Gillian Parke on sun 2 dec 01
Back in September, I had a catastrophic glaze firing
using Aardvark Bee Mix. Upon opening in kiln, I found
that approx. 30 pots had completely melted. The clay
looked like a candle that had melted and dripped off
the side of a table. Pots that had not melted were
destroyed from the melted clay running into it or onto
the shelves below. My immediate assumption was that I
was mistakenly sold cone 5 instead of cone 10 clay.
At the time, I did not bisque fire my own pots but the
potter that did used a Skutt kiln with controller
using the fast bisque schedule. The lid and port
holes were open until 1000F and then lid was closed
and all ports closed except the top.
Samples were sent to Aardvark for analysis. I was
sent the following results:
As I states before, the majority of problems with the
fired results of pottery are the result of
insufficient oxidation of the ware during the bisque
firing. From 700-1200F, there must be ample oxygen
and time to form CO2 gas. As a gas, the carbon will
vacate the ware. If there is not enough oxygen and
time present to remove the carbon, it will stay in the
ware and take oxygen from the iron present in the
ware. The iron will change from Fe2O3 to FeO. FeO is
en extremely strong flux and from our testing and past
experience, this is probably the cause of the melting
shown in the customer's sample.
As a chemist, this explanation makes alot of sense.
However, every potter that I speak to, has never heard
of such an occurance and thinks the explanation is
bull !@#$. I would greatly appreciate others thoughts
on the subject. I continue to use Bee Mix because I
love the way it throws. Now I bisque fire myself,
closing the lid around 1300F with a 12-13hour firing
time. So far, no problems.
Thanks
Gillian
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Tom Wirt/Betsy Price on mon 3 dec 01
Hi Gillian...
Yes, their explanation came from the back end of a cow. First, B-Mix
is essentially a white body...very little iron. And even if you had
that much iron and did that much reduction, you might have gotten
slumping, but certainly no meltdown.
I would suggest that what you actually got was low fire clay, not even
cone 5. Once we accidentally put a lowfire clay in our cone 10 firing
and the result was exactly as you described melted candle wax that ran
down shelves and into other pots.
I'd suggest an experiment....put a large cone 05 and a large cone 5 on
a slab and fire them in your next firing. You'll see the level of
melting that takes place. Even with five cones overfiring, I'd guess
that you would still have a pot shape.
Aardvark has always been good to deal with for me. Sounds like
someone just screwed up and you got it.
Tom Wirt
Subject: Bee Mix, melt down, and bisque firing
| Back in September, I had a catastrophic glaze firing
| using Aardvark Bee Mix. Upon opening in kiln, I found
| that approx. 30 pots had completely melted. The clay
| looked like a candle that had melted and dripped off
| the side of a table.
Ron Roy on mon 3 dec 01
This does not make sense to me - for the iron to be converted to a flux it
has to be there - as I understand it - B mix is a white firing clay.
Even in a body with some iron - I would not expect this kind of melting -
maybe some bloating or blebbing but not melting like that.
I would expect this kind of melting from a lowfire clay fired to cone 10.
The question which might shed some light here is - how far did your cone 10
fall???
RR
>As a chemist, this explanation makes alot of sense.
>However, every potter that I speak to, has never heard
>of such an occurance and thinks the explanation is
>bull !@#$. I would greatly appreciate others thoughts
>on the subject. I continue to use Bee Mix because I
>love the way it throws. Now I bisque fire myself,
>closing the lid around 1300F with a 12-13hour firing
>time. So far, no problems.
>
>Thanks
>Gillian
>
>__________________________________________________
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>Buy the perfect holiday gifts at Yahoo! Shopping.
>http://shopping.yahoo.com
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>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.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Ababi on mon 3 dec 01
You mix me up
Is the B mix clay or honey
Is tea material for T pots or raku?
Ababi
Marianne Lombardo on mon 3 dec 01
Gillian
I would be interested in see what others reply to this. Mainly I'd like
some confirmation on what temp the carbon gas escapes the ware. I had read
elsewhere that the critical temp was from 1200F-1400F. I was looking at it
from the pinholing aspect. I did pose a question about it, but the only
reply I received was some unknown address with an attachment so I deleted
it.
> Samples were sent to Aardvark for analysis. I was
> sent the following results:
>
> As I states before, the majority of problems with the
> fired results of pottery are the result of
> insufficient oxidation of the ware during the bisque
> firing. From 700-1200F, there must be ample oxygen
> and time to form CO2 gas. As a gas, the carbon will
> vacate the ware. If there is not enough oxygen and
Marianne
Snail Scott on mon 3 dec 01
At 07:24 PM 12/2/01 -0800, you wrote:
...If there is not enough oxygen and
>time present to remove the carbon, it will stay in the
>ware and take oxygen from the iron present in the
>ware. The iron will change from Fe2O3 to FeO. FeO is
>en extremely strong flux and from our testing and past
>experience, this is probably the cause of the melting
>shown in the customer's sample.
Sounds like hooey to me! Isn't Bee Mix a white clay?
I've seen the fluxing effects of iron in red clay
bodies, but even then, it drops the firing temperature
only by a cone or two at most. (And I've done a few
way-too-fast single-fire reduction firings with no
bisque at all, using clay bodies made of 30% Redart!)
Surely the trace iron present in Bee Mix is nowhere
near enough to account for such a meltdown. On the
other hand, it sounds exactly like the scene I saw
in college, when a student brought in clay from
elsewhere, put it in a ^10 firing, and it turned out
to be a ^5 body. (and a very high-iron one, too.) It
looked like Dali had painted the stuff!
-Snail
Andi Fasimpaur on mon 3 dec 01
At 07:24 PM 12/2/01 -0800, Gillian Parke wrote:
>Back in September, I had a catastrophic glaze firing
>using Aardvark Bee Mix. Upon opening in kiln, I found
>that approx. 30 pots had completely melted. The clay
>looked like a candle that had melted and dripped off
>the side of a table. Pots that had not melted were
>destroyed from the melted clay running into it or onto
>the shelves below.
When I was 17 I got a job as the studio monitor for
a local clay co-op. There was an old alpine in the
studio, and there were only a few people who knew
how to fire it. I was slowly learning by assisting those
who knew and for this one particular firing, one of the
co-op members, who had a fondness for buff clays
and had bags and bags of both high-fire and mid-range
clay which she never bothered to label, was complaining
that none of her work was in the kiln. I explained that
the firing for which we were loading the kiln had been
paid for by another potter, that it was production work
for a show, that he needed to get as much of his
work into the kiln as possible, and that, frankly, we
couldn't take the risk of having one of her mid-range
pieces end up in the kiln.
Chris was still trying to get the hang of where the
best reduction spots were in the kiln and he took a
couple of Polaroids before we closed the kiln and
headed home for the night. The next day, Saturday,
we came in and fired the kiln. When I came in on
Sunday morning, Chris wasn't there yet so I peeked
in the spyhole because my curiosity was killing me.
What I saw seemed so surreal that, in spite of what
had come to seem good etiquette, I opened the kiln
even though the person responsible for the firing
wasn't there. Chris arrived to find me sitting on the
floor, my head in my hands, crying... it looked like
an accident in a candle factory. As Chris was
looking at his polaroids, trying to figure out what had
gone wrong, I noticed several of his glazed pots
sitting on the ware shelves... judging by where those
should have been, according to the photos, the
pots which melted were placed in the kiln in place
of the ones which were sitting, unfired, on the ware
shelves...
I was responsible for all of the bisque firing in that
studio, I used the exact same firing schedule for
all of the bisque loads I did, the work of all of the
potters in the co-op was usually co-mingled in bisque
loads... I cannot believe that improper bisque firing
was to blame for this incident... I can only assume,
as I have since opening that kiln 16 years ago, that
the woman who was complaining about her pots not
going into the "big kiln" and whose same pots were
missing while pots which we had loaded into the kiln
and photographed in place were sitting on the ware
shelves, had place midrange buff stoneware pieces
in the ^10 firing, that they melted, and that they were
responsible for destroying all but 6 pieces in that
kiln.
>As a chemist, this explanation makes alot of sense.
>However, every potter that I speak to, has never heard
>of such an occurance and thinks the explanation is
>bull !@#$. I would greatly appreciate others thoughts
>on the subject. I continue to use Bee Mix because I
>love the way it throws. Now I bisque fire myself,
>closing the lid around 1300F with a 12-13hour firing
>time. So far, no problems.
This is the first I've ever heard of this. I often feel as though
I would need a background in geology to understand some
of the mineral development / state and body changes which
occur in firing... but that said, it seems a very unlikely
occurance... and a 12-13 hour bisque schedule seems like
a huge investment of time and/or feul...
Andi.
http://www.mysticspiral.com
Steve Mills on tue 4 dec 01
I have also met the same problem via a friend of mine: he used to have
his clay made up for him, he preferred it that way because it saved him
time. His recipe included a small (0.50) amount of Nephaline Syenite,
however on one occasion the manufacturer missed out the decimal point,
with results identical to those described. A very expensive mess: not
only was the charge lost, but all the furniture associated with it!
Steve
Bath
UK
In message , Tom Wirt/Betsy Price writes
>Hi Gillian...
>
>Yes, their explanation came from the back end of a cow. First, B-Mix
>is essentially a white body...very little iron. And even if you had
>that much iron and did that much reduction, you might have gotten
>slumping, but certainly no meltdown.
>
>I would suggest that what you actually got was low fire clay, not even
>cone 5. Once we accidentally put a lowfire clay in our cone 10 firing
>and the result was exactly as you described melted candle wax that ran
>down shelves and into other pots.
>
>I'd suggest an experiment....put a large cone 05 and a large cone 5 on
>a slab and fire them in your next firing. You'll see the level of
>melting that takes place. Even with five cones overfiring, I'd guess
>that you would still have a pot shape.
>
>Aardvark has always been good to deal with for me. Sounds like
>someone just screwed up and you got it.
>
>Tom Wirt
>
>
>Subject: Bee Mix, melt down, and bisque firing
>
>
>| Back in September, I had a catastrophic glaze firing
>| using Aardvark Bee Mix. Upon opening in kiln, I found
>| that approx. 30 pots had completely melted. The clay
>| looked like a candle that had melted and dripped off
>| the side of a table.
--
Steve Mills
Bath
UK
John Baymore on wed 5 dec 01
As I states before, the majority of problems with the
fired results of pottery are the result of
insufficient oxidation of the ware during the bisque
firing. From 700-1200F, there must be ample oxygen
and time to form CO2 gas. As a gas, the carbon will
vacate the ware. If there is not enough oxygen and
time present to remove the carbon, it will stay in the
ware and take oxygen from the iron present in the
ware. The iron will change from Fe2O3 to FeO. FeO is
en extremely strong flux and from our testing and past
experience, this is probably the cause of the melting
shown in the customer's sample.
Gillian,
While the above general concept is absolutely technically true........
there would have to be an AWFUL lot of Fe2O3 present in the claybody to
have the effect of overfluxing the body to the extent that you describe i=
n
the melted pots scenario. All the iron is not only an active flux on
silica....it imparts color too. So the effect of that also should serve =
to
significantly darken the body. Not to mention that if it were there in
large quantities..... even in the Fe2O3 state.... it would darken the bod=
y.
B-mix is white isn't it? So was the raw clay significantly darker than=
usual? The fired mess? If not....... then the iron probably was in the
normal range for that body....... which in a white body is a pretty small=
inclusion. If it is still white...... look to a different culprit.
Sounds like it is stretching things a bit to me.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop 2002 Dates TBA"=
Gillian Parke on thu 6 dec 01
John and friends,
Thanks for your input. The chemistry part of the
explanation made sense to me but that was about all.
When throwing my pots, I never noticed anything
different. However, after the bisque fire, there was
dozen or so pots that had a different color and
texture than the others (approx 25lb worth of pots).
Instead of being white, the pots were slightly dry and
the texture didn't seem as pores. When I waxed the
bottom, instead of turning pinkish, the waxed clay
looked grey.
The kiln was fired to cone 9 down, cone 10 falling.
When I spoke with Scott at Aardvark, I said how such a
catastrophic event didn't make sense even assuming
that all the Fe2O3 was converted to FeO. But he
assured me that indeed it would happen and that he has
seen the something happen to other potters. He
implied that all most of the Fe2O3 in the clay would
be converted because bee mix has such a high organic
carbon content. The other thing I was told was that
if I took the "incorrectly" bisque pots, refired to
cone 06 with proper amount of O2, then the FeO would
convert back to Fe2O3 and things should be fine.
Well, I took a bowl that was the funny color, fired it
twice on the top shelf with lid open to cone 06 and
there is no noticeable difference. I have not put it
in the glaze firing yet.
I fact that the pieces added up to about 25-50lb of
clay and that the porosity at cone 06 seemed off,
leads me to believe that there was something indeed
wrong with the clay. Is there a was to tell the
difference between cone 10 clay and cone X clay at the
bisque stage? Is there an independent lab the I could
send it to? Aardvark tested samples from the 400lb
that I bought and returned but I think there was only
one bad box or bag of clay and I used it all up. I
appreciate any help in this rather complicated mess.
Gillian
--- John Baymore wrote:
>
> As I states before, the majority of problems with
> the
> fired results of pottery are the result of
> insufficient oxidation of the ware during the bisque
> firing. From 700-1200F, there must be ample oxygen
> and time to form CO2 gas. As a gas, the carbon will
> vacate the ware. If there is not enough oxygen and
> time present to remove the carbon, it will stay in
> the
> ware and take oxygen from the iron present in the
> ware. The iron will change from Fe2O3 to FeO. FeO
> is
> en extremely strong flux and from our testing and
> past
> experience, this is probably the cause of the
> melting
> shown in the customer's sample.
>
>
> Gillian,
>
> While the above general concept is absolutely
> technically true........
> there would have to be an AWFUL lot of Fe2O3 present
> in the claybody to
> have the effect of overfluxing the body to the
> extent that you describe in
> the melted pots scenario. All the iron is not only
> an active flux on
> silica....it imparts color too. So the effect of
> that also should serve to
> significantly darken the body. Not to mention that
> if it were there in
> large quantities..... even in the Fe2O3 state.... it
> would darken the body.
> B-mix is white isn't it? So was the raw clay
> significantly darker than
> usual? The fired mess? If not....... then the iron
> probably was in the
> normal range for that body....... which in a white
> body is a pretty small
> inclusion. If it is still white...... look to a
> different culprit.
>
> Sounds like it is stretching things a bit to me.
>
> Best,
>
> ..............................john
>
> John Baymore
> River Bend Pottery
> 22 Riverbend Way
> Wilton, NH 03086 USA
>
> 603-654-2752 (s)
> 800-900-1110 (s)
>
> JohnBaymore.com
>
> JBaymore@compuserve.com
> John.Baymore@GSD-CO.com
>
> "Earth, Water, and Fire Noborigama Woodfiring
> Workshop 2002 Dates TBA"
>
______________________________________________________________________________
> 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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Ron Roy on thu 13 dec 01
This also is untrue - once the Fe2O3 is converted it is very difficult to
convert it back again. Besides - you have to have enough iron in the clay
to get lots of melting and there just isn't in a white body.
Ardvark should understand - they are not doing themselves a favour but
fixing on an inappropriate explanation - I suggest you forward some of the
answers you got on ClayArt to the owner of Ardvark and refer them to the
Hamer book for confirmation.
Pity - they are one of the few companies that do some testing - it does no
good if you blame poor clay performance on the potter however.
It is a good policy to write the batch numbers on your bill - or somewhere
- at least you have something to go back with. If they are testing ask to
see the results.
When we get a complaint about clay the first thing we do is go to the test
data - if the clay tested out normal - we then have to look at other
causes.
RR
The other thing I was told was that
>if I took the "incorrectly" bisque pots, refired to
>cone 06 with proper amount of O2, then the FeO would
>convert back to Fe2O3 and things should be fine.
>Well, I took a bowl that was the funny color, fired it
>twice on the top shelf with lid open to cone 06 and
>there is no noticeable difference. I have not put it
>in the glaze firing yet.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
| |
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