karen terpstra on mon 11 feb 02
Hi all,
Just when you think you have it licked... We were put through the test
last weekend on that 7th firing. Like I mentioned earlier we fought the
weather--low pressure system all weekend. We also had oak barely a year
old and somewhat wet. It was not cured to where we like to see it. But,
it was not a problem the previous firing when we had good weather so I
didn't think to much about it.
Well we opened and had a few good pots but lost more than we ever had.
I'll list the problems and then what I think:
1. We had an unusual amount of bloating on both stoneware and
porcelain. I always bisque to only cone 010 because I think the body
gets more flashing that way. Have not had this bloating problem before
with either of my claybodies. The people who bisqued hotter didn't have
a much bloating---hardly any.
2. What a stuck together mess in parts of the kiln. We previously had
been so happy with our wadding of EPK/Alumina and the Zirconium stuff
kiln wash. We all did an unusual amount of grinding this time.
3. Salt chamber was just too glassy and we were especially careful to
hold that chamber back. you would think we fired to cone 14. We
didn't. It varied from cone 10 to 12 back there.
What I think:
1. bisquing to only 010 contributed to the bloating problem. And, there
had to be lots of early reduction happening that we weren't aware of in
the early part of the firing. I will bisque higher to see if it makes
any difference and be safer.
2. In the middle to last 2/3's of the firing we noticed big trouble. We
saw the wood was burning down to the grates but the firebox was still
filled with unburned Carbon Dioxide swirling around. We opened extra
bricks in front for more air (primaries and secondaries were already
open.) and closed the passives for more draught. Some people talk about
hydrogen reduction....we didn't know what to do with it! We were
unaware of what the low pressure system and our wet wood was doing to
us.
3. We started to salt the second chamber at cone 8/9 with a mixture of
salt/soda mixed with water (yup...just what we needed right?). We took
one of the 1st salt rings out and the top was shiny and one side and
bottom had a guncky black material on it. Never seen anything like it.
looked like little bits of coal had attached itself to the little ring.
We knew it was not silicon carbide and nothing from the wall or arch. I
took us longer to reach cone 10-12 than normal so maybe the salt and
carbon had time to do funny things.
When we unloaded, we noticed the black gunk around some of the heavily
salted areas. Work in those areas were glassy and stuck to the shelf
with more black gunk. (We don't salt more than 8 pounds in that
chamber.) We had just a little carbon coring on just a few pots too.
Just way too much water I think.
You experience people, is my thinking right?
We are stock piling LOTS of oak wood now to stay ahead for 2 years. I'm
still convinced the kiln works like a dream but demands really good
cured wood. I like to sit in my chair and relax when I fire and not
worry about any of the above! In the mean time I'm going after some red
shino in the gas kiln and fire the wood kiln when the weather man says
it's safe.
Happy firings,
Karen Terpstra
UW-L
David Hendley on mon 11 feb 02
Dear Karen, just to stir the pot, some comparisons to
my firing experiences:
I often long for a good low pressure system to settle in before
I fire my kiln. In the summer in Texas they can be few and far
between. This weather produces the best results by giving
a good even reduction throughout the kiln (I think).
In the summer, it takes my oak wood about 2 or 3 months to
dry, twice that in the winter. If I use all very dry wood my
firing suffers from going too fast and not getting enough
reduction. I will mix in some semi-wet wood if it seems too dry.
Many, maybe most, people who fire with wood don't bisque
fire at all.
I wouldn't even think of sitting in a chair and relaxing when
I fire the kiln.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "karen terpstra"
To:
Sent: Monday, February 11, 2002 12:38 PM
Subject: The importance of cured wood
> Hi all,
> Just when you think you have it licked... We were put through the test
> last weekend on that 7th firing. Like I mentioned earlier we fought the
> weather--low pressure system all weekend. We also had oak barely a year
> old and somewhat wet. It was not cured to where we like to see it. But,
> it was not a problem the previous firing when we had good weather so I
> didn't think to much about it.
>
> Happy firings,
> Karen Terpstra
> UW-L
>
Tony Ferguson on tue 12 feb 02
Greetings,
I had visited your work months back was very excited. I wood fire as well
mainly shino and ash glazes--looking for a good black and flashing slip. I
single fire my work actually and am always on the quest to try new things
that will fit my body and way of firing. I usually fire my anagama by
myself for 20 - 30 hours.
You have many amazing works, both in majolica and woodfire. Would you
consider sharing any of your recipes? I especially liked
"Woodfired Jar, Avian Life"
thrown constructed stenciled stoneware
flashing slip, !3.5", 34cm.,
and black glaze
"Sunken Vessel" Vessel
helmer stoneware, feldspar stones,
woodfired, tumble stacked,
"Japanese Maple Covered Jar"
thrown altered stoneware feldspar
stones stencils slip trailed, 12.5", 32cm. $240
"From the Bottom of the Sea"
thrown stoneware, flashing slip, tumble
stacked, cone 11, 8.5", 21cm
These are to die for!
"Bizen Style Water Jar"
thrown red stoneware, feldspar stones, reduction
cooled, willow ash, tumble stacked, 10", 25cm.,
Artist's collection, as seen on the cover of
"Sharpei Hanging Flower Vase"
thrown stoneware, flashing slip, feldspar
stones, willow ash, 6", 15cm., $100
I have really enjoyed your work! Of course, should you be interested in any
of my glazes, I am happy to share.
Thank you!
Tony Ferguson
Stoneware, Porcelain, Raku
www.aquariusartgallery.com
Photographic, Web Site, & Marketing Services for Artists
218-727-6339
315 N. Lake Ave
Apt 401
Duluth, MN 55806
----- Original Message -----
From: "Richard Selfridge"
To:
Sent: Tuesday, February 12, 2002 6:56 PM
Subject: The Importance of Cured Wood
> Karen's report of her last wood firing suggests a multitude of problems
and
> possible causes--sort of a definition of woodfiring. In her latest post
she
> said--
> "I really don't have any idea about how many people bisque or not for the
> wood fires. I'm sure it depends on the type of kiln and how they want
> to fire for the effects they want. We do it because we want to bring the
> temperature up fast as we can and then soak for a period of time within
> 30-34 hours. We are after flash. So I think that depends on your kiln
> and firing schedule. My experience with an anagama was to sl-o-w-l-y
> bring the temp up for even temperature and that made it easy to put
> greenware in the back."
>
> Some thoughts occur to me about bisque firing, flashing, bloating and
black
> coring.
> 1) I suspect that a soft cone 010 bisque does promote flashing but I have
> never done a critical test. It does seem reasonable as we know that shinos
> and other soda or Neph sy glazes start to melt and trap carbon at this
temp.
>
> 2) My guess is that the kind of bisque firing, fast or slow, has more to
do
> with the bloat/black core problem. Mick Casson said years ago when he was
> in Edmonton that their once fired ball clay based body, fired in their
wood
> kiln, needed to be stalled and held for at least an hour at 800C to burn
> out the carbon which is usually associated with the ball clays. If you
> don't bisque slowly at the top end of a bisque firing you don't get the
> lignite burnt out of the clay and it causes trouble in the glaze firing.
> This is a common fault for majolica earthenware as the gassing off thru
the
> glaze leaves little white stars.
>
> 3)Another issue on "to bisque or not to bisque" depends if you want to
> tumble stack. Some bodies do shrink in the bisque firing and if you try to
> load the kiln tight to the ceiling of the chamber the stack shrinks so
much
> in the once firing that the fire is harder to keep on the floor. The less
> shrinkage in the glaze firing, the better chance that things will come
> apart after the firing where wadded.
>
> 4)It is not clear to me exactly when the "flash" starts in a wood firing.
I
> suspect that it is early on and that rushing the firing to then soak at
top
> temperature for a long time may not get maximum flash. I think the flash
> comes from the volatiles from the potassium and sodium in the wood and
that
> they move thru the kiln and affect the colour well before any ash either
> sticks and or melts. An article by Wil Shynkaruk and Jason Hess
> "Woodfiring in the Desert: The Cottonwood Conundrum" in vol 9 of Ceramics
> Technical sheds some light on this subject.
>
> 5)Getting wads apart in a long firing with lots of volatiles can be a
> problem with the alumina/EPK type wads. Better to use coarse fireclay,
> coarse silica sand, flour,and saw dust. This approach produces a more
> crumbly wad which doesn't need as much grinding. See the article on our
web
> site "Ah, So You Do It for the Ash" http://www.selfridgeceramicart.ca
>
> All of these issues, while fascinating, don't give any clear direction on
> whether early heavy reduction is a good idea or not. If you don't reduce
> the shinos early on they are often pastey but too much reduction early on
> often results in black core and bloats especially with high iron glazes.
>
> Regards and happy testing, Richard and Carol Selfridge
> http://www.selfridgeceramicart.ca
>
>
____________________________________________________________________________
__
> 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.
>
karen terpstra on tue 12 feb 02
Hi David,
Your response made me grin. How easy it is to forget that all of our
kilns are as different as night and day, fired for different results, as
different as you and me...condsidering the gender difference. But
granted there are commonalities---we are both tall. There are probably
some commonalties with our kilns too---they both burn wood.
But seriously, the oak up here takes 2 years at most to cure. Yawl down
in Texas have dry air all year around for the most part, right? We have
hot humid summers and cold wet winters. And, I'd like to compare the
barometric pressure readings on our firing days. And, If I don't get
the wood under a roof, it gets inches and inches of rain or piled under
inches and inches of snow.
I don't mind firing with wet wood. In fact, I agree, when the kiln is
flying and you need to hold it back it's nice to throw in some wet wood.
But, when the wood is not cured AND is wet, I have a problem. There is
a big difference between uncured wood (we also call it green) and cured
wood that is wet.
I really don't have any idea about how many people bisque or not for the
wood fires. I'm sure it depends on the type of kiln and how they want
to fire for the effects they want. We do it because we want to bring the
temperature up fast as we can and then soak for a period of time within
30-34 hours. We are after flash. So I think that depends on your kiln
and firing schedule. My experience with an anagama was to sl-o-w-l-y
bring the temp up for even temperature and that made it easy to put
greenware in the back. but you know all this...
And about sitting in a chair...When my stock pile of wood is good and
cured you may come up and fire with us. I will sit in my chair with my
cigar ;) and watch you stoke. Actually, if I don't force myself to
relax during a firing, I get all riled up over every little thing....not
a pretty sight.
Happy firings
Karen Terpstra
La Crosse, WI
karen terpstra on tue 12 feb 02
David Hendley wrote:
> I often long for a good low pressure system to settle in before
> I fire my kiln....I will mix in some semi-wet wood if it seems too dry...
>
The advanced class and I were still musing over our last firing and I
read them your post--the one in response to mine. They would like to
invite you to fire up here with us using our wet, uncured oak, maybe
even throw in a little cedar--the type from Minnesota that doesn't
burn...We will check the weather forecast and let you know when an early
summer storm rolls in with extremely low pressure, lightning, tornadoes
and all, maybe even some hail. Actually quite exciting! You can be
sure I will be sitting in my chair while you stoke and stir, stoke some
more, clean out mouse holes, then stoke again to you hearts
content...for 30 hours or more...and with a crew of mostly inexperienced
students. :)
Happy firings--wet or dry,
Karen Terpstra
La Crosse, WI
Richard Selfridge on tue 12 feb 02
Karen's report of her last wood firing suggests a multitude of problems and
possible causes--sort of a definition of woodfiring. In her latest post she
said--
"I really don't have any idea about how many people bisque or not for the
wood fires. I'm sure it depends on the type of kiln and how they want
to fire for the effects they want. We do it because we want to bring the
temperature up fast as we can and then soak for a period of time within
30-34 hours. We are after flash. So I think that depends on your kiln
and firing schedule. My experience with an anagama was to sl-o-w-l-y
bring the temp up for even temperature and that made it easy to put
greenware in the back."
Some thoughts occur to me about bisque firing, flashing, bloating and black
coring.
1) I suspect that a soft cone 010 bisque does promote flashing but I have
never done a critical test. It does seem reasonable as we know that shinos
and other soda or Neph sy glazes start to melt and trap carbon at this temp.
2) My guess is that the kind of bisque firing, fast or slow, has more to do
with the bloat/black core problem. Mick Casson said years ago when he was
in Edmonton that their once fired ball clay based body, fired in their wood
kiln, needed to be stalled and held for at least an hour at 800C to burn
out the carbon which is usually associated with the ball clays. If you
don't bisque slowly at the top end of a bisque firing you don't get the
lignite burnt out of the clay and it causes trouble in the glaze firing.
This is a common fault for majolica earthenware as the gassing off thru the
glaze leaves little white stars.
3)Another issue on "to bisque or not to bisque" depends if you want to
tumble stack. Some bodies do shrink in the bisque firing and if you try to
load the kiln tight to the ceiling of the chamber the stack shrinks so much
in the once firing that the fire is harder to keep on the floor. The less
shrinkage in the glaze firing, the better chance that things will come
apart after the firing where wadded.
4)It is not clear to me exactly when the "flash" starts in a wood firing. I
suspect that it is early on and that rushing the firing to then soak at top
temperature for a long time may not get maximum flash. I think the flash
comes from the volatiles from the potassium and sodium in the wood and that
they move thru the kiln and affect the colour well before any ash either
sticks and or melts. An article by Wil Shynkaruk and Jason Hess
"Woodfiring in the Desert: The Cottonwood Conundrum" in vol 9 of Ceramics
Technical sheds some light on this subject.
5)Getting wads apart in a long firing with lots of volatiles can be a
problem with the alumina/EPK type wads. Better to use coarse fireclay,
coarse silica sand, flour,and saw dust. This approach produces a more
crumbly wad which doesn't need as much grinding. See the article on our web
site "Ah, So You Do It for the Ash" http://www.selfridgeceramicart.ca
All of these issues, while fascinating, don't give any clear direction on
whether early heavy reduction is a good idea or not. If you don't reduce
the shinos early on they are often pastey but too much reduction early on
often results in black core and bloats especially with high iron glazes.
Regards and happy testing, Richard and Carol Selfridge
http://www.selfridgeceramicart.ca
Merrie Boerner on tue 12 feb 02
Hi Karen,
I have used dry wood, wet wood, cedar, cypress, Magnolia, pecan, pine,
and road kill....for the fun of it. We say, "Try everything." and "It's ALL
good." here, on Hog Chain.
Once, during the pouring rain, I uncovered the wood to discover that the
tarps were as flimsy as cheese cloth and the wood was soaked. We moved it up
against the kiln, then in front of the fire box.....hardest firing we ever
had....but, the pots were full of surprises.
My last firing the wood was dry, red oak. ....Easiest firing we've had
as far as raising temp. We also split it into smaller sticks, which helped,
I'm sure....but, the pots were very predictably pretty....no
surprises.....I'm in for the surprises.
Finding that happy medium would be like firing in the perfect world.
Wood is one of the most challenging variables. Nils told me that during
a recent firing of a "train kiln", they cut down a small pine tree (I think
he said pine) and stoked it at the end of the three day firing. He said it
gave wonderful reduction results. Every time we fire here, my trees start to
shake in their roots.
See you soon,
Merrie
Who sits down during a firing ?!? If we are not stoking, we are dancing !
Well....maybe we sit for a spell......I just don't remember the sitting down
time.
Karen Terpstra on wed 13 feb 02
> From: Richard Selfridge
> Karen's report of her last wood firing suggests a multitude of
> problems and
> possible causes--sort of a definition of woodfiring.
Hi Richard,
Ok folks, enough now about my weird firing. I'm moving on... but what
a learning experience each wood firing is! And I've made note of all
the posts.
Richard, I'm putting your post in my "Things to think about before my
next firing" folder. It's becoming quite a thick folder. Haven't
looked up the article yet but will do it as soon as class is over today.
I will bring a gorgeous cup to the Clayart room that came out of this
firing but it has the bottom of it covered in that black, charcoaly,
mysterious, gunk. Maybe someone will have further insight. I hope!!!
( I promise it will not be part of the Clayart Mug exchange)
Thinking about a fantasy firing. David Hendley is up here trying to
fire with uncured and wet wood. Merrie is dancing around the kiln
trying to get in some stokes between David's. I'm fighting over my
chair with Mel. Kurt is here analyzing each move. And, we are all
smoking cigars and pretending to know everything.
.....oooh. fantasy or nightmare?
I'm going to make a note next time how much time I actually do spend in
that chair. ;)
thanks everyone!
Karen Terpstra
University of Wisconsin-La Crosse
ps. My husband wants to buy a cabin in Canada when we retire but how can
I put up with wood that takes THREE years to dry!!!
David Hendley on wed 13 feb 02
Dear Karen, I would invite your class down to Texas to help
me fire my kiln, but I'm afraid they might not leave. We are up
to 240 connections on Maydelle Water Supply, and I don't
know how many more newcomers we can handle.
Well, on second thought, if they come in August, after 20
consecutive days of 100 degrees plus, with not a cloud in the
sky for 2 weeks, they will have new appreciation for storms, ice
and snow, wet wood, and Wisconsin.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "karen terpstra"
To:
Sent: Tuesday, February 12, 2002 6:01 PM
Subject: Re: The importance of cured wood
> David Hendley wrote:
>
> > I often long for a good low pressure system to settle in before
> > I fire my kiln....I will mix in some semi-wet wood if it seems too
dry...
> >
> The advanced class and I were still musing over our last firing and I
> read them your post--the one in response to mine. They would like to
> invite you to fire up here with us using our wet, uncured oak, maybe
> even throw in a little cedar--the type from Minnesota that doesn't
> burn...We will check the weather forecast and let you know when an early
> summer storm rolls in with extremely low pressure, lightning, tornadoes
> and all, maybe even some hail. Actually quite exciting! You can be
> sure I will be sitting in my chair while you stoke and stir, stoke some
> more, clean out mouse holes, then stoke again to you hearts
> content...for 30 hours or more...and with a crew of mostly inexperienced
> students. :)
>
> Happy firings--wet or dry,
> Karen Terpstra
> La Crosse, WI
John Christie on wed 13 feb 02
In answer to Karen Terpstra's post, Richard Selfridge
wrote
>>4)It is not clear to me exactly when the "flash" starts in a wood firing.
I
>suspect that it is early on and that rushing the firing to then soak at top
>temperature for a long time may not get maximum flash. I think the flash
>comes from the volatiles from the potassium and sodium in the wood <<
It is quite instructive to fire some small unglazed bowls half-filled with
different wood ashes in a gas kiln and look at the flashing produced. As
you might expect, different wood ashes give different results varying from
black gunge to shiny opaque glass to dry white powder. What is more
surprising is the degree and quality of flashing on the inside of the bowls
associated with different wood ashes - which might give an indication of
which wood to favour in a particular firing. What I found most interesting
however was that tests using well-washed wood ash displayed little or no
flashing at all. This would support Richard's suggestion that the flashing
is more to do with soda/potash (the soluble salts removed in the washing)
than fly ash produced by all that riddling.
But what about the "black gunge" mentioned by Karen Terpstra? I have
suffered from this too - is it associated with excessive fuel/carbon in the
later stages of the firing? And even worse, what about the rough
(sometimes, but not always, black) stuff like coarse emery paper on one side
of the pot? It would be nice to have an explanation but I would settle for
knowing how to avoid these horrors!
John Christie,
Moray, Scotland
Julie Milazzo on thu 14 feb 02
Just an addition to the roadkill comment for those who
will be induced to try it: it is okay to fire roadkill
in a gas kiln, but it must be completely dessicated if
it is to be fired in an electric kiln. I do not know
this from personal experience, but had a nitwit of a
boss who stuck a (fresh) dead cat in a bisque firing.
It can still be smelled whenever the kiln is on, and
the thick juicy black residue on the firebrick is a
sight to behold... I'm nearly gagging remembering
those times. Julie
--- Merrie Boerner wrote:
> Hi Karen,
> I have used dry wood, wet wood, cedar, cypress,
> Magnolia, pecan, pine,
> and road kill....for the fun of it. We say, "Try
> everything." and "It's ALL
> good." here, on Hog Chain.
> Once, during the pouring rain, I uncovered the
> wood to discover that the
> tarps were as flimsy as cheese cloth and the wood
> was soaked. We moved it up
> against the kiln, then in front of the fire
> box.....hardest firing we ever
> had....but, the pots were full of surprises.
> My last firing the wood was dry, red oak.
> ....Easiest firing we've had
> as far as raising temp. We also split it into
> smaller sticks, which helped,
> I'm sure....but, the pots were very predictably
> pretty....no
> surprises.....I'm in for the surprises.
> Finding that happy medium would be like firing
> in the perfect world.
> Wood is one of the most challenging variables.
> Nils told me that during
> a recent firing of a "train kiln", they cut down a
> small pine tree (I think
> he said pine) and stoked it at the end of the three
> day firing. He said it
> gave wonderful reduction results. Every time we fire
> here, my trees start to
> shake in their roots.
> See you soon,
> Merrie
> Who sits down during a firing ?!? If we are not
> stoking, we are dancing !
> Well....maybe we sit for a spell......I just don't
> remember the sitting down
> time.
>
>
______________________________________________________________________________
> 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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