Martinb888@AOL.COM on sun 17 dec 00
Had a very unnerving experience last night that I would like to avoid
repeating; I'm looking for confirmation that I have correctly figured out
what went wrong or other ideas. Over the years I have managed to blow up a
few things in the raku firing, either thick pieces that were still damp from
glazing (pop!), or greenware pieces that snuck in by mistake (pow!), however
last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
shelves, spewed hot shards several feet around the kiln and blew out the
burners! Luckly no one was hurt, but several of us were only about ten feet
from the kiln. Too close for comfort, do NOT want to do that again.
Thie kiln is fiber lined, two natural gas burners from underneath bounce off
a mullite/corderiete kiln shelf floor. Fired the same way as hundreds of
previous firings. Five or ten minutes on low, five or ten minutes on medium,
crank it up to high; a little faster or a little slower depending on what is
in there, but usually less than an hour total firing time to cone 07. The
first firing went great, nice results. As usual, I set pieces of cold kiln
shelf on the still hot floor to set the ware on for the second firing. About
five minutes after the first turn up, kaboom!
I am sure that it was not caused by gas; I was right there and both burners
were lit. It wasn't pots exploding; two of the six pieces in the kiln
survived intact and they were the thickest in the load. Besides, the violence
far surpassed any exploding pots I've ever seen. The only thing I can think
of that was unusual is that as I was putting in the shelf fragments I
noticed that one of the larger shelf pieces was silicon carbide instead of
the usual mullite. The silicon carbide shelf is so much denser I wonder if
the trapped moisture (they are stored outside) turned explosively to steam
before it could evaporate; together with the strength of the shelf I suppose
that could cause quite a violent result.
Anyone experienced this before? Or other possible explainations?
Thanks, Martin Butt
Coyote Clay and Color
Martinb888@aol.com
www.coyoteclay.com
(505)344-2250
Earl Brunner on sun 17 dec 00
I vote for the cold (wet?) kiln shelf blowing up. I say that based on
your description.
1. you are sure the burners didn't go out
2. pots when they blow usually don't go that violently
and even if they do, it's unlikely they would "shatter" the kiln shelving.
3. if a shelf did blow one would expect it to be in pieces
Was the silicon carbide shelf shattered?
Suggest pre drying them before use.
Martinb888@AOL.COM wrote:
> Had a very unnerving experience last night that I would like to avoid
> repeating; I'm looking for confirmation that I have correctly figured out
> what went wrong or other ideas. Over the years I have managed to blow up a
> few things in the raku firing, either thick pieces that were still damp from
> glazing (pop!), or greenware pieces that snuck in by mistake (pow!), however
> last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
> shelves, spewed hot shards several feet around the kiln and blew out the
> burners! Luckly no one was hurt, but several of us were only about ten feet
> from the kiln. Too close for comfort, do NOT want to do that again.
> Thie kiln is fiber lined, two natural gas burners from underneath bounce off
> a mullite/corderiete kiln shelf floor. Fired the same way as hundreds of
> previous firings. Five or ten minutes on low, five or ten minutes on medium,
> crank it up to high; a little faster or a little slower depending on what is
> in there, but usually less than an hour total firing time to cone 07. The
> first firing went great, nice results. As usual, I set pieces of cold kiln
> shelf on the still hot floor to set the ware on for the second firing. About
> five minutes after the first turn up, kaboom!
> I am sure that it was not caused by gas; I was right there and both burners
> were lit. It wasn't pots exploding; two of the six pieces in the kiln
> survived intact and they were the thickest in the load. Besides, the violence
> far surpassed any exploding pots I've ever seen. The only thing I can think
> of that was unusual is that as I was putting in the shelf fragments I
> noticed that one of the larger shelf pieces was silicon carbide instead of
> the usual mullite. The silicon carbide shelf is so much denser I wonder if
> the trapped moisture (they are stored outside) turned explosively to steam
> before it could evaporate; together with the strength of the shelf I suppose
> that could cause quite a violent result.
> Anyone experienced this before? Or other possible explainations?
> Thanks, Martin Butt
> Coyote Clay and Color
> Martinb888@aol.com
> www.coyoteclay.com
> (505)344-2250
>
> ______________________________________________________________________________
> 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.
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Marcia Selsor on sun 17 dec 00
WOW! That sounds dramatic. The experiences I have had with explosions in
raku are usually from heating too fast if the pots were not preheated.
We had a very fast wood fired raku kiln that we preheated pieces very
hot on top of the fire box. But once in a while one would blow. It would
blow 15-20 ft. out of the top of the fiber lined oil drum. This kiln was
a combo traditional shape Japanese kiln with a fire box and beehive
shaped chamber with a fiber lined oil drum on a hoist as the real firing
chamber. The fastest this kiln fired to temperature was 3.5 minutes but
that was towards the end of the day.
In the gas fired raku kiln I used for was a converted California kiln
with a home madee hinged door. We used silicon carbode shelves at first
but I think they held the heat too much for the next batch of pots.
Since we couldn't preheat as well in the kiln (no hot fire box to set
them on) I started using mullite shelves. This helped. I have gotten to
where I glaze the day before I fire.
Hope this helps. I know they can really blow!
Best wishes,
Marcia in Montana
Martinb888@AOL.COM wrote:
>
> Had a very unnerving experience last night that I would like to avoid
> repeating; I'm looking for confirmation that I have correctly figured out
> what went wrong or other ideas. Over the years I have managed to blow up a
> few things in the raku firing, either thick pieces that were still damp from
> glazing (pop!), or greenware pieces that snuck in by mistake (pow!), however
> last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
> shelves, spewed hot shards several feet around the kiln and blew out the
> burners! Luckly no one was hurt, but several of us were only about ten feet
> from the kiln. Too close for comfort, do NOT want to do that again.
> Thie kiln is fiber lined, two natural gas burners from underneath bounce off
> a mullite/corderiete kiln shelf floor. Fired the same way as hundreds of
> previous firings. Five or ten minutes on low, five or ten minutes on medium,
> crank it up to high; a little faster or a little slower depending on what is
> in there, but usually less than an hour total firing time to cone 07. The
> first firing went great, nice results. As usual, I set pieces of cold kiln
> shelf on the still hot floor to set the ware on for the second firing. About
> five minutes after the first turn up, kaboom!
> I am sure that it was not caused by gas; I was right there and both burners
> were lit. It wasn't pots exploding; two of the six pieces in the kiln
> survived intact and they were the thickest in the load. Besides, the violence
> far surpassed any exploding pots I've ever seen. The only thing I can think
> of that was unusual is that as I was putting in the shelf fragments I
> noticed that one of the larger shelf pieces was silicon carbide instead of
> the usual mullite. The silicon carbide shelf is so much denser I wonder if
> the trapped moisture (they are stored outside) turned explosively to steam
> before it could evaporate; together with the strength of the shelf I suppose
> that could cause quite a violent result.
> Anyone experienced this before? Or other possible explainations?
> Thanks, Martin Butt
> Coyote Clay and Color
> Martinb888@aol.com
> www.coyoteclay.com
> (505)344-2250
>
> ______________________________________________________________________________
> 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.
--
Marcia Selsor
selsor@imt.net
http://www.imt.net/~mjbmls
http://www.imt.net/~mjbmls/Tuscany2001.html
vince pitelka on sun 17 dec 00
> survived intact and they were the thickest in the load. Besides, the
violence
> far surpassed any exploding pots I've ever seen. The only thing I can
think
> of that was unusual is that as I was putting in the shelf fragments I
> noticed that one of the larger shelf pieces was silicon carbide instead of
> the usual mullite. The silicon carbide shelf is so much denser I wonder if
> the trapped moisture (they are stored outside) turned explosively to steam
> before it could evaporate; together with the strength of the shelf I
suppose
> that could cause quite a violent result.
Martin -
You have already figured it out. Do not store your kiln shelves outside any
more. There was another post recently from someone who had a kiln shelf
explode after it was stored outside. The most violent non-fuel-related
explosions in a kiln are from dense high-fired pieces with moisture
impacted. This has been discussed in regards to the freezing issue. A
piece of high-fired clay still absorbs a very small percentage of water, and
when the clay freezes the water cannot get out, and the piece disintegrates
over time. In this case, it disintegrates immediately, sometimes with
catastrophic force.
Believe me, it is not worth it taking any chances on this. But, you know
that now. Before you fire again, stack all your kiln shelves in your kiln
with spacers between, and heat them up slowly to drive off all the
moisture. Then keep them indoors when not in use.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@dekalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
http://www.craftcenter.tntech.edu/
Gabrielle on mon 18 dec 00
Hi Martin,
I'd have to say that you are probably right in your assumption
that the sil. carb. piece had absorbed moisture. That is the
usual reason that anything blows up in the kiln, only this time
the piece in question would have been very hard and when that
exploded it made quite a bang, whereas a clay piece in the kiln
that explodes isn't usually that heavy so the "pop" isn't that
dramatic. Sounds like you know exactly what's going on with your
firings, I'd trust your own judgements they seem very sound,
Gabrielle (surrounded by 10"s or more of wet, frozen, piles of snow
in Lotus Land :) Vancouver Island, BC
In clayart@egroups.com, Martinb888@A... wrote:
Had a very unnerving experience last night that I would like to avoid
repeating; I'm looking for confirmation that I have correctly figured
out
what went wrong or other ideas. Over the years I have managed to
blow up a
few things in the raku firing, either thick pieces that were still
damp from
glazing (pop!), or greenware pieces that snuck in by mistake (pow!),
however
last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
shelves, spewed hot shards several feet around the kiln and blew out
the
burners! Luckly no one was hurt, but several of us were only about
ten feet
from the kiln. Too close for comfort, do NOT want to do that again.
Thie kiln is fiber lined, two natural gas burners from underneath
bounce off
a mullite/corderiete kiln shelf floor. Fired the same way as hundreds
of
previous firings. Five or ten minutes on low, five or ten minutes on
medium,
crank it up to high; a little faster or a little slower depending on
what is
in there, but usually less than an hour total firing time to cone 07.
The
first firing went great, nice results. As usual, I set pieces of cold
kiln
shelf on the still hot floor to set the ware on for the second
firing. About
five minutes after the first turn up, kaboom!
I am sure that it was not caused by gas; I was right there and both
burners
were lit. It wasn't pots exploding; two of the six pieces in the kiln
survived intact and they were the thickest in the load. Besides, the
violence
far surpassed any exploding pots I've ever seen. The only thing I can
think
of that was unusual is that as I was putting in the shelf fragments I
noticed that one of the larger shelf pieces was silicon carbide
instead of
the usual mullite. The silicon carbide shelf is so much denser I
wonder if
the trapped moisture (they are stored outside) turned explosively to
steam
before it could evaporate; together with the strength of the shelf I
suppose
that could cause quite a violent result.
Anyone experienced this before? Or other possible explainations?
Thanks, Martin Butt
Coyote Clay and Color
Martinb888@a...
www.coyoteclay.com
(505)344-2250
______________________________________________________________________
________
Send postings to clayart@l...
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@p...
--- End forwarded message ---
Steve Mills on tue 19 dec 00
I think you've hit the nail on the head.
Steve
Bath
UK
In message , Martinb888@AOL.COM writes
>Had a very unnerving experience last night that I would like to avoid
>repeating; I'm looking for confirmation that I have correctly figured out
>what went wrong or other ideas. Over the years I have managed to blow up=
> a
>few things in the raku firing, either thick pieces that were still damp f=
>rom
>glazing (pop!), or greenware pieces that snuck in by mistake (pow!), howe=
>ver
>last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
>shelves, spewed hot shards several feet around the kiln and blew out the
>burners! Luckly no one was hurt, but several of us were only about ten fe=
>et
>=66rom the kiln. Too close for comfort, do NOT want to do that again.
>Thie kiln is fiber lined, two natural gas burners from underneath bounce =
>off
>a mullite/corderiete kiln shelf floor. Fired the same way as hundreds of
>previous firings. Five or ten minutes on low, five or ten minutes on medi=
>um,
>crank it up to high; a little faster or a little slower depending on what=
> is
>in there, but usually less than an hour total firing time to cone 07. The
>first firing went great, nice results. As usual, I set pieces of cold kil=
>n
>shelf on the still hot floor to set the ware on for the second firing. Ab=
>out
>five minutes after the first turn up, kaboom!
>I am sure that it was not caused by gas; I was right there and both burne=
>rs
>were lit. It wasn't pots exploding; two of the six pieces in the kiln
>survived intact and they were the thickest in the load. Besides, the viol=
>ence
>far surpassed any exploding pots I've ever seen. The only thing I can thi=
>nk
>of that was unusual is that as I was putting in the shelf fragments I
>noticed that one of the larger shelf pieces was silicon carbide instead o=
>f
>the usual mullite. The silicon carbide shelf is so much denser I wonder i=
>f
>the trapped moisture (they are stored outside) turned explosively to stea=
>m
>before it could evaporate; together with the strength of the shelf I supp=
>ose
>that could cause quite a violent result.
>Anyone experienced this before? Or other possible explainations?
>Thanks, Martin Butt
>Coyote Clay and Color
>Martinb888@aol.com
>www.coyoteclay.com
>(505)344-2250
--
Steve Mills
Bath
UK
Cantello Studios on fri 22 dec 00
I think you are in your thinking. If the shelf had a lot of moisture in them
they could blow.(?) have you ever tried to fire on pins of nicrome I made
some soft brick stilts . Using old soft brick and pushed nicrome wire bent
in the shape of a (V) in the brick. This keeps the pots off the hot flour
and. The neat thing about this is I can glaze the bottom of large plates and
just sponge off the foot. I started doing this when I saw wax burn off the
bottom of some large plates and crack them. My whole shelf is one big pin
cushion works for me good luck. Chris from Cantello Studios.
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Martinb888@AOL.COM
Sent: Sunday, December 17, 2000 12:19 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Explosion in raku kiln; Why?
Had a very unnerving experience last night that I would like to avoid
repeating; I'm looking for confirmation that I have correctly figured out
what went wrong or other ideas. Over the years I have managed to blow up a
few things in the raku firing, either thick pieces that were still damp from
glazing (pop!), or greenware pieces that snuck in by mistake (pow!), however
last nights noise was BOOM!!! Knocked the kiln lid off, shattered the
shelves, spewed hot shards several feet around the kiln and blew out the
burners! Luckly no one was hurt, but several of us were only about ten feet
from the kiln. Too close for comfort, do NOT want to do that again.
Thie kiln is fiber lined, two natural gas burners from underneath bounce off
a mullite/corderiete kiln shelf floor. Fired the same way as hundreds of
previous firings. Five or ten minutes on low, five or ten minutes on medium,
crank it up to high; a little faster or a little slower depending on what is
in there, but usually less than an hour total firing time to cone 07. The
first firing went great, nice results. As usual, I set pieces of cold kiln
shelf on the still hot floor to set the ware on for the second firing. About
five minutes after the first turn up, kaboom!
I am sure that it was not caused by gas; I was right there and both burners
were lit. It wasn't pots exploding; two of the six pieces in the kiln
survived intact and they were the thickest in the load. Besides, the
violence
far surpassed any exploding pots I've ever seen. The only thing I can think
of that was unusual is that as I was putting in the shelf fragments I
noticed that one of the larger shelf pieces was silicon carbide instead of
the usual mullite. The silicon carbide shelf is so much denser I wonder if
the trapped moisture (they are stored outside) turned explosively to steam
before it could evaporate; together with the strength of the shelf I suppose
that could cause quite a violent result.
Anyone experienced this before? Or other possible explainations?
Thanks, Martin Butt
Coyote Clay and Color
Martinb888@aol.com
www.coyoteclay.com
(505)344-2250
____________________________________________________________________________
__
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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