaper around the trashcan
> * Light the fire
> * Stand back and wait for the fire to burn down
>
> The greenware has been exploding about 5 minutes into the firing.
> All of the shattered pieces look great - black and shiny!......but
> shattered
> nonetheless.
>
> What are we doing wrong? Do we need the greenware to be a certain
> temperature? I know it's thoroughly dry because not only did it sit for a
> couple of weeks, but we soaked it in the electric kiln for hours. The
> ground
> is bone dry.....we are in pre-drought conditions.
>
> Help!
>
> Thanks-
>
> Christine
> also at: sculpturegrl@aol.com
>
> __________________________________________________________________________
> ____
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
> __________________________________________________________________________
> ____
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
Roger Korn on fri 16 nov 01
I'm not sure that you can bisque that high for burnished ware. My wife works in the Pueblo style and we find that you lose some burnish anywhere above ^020. Probably depends on the clays used in the body and terra sig.
Roger Korn
McKay Creek Ceramics
In AZ: 928-567-5699 <-
In OR: 503-647-5464
Rick Brady wrote:
> Christine,
>
> Try bisque firing to 011/012 first. That will give you stronger pots and preserve the burnishing. You may still see some cracks from thermal shock but I doubt any pieces will explode. Your greenware is probably still holding some moisture which is causing the problem. Good Luck.
>
> Rick Brady
> Pleasanton, CA
>
> -----Original Message-----
> From: Belton, Christine [mailto:BELTOCHR@SSD.K12.PA.US]
> Sent: Thursday, November 15, 2001 10:41 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Reduction firing question........explosions
>
> Hi folks,
>
> Students in my Ceramics class tried a reduction firing in an inverted trash
> can set into a bed of sawdust. We got the instructions out of Ceramics
> Monthly - November 1999 pages 59-66. The unfired, burnished greenware
> exploded (three separate incidents). What are we doing wrong?
>
> Here are our steps:
>
> * We begin with burnished greenware
> * Heat greenware in electric kiln (3 hours on low)
> * Wrap hot greenware in fabric to keep warm
> * Take outside and put greenware on raised kiln shelves that are
> nestled in a 6" bed of sawdust
> * Invert a metal trashcan over the greenware and use the sawdust to
> "seal" the edges
> * Place pieces of wood and twists of newspaper around the trashcan
> * Light the fire
> * Stand back and wait for the fire to burn down
>
> The greenware has been exploding about 5 minutes into the firing.
> All of the shattered pieces look great - black and shiny!......but shattered
> nonetheless.
>
> What are we doing wrong? Do we need the greenware to be a certain
> temperature? I know it's thoroughly dry because not only did it sit for a
> couple of weeks, but we soaked it in the electric kiln for hours. The ground
> is bone dry.....we are in pre-drought conditions.
>
> Help!
>
> Thanks-
>
> Christine
> also at: sculpturegrl@aol.com
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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