Larry Kruzan on mon 18 oct 10
Hi Alice,
I'm so sorry to hear about your loss. What an incredible explosion that mus=
t
have been.
When you re-glazed the piece that you think caused the explosion, did you
dip the piece or spray the glaze on the piece?
My thinking is that if you dipped it, water became trapped in a pocket.
Since the clay was vitrified from the first firing, the steam generated may
not have been able to fully escape until the pot blew apart. You would thin=
k
that if water could get in, steam could get out - but what you have sure
sounds like a steam explosion.
I don't know if this is what happened or not but it is a possibility.
About this kiln - Are you saying that you had full round shelves mixed with
half shelves??? That's not good practice. Were any of the shelves or posts
broken? I'd doubt that shelves breaking would cause the amount of damage yo=
u
have.
Sorry, but I also doubt that your elements will have much life after being
shorted with glaze covered shards. I don't have a clue how you might clean
them in order to save them. Not sure there is a way. Be sure to get all the
glaze cleaned up that you can find - melting glaze will eat through kiln
bricks if ignored.
Wish I could help more. I've had a glazed piece blow up in my gas kiln -
that was bad enough, I can't imagine how hard cleaning up a electric kiln
will be.
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
<<<<<< SNIP >>>>>>>>>
I had one full
shelf (as opposed to half shelves) that was 2 shelves below the explosion
and I
thought the pieces under it would be safe. Wrong. Every piece had shards
in
it. That's why I think there must have been a cyclone: how else could the
shards
have gotten under a solid shelf?
<<<<<<<<<< SNIP >>>>>>>>>>>>>>
Time to pop a cold one.
Alice DeLisle
=3D=3D=3D=3D=3D=3D=3D
Email scanned by PC Tools - No viruses or spyware found.
(Email Guard: 7.0.0.18, Virus/Spyware Database: 6.16100)
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Alice DeLisle on mon 18 oct 10
I just had the ultimate kiln explosion. I am sure that it was followed by =
a
major cyclone because that is the only way that I can explain it.
Top loading electric kiln, cone 6 oxidation firing, fired normally (electro=
nic
controller, witness cones). Thermocouple read less than 170oF when I opene=
d
it. There was a re-fired piece that exploded into 10's of thousands of sha=
rds
that went everywhere. Every other piece in the kiln, all the shelves, the
walls, the elements, the bottom with element, all were covered in small to
medium size shards. One piece even had shards underneath it. I had one fu=
ll
shelf (as opposed to half shelves) that was 2 shelves below the explosion a=
nd I
thought the pieces under it would be safe. Wrong. Every piece had shards =
in
it. That's why I think there must have been a cyclone: how else could the s=
hards
have gotten under a solid shelf?
The piece that exploded was a vase built from 4 slabs, about 8 in tall. It=
had
been fired once but I was not happy with the glaze, so I re-glazed it and f=
ired
it again. (Next time, I will just throw it away!!) The bottom was one slab=
and
the walls were composed of 2 slabs with a small belt over them that was the
4th. Somewhere in that belt region is where the explosion took place. The
bottom was still attached to part of one slab and a small ring was sitting =
next
to it that was part of the top slab. But it was like the skin came off the
rest. There were thin small sheets with glaze on one side that would have =
been
on the surfaces, inside and out, in addition to the 10's of thousands of sh=
ards
of unglazed internal pieces.
My biggest concern is the kiln elements. There are some shards on the elem=
ents
with glaze on them. Any advice on how best to remove them?
Time to pop a cold one.
Alice DeLisle
wanderland@att.net
http://www.etsy.com/shop/IslandTextures
William & Susan Schran User on tue 19 oct 10
On 10/18/10 6:46 PM, "Alice DeLisle" wrote:
> There were thin small sheets with glaze on one side that would have been
> on the surfaces, inside and out, in addition to the 10's of thousands of
> shards
> of unglazed internal pieces.
> My biggest concern is the kiln elements. There are some shards on the
> elements
> with glaze on them. Any advice on how best to remove them?
Alice,
There was no cyclone in the kiln, but rather, the action of water changing
to steam and as you've discovered, a very powerful event.
I suspect, in re-glazing your piece, you had gotten water into the clay tha=
t
had not had sufficient time to completely dry. If you do this again,
re-glaze then heat pot in your oven to just about 200F for a couple hours.
Regards the elements, remove everything from the kiln (shelves) and using
vacuum with hose, shine a flashlight along each element and carefully vacuu=
m
out all debris. May want to also have a needle tool and needle nose pliers
in case a small piece is stuck behind the element. Be careful not to move
the element as they are very brittle.
If you have small glazed bits fused to the element, then you'll need a smal=
l
propane torch to heat the element to red hot before you pick the bit off
with needle nose pliers. Any bits left on may eventually short out the
element causing failure.
Have had this happen at school in bisque firings when pots still a bit wet
get loaded in the kiln. A real pain to clean out sometimes.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Arnold Howard on tue 19 oct 10
From: "Alice DeLisle"
> My biggest concern is the kiln elements. There are some
> shards on the elements
> with glaze on them. Any advice on how best to remove
> them?
-----------
Alice, have you figured out what caused the explosion?
First, thoroughly vacuum the firing chamber. (Do not touch
the thermocouple with the vacuum nozzle.) Remove shards from
the firebrick walls, bottom and lid. Vacuum the element
grooves.
Then examine the grooves for traces of clay fragments. Use a
dental mirror and flash light if necessary. Shards that have
stuck to an element can be removed with a screwdriver.
In spite of your best efforts, though, an element or two may
fail.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
Vince Pitelka on tue 19 oct 10
Alice DeLisle wrote:
"The piece that exploded was a vase built from 4 slabs, about 8 in tall. I=
t
had been fired once but I was not happy with the glaze, so I re-glazed it
and fired it again. (Next time, I will just throw it away!!) The bottom wa=
s
one slab and the walls were composed of 2 slabs with a small belt over them
that was the 4th. Somewhere in that belt region is where the explosion too=
k
place. The bottom was still attached to part of one slab and a small ring
was sitting next to it that was part of the top slab. But it was like the
skin came off the rest. There were thin small sheets with glaze on one sid=
e
that would have been on the surfaces, inside and out, in addition to the
10's of thousands of shards of unglazed internal pieces. My biggest concern
is the kiln elements. There are some shards on the elements with glaze on
them. Any advice on how best to remove them?"
Hi Alice -
First, I am very sorry that this happened to your kiln. I really admire
your ability to describe it so clinically, and then to go "pop a cold one."
That is a lot more productive than despair, although I expect you felt some
of that too. Regarding repairing the kiln, Arnold Howard's post gives soun=
d
advice on what to do, and a warning that you might lose some elements.
Glaze is highly acidic when it melts, so if any glaze has pooled on the
elements, there is no way to remove it, and it will eventually burn through
the element. That can happen in a single firing with a single glaze contac=
t
against the elements. That is the unfortunate truth.
Once you remove all the shards and glaze contamination from the surface of
the refractory and the element grooves, the kiln should be fine. If you
determine that there are a lot of shards stuck within the element grooves
that you cannot access because of the elements, and if you determine that
there are spots of glaze on the elements, then you may decide to just scrap
the elements and start afresh. That would be a shame, but only you can mak=
e
the determination as to whether it is the best course of action.
When you say you were not happy with the glaze, how long had the piece been
sitting around after the initial glaze firing? Is there any chance that it
had water in it for any period of time? Was it sitting in an especially
damp or humid environment for a prolonged period? I have never heard of
such an explosion occurring just from water absorbed during glazing. Peopl=
e
re-glaze and re-fire things all the time.
Vitrified glaze ware has the capacity to explode very violently and even
catastrophically if it truly has water impacted within it. The reason this
can happen is the same reason why vitrified ware does not hold up well
outdoors in a freezing climate. The porosity of vitrified clay should be
very low, but if there is any porosity at all, the clay can absorb water
over time, and when that happens, the water cannot escape easily, in either
heating above boiling, or cooling below freezing. It builds up pressure, an=
d
if the heating or cooling is extreme enough, the piece breaks.
What happens in the case of freezing is just simple breakage, and however
much we might bemoan the loss of the piece, it is of minor significance as
compared to what happens when such a piece is heated and the impacted water
turns to steam. It will build up more and more pressure until it exceeds
the mechanical strength of the clay, and then ka-blam. I saw this happen i=
n
spectacular fashion to a large stoneware pitcher that had been sitting atop
the firebox of our Bourry-box wood kiln. It was there when I arrived at th=
e
Craft Center in 1994. There is a minimal roof above that kiln, and the
pitcher had apparently gathered water. During a firing about ten or twelve
years ago, we had just gotten the first chamber to temperature and had move=
d
around to the side of the kiln to fire the second chamber when the pitcher
exploded like a small artillery shell. Chunks of that pitcher hit the wall=
s
of the building like bullets, and there was an incredible racket as they
landed all up and down the shed that runs along the back of the building.
Several windows were broken. If any of us had been in the line of fire, it
could have been fatal. I really learned respect for the power of expanding
steam from water impacted in a "vitrified" piece of clay. A vitrified clay
piece that has been in regular contact with water should never be refired.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Snail Scott on tue 19 oct 10
On Oct 18, 2010, at 5:46 PM, Alice DeLisle wrote:
> I just had the ultimate kiln explosion...
Re-glazing can be hazardous this way, since
any moisture that finds its way into even the
minimal porosity of most vitrified clays will have
a very hard time escaping, like moisture in a
cracked sealed-beam headlight.
I think that the reason you had such widespread
shard distribution is ricochet, pure and simple.
When vitrified clay does blow up (on those rare
occasions when it does) the force is HUGE
compared to a greenware explosion.
For cleaning the element channels, a crevice
nozzle on a shop-vac or handheld vacuum will
be the best. Give the elements a very gentle
wiggle _after_ the first vacuum attempt on each
section, while you vacuum it again.
-Snail
Snail Scott on tue 19 oct 10
On Oct 19, 2010, at 4:45 PM, Vince Pitelka wrote:
> ...I have never heard of
> such an explosion occurring just from water absorbed during
> glazing. People
> re-glaze and re-fire things all the time...
It is very rare, but I have encountered three
incidences of this phenomenon in the past.
Two involved high-bisqued clay with nearly
complete coverage from a commercial low-
fire-rated underglaze. The underglaze was
apparently sufficiently vitrified that it prevented
the escape of the glaze moisture, which had
presumably penetrated through the 'dry' foot
and the deeper (un-underglazed) convolutions
of the form. The lower portions of the work
blew to smithereens during the early phases
of the glaze firing, though the upper sections
remained largely intact.
The third incident was an example of a re-glazed
piece, and the clay body, though given to students
as a nominal ^6 body, was not really vitrified even
at ^8. So, glaze moisture could be easily absorbed
through the dry foot, but had difficulty escaping
again through the existing vitreous glaze layer.
As might be expected, the evident force of the
explosion of the high-fired piece was very
much greater than that of the bisque-fired pieces.
-Snail
>
>
> Vitrified glaze ware has the capacity to explode very violently and
> even
> catastrophically if it truly has water impacted within it. The
> reason this
> can happen is the same reason why vitrified ware does not hold up well
> outdoors in a freezing climate. The porosity of vitrified clay
> should be
> very low, but if there is any porosity at all, the clay can absorb
> water
> over time, and when that happens, the water cannot escape easily, in
> either
> heating above boiling, or cooling below freezing. It builds up
> pressure, and
> if the heating or cooling is extreme enough, the piece breaks.
>
> What happens in the case of freezing is just simple breakage, and
> however
> much we might bemoan the loss of the piece, it is of minor
> significance as
> compared to what happens when such a piece is heated and the
> impacted water
> turns to steam. It will build up more and more pressure until it
> exceeds
> the mechanical strength of the clay, and then ka-blam. I saw this
> happen in
> spectacular fashion to a large stoneware pitcher that had been
> sitting atop
> the firebox of our Bourry-box wood kiln. It was there when I
> arrived at the
> Craft Center in 1994. There is a minimal roof above that kiln, and the
> pitcher had apparently gathered water. During a firing about ten or
> twelve
> years ago, we had just gotten the first chamber to temperature and
> had moved
> around to the side of the kiln to fire the second chamber when the
> pitcher
> exploded like a small artillery shell. Chunks of that pitcher hit
> the walls
> of the building like bullets, and there was an incredible racket as
> they
> landed all up and down the shed that runs along the back of the
> building.
> Several windows were broken. If any of us had been in the line of
> fire, it
> could have been fatal. I really learned respect for the power of
> expanding
> steam from water impacted in a "vitrified" piece of clay. A
> vitrified clay
> piece that has been in regular contact with water should never be
> refired.
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft
> Tennessee Tech University
> vpitelka@dtccom.net; wpitelka@tntech.edu
> http://iweb.tntech.edu/wpitelka
Alice DeLisle on tue 19 oct 10
Thanks to Bill, Larry, Vince, Arnold and others for advice on how to deal w=
ith
the elements in my kiln. You have convinced me that water got into the por=
es of
this piece and the resultant steam caused it to disintegrate. I think that=
I am
still in shock about the number of tiny shards generated by the explosion a=
nd
the fact that the shards went everywhere in my kiln. Even though all of th=
e
work was ruined, my kiln is my biggest concern. It is a few years old, but=
in
my mind, it was new until yesterday! I vacuumed the kiln immediately, and =
I
spent this morning scraping shelves, but have not been able to return to th=
e
kiln triage just yet - keeping with the clinical theme. I needed the thera=
py of
making a couple of pots first.
Vince wrote:
When you say you were not happy with the glaze, how long had the piece been
sitting around after the initial glaze firing? Is there any chance that it
had water in it for any period of time? Was it sitting in an especially
damp or humid environment for a prolonged period? I have never heard of
such an explosion occurring just from water absorbed during glazing. Peopl=
e
re-glaze and re-fire things all the time.
I know, I have re-glazed many times. The piece that I re-fired was fired a=
bout
4 weeks ago. It had not had water in it. It was in my studio or my house =
the
entire time, and this is probably about the driest time of year around here=
. I
described the slabs in the construction previously, and the belt part that
covered the region where the explosion occurred was not glazed the first ti=
me
but was the second time so maybe it was the more porous part of the piece. =
It
was also an area where there were 2 and 3 layers of slabs and probably some=
air
pockets. The rest of the piece was glazed the first time, except the botto=
m, of
course. In preparation for re-glazing, I heated the piece to about 200oF. =
I
was just going to hold it by the bottom and dunk the top in the glaze bucke=
t but
it slipped out of my hand and fell in. I fished it out and let it dry over=
night
before cleaning off the bottom. It was at least another day, and maybe 2 d=
ays,
before I did the re-firing, so at least 2 days between glazing and firing. =
I
pre-heated the kiln at 200oF for 1 hr before the firing cycle. I routinely
pre-heat for at least 1 hr, and longer if I know some pieces might be wet.
Obviously, not enough this time.
Sandy Henderson on wed 20 oct 10
On October 18, Larry Kruzan wrote:
>About this kiln - Are you saying that you had full round shelves mixed wit=
h
>half shelves??? That's not good practice.
>
I am wondering why this is not okay. I have always used whatever shapes and=
sizes of shelves were handy and never observed a problem. Am I missing so=
mething that "everyone" knows? (Certainly quite possible.)
Sandy Henderson
Long-time lurker
Vince Pitelka on thu 21 oct 10
Alice DeLisle wrote:
"I know, I have re-glazed many times. The piece that I re-fired was =3D
fired
about 4 weeks ago. It had not had water in it. It was in my studio or =3D
my
house the entire time, and this is probably about the driest time of =3D
year
around here. I described the slabs in the construction previously, and =3D
the
belt part that covered the region where the explosion occurred was not
glazed the first time but was the second time so maybe it was the more
porous part of the piece. It was also an area where there were 2 and 3
layers of slabs and probably some air pockets. The rest of the piece =3D
was
glazed the first time, except the bottom, of course. In preparation for
re-glazing, I heated the piece to about 200oF. I was just going to hold =
=3D
it
by the bottom and dunk the top in the glaze bucket but it slipped out of =
=3D
my
hand and fell in. I fished it out and let it dry overnight before =3D
cleaning
off the bottom. It was at least another day, and maybe 2 days, before I =
=3D
did
the re-firing, so at least 2 days between glazing and firing. I =3D
pre-heated
the kiln at 200oF for 1 hr before the firing cycle. I routinely pre-heat =
=3D
for
at least 1 hr, and longer if I know some pieces might be wet. Obviously, =
=3D
not
enough this time."
Alice -=3D20
This narrows it down a lot. I always advise my students in classes and
workshops against laminating slabs against each other, especially in any =
=3D
way
that might trap air bubbles between the layers. Laminating small strips =
=3D
of
slab or small appliqu=3DE9s is a different situation altogether, but =3D
broader
areas of slab laminated together often cause trouble in drying and =3D
firing.
In this case, the piece survived bisque-firing just fine because air =3D
could
escape from those pockets. Once the piece was glazed, apparently the
primary escape avenues were closed off. In dropping the piece in the =3D
bucket
it probably introduced just enough moisture (especially through the =3D
bottom),
and when that moisture gathered as steam inside those air pockets, it =3D
was
enough to cause the explosion. =3D20
In the future, whenever you are going to reglaze an already-fired piece =3D
by
dipping, I recommend that you wax the bottom to reduce the chance of any
moisture soaking into the clay.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu=3D20
http://iweb.tntech.edu/wpitelka
Vince Pitelka on thu 21 oct 10
In response to an admonition against using half-round and full-round =3D
shelves together, Sandy Henderson wrote:
"I am wondering why this is not okay. I have always used whatever shapes =
=3D
and sizes of shelves were handy and never observed a problem. Am I =3D
missing something that "everyone" knows? (Certainly quite possible.)"
Hi Sandy. I was wondering the same thing, and I've been in this biz for =
=3D
40 years. There is no reason not to use half-round and full-round =3D
shelves together, as long as all shelves are supported evenly. The =3D
theory is that if you are using half-round shelves, you are using the =3D
standard three-point support system, usually with four posts to support =3D
two shelves - the normal "common-posting" system. If you change to a =3D
full-round shelf halfway up, you suddenly have four-point support, which =
=3D
doesn't work unless you use wadding on at least one post, because the =3D
shelf will almost never sit with even pressure on the four support =3D
points. If you didn't accommodate that and kept stacking more layers, =3D
that shelf could crack and cause the whole set to come tumbling down. =3D
It really is not much trouble to use wadding, so I don't see any =3D
problem. I would not mix half-round and full-round unless I used =3D
wadding. In such a situation, I just set the full-round shelf in place =3D
and see how it wobbles, and then put a little wadding on one post to =3D
stop the wobble. =3D20
I do not subscribe to the notion that half-shelves are better and that =3D
they should be staggered to even out the heat. With today's multi-zone =3D
controllers, and with the space around the outside of the shelves, there =
=3D
is no reason to take such unnecessary precautions, especially =3D
considering that it decreases the efficiency of stacking the kiln.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu=3D20
http://iweb.tntech.edu/wpitelka
William & Susan Schran User on thu 21 oct 10
On 10/20/10 9:54 PM, "Sandy Henderson" wrote:
> On October 18, Larry Kruzan wrote:
>> About this kiln - Are you saying that you had full round shelves mixed w=
ith
>> half shelves??? That's not good practice.
> I am wondering why this is not okay. I have always used whatever shapes a=
nd
> sizes of shelves were handy and never observed a problem. Am I missing
> something that "everyone" knows? (Certainly quite possible.)
No, you're not missing anything.
I can see Larry's point if the kiln has a single thermocouple that a
controller is reading and there is a full shelf that cuts the chamber such
that the thermocouple is above or below the full shelf one might see
slightly different results above and below the shelf - unless he is
addressing the number of posts used for mix of half and full shelves...
Don't know, he didn't write why.
I use full and half shelves.
Full shelf at bottom, mix of full & half shelves throughout the kiln.
I also have kilns with thermocouples at each section, so even temperatures
are not an issue.
Also have 28" kilns that only use half shelves.
So answer is yes and no, it all depends.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Larry Kruzan on thu 21 oct 10
Hi Sandy,=3D20
If a person is using mixed shelves and some how has all the posts lined up,=
=3D
one on top of another - there is no problem. However if the posts are not =
=3D
in line vertically, huge torque stresses build on the shelf. This will lead=
=3D
to eventual failure of the shelf, probably at a high temp, leaving a mess =
=3D
in the kiln.=3D20
The smaller the kiln and=3DC2=3DA0shelf is, the=3DC2=3DA0less the stress (s=
horter d=3D
istance across, less weight, etc.) and=3DC2=3DA0less likely you may have a =
fail=3D
ure.=3D20
In my 18" kiln, I could get away with bisque firings where it was unbalance=
=3D
d - but my 28" would collapse if I tried it once. I don't even want to thin=
=3D
k about trying it in one of my gas kilns.=3D20
If you have a kiln owners manual, please read the stacking directions. I kn=
=3D
ow Skutt has them posted on-line.=3DC2=3DA0 www.Skutt.com =3DC2=3DA0Should =
get you =3D
there.=3D20
I'm glad you have never had a problem. Perhaps you get the posts close enou=
=3D
gh or you have a small kiln or you've just been lucky. To me it's like text=
=3D
ing while driving - you might get away with it for years, but sooner or lat=
=3D
er a car is going to stop short in front of you - you know the rest.=3D20
Larry=3D20
----- Original Message -----=3D20
From: "Sandy Henderson" =3D20
To: Clayart@LSV.CERAMICS.ORG=3D20
Sent: Wednesday, October 20, 2010 8:54:11 PM=3D20
Subject: Re: Kiln Cyclone=3D20
=3DC2=3DA0=3D20
On October 18, Larry Kruzan wrote:=3D20
>About this kiln - Are you saying that you had full round shelves mixed wit=
=3D
h=3D20
>half shelves??? =3DC2=3DA0That's not good practice.=3D20
>=3D20
I am wondering why this is not okay. I have always used whatever shapes and=
=3D
sizes of shelves were handy and never observed a problem. =3DC2=3DA0Am I m=
issi=3D
ng something that "everyone" knows? (Certainly quite possible.)=3D20
Sandy Henderson=3D20
Long-time lurker=3D20
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