Hank Murrow on wed 15 aug 12
On Aug 15, 2012, at 7:51 PM, David Beumee wrote:
> I've been trying to learn how to fire my new soda kiln,
> and I have a question concerning charging the kiln
> at temperature with soda ash solution.
> In her book "Soda, Clay and Fire" Gail Nichols
> mentions closing the damper at the time of charging
> (spraying) the kiln at cone 8 - 10 when power burners
> are being used. Her point is to keep the solution in the kiln
> long enough for it to be effective.
> I'm firing with Ward burners, and they rip,
> and to close the damper seems like a recipe for disaster
> when they're on full.
> There are pilot burners attached to the mains
> so it would be easy to shut down the big dogs, charge the kiln, and =3D
relight.
> My question is this: How long does it take for soda ash solution
> to do its work at cone 10? Is the glaze formed instantly,
> or would it be an advantage to keep the steam solution in the kiln.
> I don't want to lose too much temperature.
When I fired the cross draft soda kiln at Appalachian Center for Craft, =3D
It got to cone 11 front, cone 7 lower back, and I turned the burners =3D
off, closed the damper, and sprayed the 2.5 gallon and 4#'s soda mixture =
=3D
around the interior of the kiln from several ports. I left it for ten =3D
long minutes like that, and then opened up the damper and turned on the =3D
burners half way for another ten before shutting it down and dampering.
The next day, we peeked, and the 12 was bending in front and 10 was down =
=3D
at the lower back: a nice fire! The things in front were more heavily =3D
glazed, but nearly all were saleable. Still using s few pieces from that =
=3D
fire to remind me. Thanks Vince!
Cheers, Hank=3D
Mark Cortright on wed 15 aug 12
What I can tell you is about salting as I fire a salt kiln for many
years now and the same is true with soda as you want the vapors to get
on the wares.
When up to temp-cone 8 and above we salt with liquid solution via
sprayers(spray ports) also toss in some soda tacos in burner ports.
when we spray it in we close down the damper -not closed but choked
in. We leave the burners alone. This vapor sits in kiln while we spray
in more salt and soda tacos-we watch the temp drop on a digital
pyrometer when it drops off a far amount we open damp back to original
setting and let it regain the climb . once above where we started a
bit we do it all over again -we repeat this till the rings we pull out
have what we are looking for on them and stop salting and close up the
kiln.
Hope this helps
Mark Cortright
www.liscomhillpottery.com
David Beumee on wed 15 aug 12
I've been trying to learn how to fire my new soda kiln,
and I have a question concerning charging the kiln
at temperature with soda ash solution.
In her book "Soda, Clay and Fire" Gail Nichols
mentions closing the damper at the time of charging
(spraying) the kiln at cone 8 - 10 when power burners
are being used. Her point is to keep the solution in the kiln
long enough for it to be effective.
I'm firing with Ward burners, and they rip,
and to close the damper seems like a recipe for disaster
when they're on full.
There are pilot burners attached to the mains
so it would be easy to shut down the big dogs, charge the kiln, and relight=
.
My question is this: How long does it take for soda ash solution
to do its work at cone 10? Is the glaze formed instantly,
or would it be an advantage to keep the steam solution in the kiln.
I don't want to lose too much temperature.
David Beumee
Lafayette, CO
ivor and olive lewis on thu 16 aug 12
Dear David Beumee,
A solution of Sodium Carbonate will pass through several stages before it
becomes integrated into the surface of you pots.
The first stage is evaporation of water. Once the solution enters the kiln
evaporation starts and will be terminate just above 100 deg C (212F). Your
Sodium Carbonate is now an anhydrous dust which is swept around in the kiln
atmosphere. If the Damper is not closed the dust will be swept out of the
kiln as waste effluent.
To retain particulate Sodium Carbonate in your kiln you need to reduce gas
flow so there is no blow back at the fire mouths when the damper is closed.
This may mean attaining a balance between a slightly open damper and a much
reduced gas flow to retain the maximum amount of Sodium Carbonate in the
kiln
Sodium carbonate melts at just below 900 deg C. If your cones are deforming
at 1200 degrees C or higher then the liquid mist of Sodium Carbonate which
settles on the clay minerals will dissolve the products of the breakdown of
clay and other minerals. You will have to rely on draw rings to judge the
progress of your firing.
As with traditional salting using Sodium Chloride, you rely on heat
retention in your refractories to stabilise the heat energy preventing your
kiln from cooling (governed by latent heats of evaporation and fusion and
Specific heats of the compounds involved) as you work through a series of
cycles of damping down, injection of more Soda solution. Reheating your kil=
n
gives time for essential chemistry to work as you advance the temperature t=
o
maturity heat..
Trusting that makes sense and satisfies you questions.
Regards,
Ivor Lewis,
REDHILL,
South Australia
Vince Pitelka on thu 16 aug 12
David Beumee wrote:
"I've been trying to learn how to fire my new soda kiln, and I have a
question concerning charging the kiln at temperature with soda ash solution=
.
In her book "Soda, Clay and Fire" Gail Nichols mentions closing the damper
at the time of charging (spraying) the kiln at cone 8 - 10 when power
burners are being used. Her point is to keep the solution in the kiln long
enough for it to be effective. I'm firing with Ward burners, and they rip,
and to close the damper seems like a recipe for disaster when they're on
full. There are pilot burners attached to the mains so it would be easy to
shut down the big dogs, charge the kiln, and relight. My question is this:
How long does it take for soda ash solution to do its work at cone 10? Is
the glaze formed instantly, or would it be an advantage to keep the steam
solution in the kiln. I don't want to lose too much temperature."
Hi David -
I wonder what Gail Nichols means by "effective?" Gail goes for very heavy
soda effects on her own work, while the reason many people choose soda over
salt is for a less invasive, less corrosive effect. The choice of whether
or not to close the damper depends on whether you want even overall soda
deposition or asymmetrical soda effects. I prefer the latter, and that is
one of the reasons I prefer crossdraft soda kilns - they give you more
choices. You can get very even overall soda deposition by closing the
damper when you charge and thus trapping the gasses in the kiln. I would
never shut down the burners, because you need them to provide turbulence. =
I
am not sure what you mean by "to close the damper seems like a recipe for
disaster when they (the power burners) are on full." What do you think is
going to happen? I expect that you are thinking about the backpressure at
the burner ports causing soda fumes to impact the burners. That is a
concern and you should watch them closely. If you need to turn the burners
down a little, fine, but don't shut them off, because you do need that
turbulence if you want fairly even overall soda deposition.
If you want more asymmetrical effects then leave the damper partially or
fully open. The soda fumes will still affect the wares but will be moving
through the kiln more quickly. Place the wares in the kiln with this in
mind. With the damper open, you will get much heavier soda deposition on
the side where the fumes hit the wares - the side facing the bagwall. And
obviously, you can have any variation between a wide-open damper for maximu=
m
asymmetrical effect, or a fully-closed damper for the most even overall
deposition.
We have charging ports in the front and back of the kiln above the firebox,
and that is the only place we spray soda the soda solution. We do not use
burritos, and we never spray soda directly onto the wares. For a cone-10
firing we generally charge the kiln as cone-10 is going down. We usually
mix three or four pounds of soda ash with two gallons of hot water and put
it in a garden sprayer, and we spray in fifteen-second bursts in the front
and the back charging ports, fanning the spray up and down the wall of the
kiln and across the firebox floor, never towards the bagwall. I just wait
until the atmosphere clears completely, which usually takes about five
minutes, and then I charge again. After charging the first two or three
times I pull a draw-ring top and bottom to gauge soda deposition. I
generally have five or six draw rings lined up inside spy holes near the to=
p
and bottom of the kiln, but I rarely have to pull more than two or three of
them before deciding that the firing is done. In my own firings, I generall=
y
use about half of the prepared soda solution, so I am actually only chargin=
g
about two pounds of soda ash.
You didn't ask about this, but one more consideration is how long you fire
after spraying the soda. For the best soda-fired effects I think it is
important to make sure that the kiln reaches maximum maturation temperature
after you spray your soda, just to make sure you achieve the most durable
surface. At the same time, if you spend very much time near or at
maturation temperature after you spray the soda, you are allowing a lot mor=
e
thermochemical action between glaze and body, and you are allowing the
sodium-silicate glaze to diffuse and smooth out. For some people that will
be a good thing, but if you want distinctively soda-fired effects, then
don't wait too long after the final charging before you shut down the kiln.
The draw-rings are the best indicators.
People often talk about the variation in salt-fired surfaces on historic
German wares, and so much of that had to do with how long the kiln is fired
after the final charging of salt. If there is a very distinct pebbly
surface, then the kiln was shut down soon after the final charging. If
there is more of a smooth overall glaze then the kiln was fired for a while
after the final charging.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net
http://iweb.tntech.edu/wpitelka/
Dan Hill on fri 17 aug 12
Hi David
Are you spraying in the soda solution mixed with water or using the Gail
Nichols approach?
My experience is with spraying a saturated soda/hotwater solution at ^6. I
turn the burners down slightly once ^6 is staring to soften and spray
through 4 ports around the kiln. I spray in 10 second bursts while rotating
around the kiln. The kiln only loses about 25 degrees celcius during the
process then I allow for the kiln to gain back the temp. Then I do that ove=
r
again. By that time ^7 is usually bending.
I usually turn down the gas pressure slightly and leave the damper as is
during the spraying. As Vince says is depends on the type of results you ar=
e
after.
Do you soda firers use soda ash or soda bicarb or a combination for your
firings.
I am wondering because I get some bubbling on pot edges and handles where
the soda build up is heavier. I use a mix of half soda ash and half soda
bicarb. Only happens on my stoneware body, not porcelain.
Dan Hill
Hill Pottery
www.hillpottery.com
> In her book "Soda, Clay and Fire" Gail Nichols
> mentions closing the damper at the time of charging
> (spraying) the kiln at cone 8 - 10 when power burners
> are being used. Her point is to keep the solution in the kiln
> long enough for it to be effective.
> I'm firing with Ward burners, and they rip,
> and to close the damper seems like a recipe for disaster
> when they're on full.
> There are pilot burners attached to the mains
> so it would be easy to shut down the big dogs, charge the kiln, and
> relight.
> My question is this: How long does it take for soda ash solution
> to do its work at cone 10? Is the glaze formed instantly,
> or would it be an advantage to keep the steam solution in the kiln.
> I don't want to lose too much temperature.
>
> David Beumee
> Lafayette, CO
ksavino@BUCKEYE-EXPRESS.COM on fri 17 aug 12
David, I can 't advise re: your burners, but I can tell you what I do with =
soda and a couple of venturis.
I have one burner in the right front of my medium-small cat and one in the =
left/rear. The goal is to get a "swirl" of heat and soda moving from bottom=
to top, and then back to bottom. I do close my damper to charge with soda =
(suspended in hot water, with a metal tipped orchard sprayer, since burrito=
s are hard on my bricks) -- and then I "stir" the swirling fumes by opening=
and closing my knife blade (kiln shelf) damper -- reversing the flow of th=
e fire tornado, up, then down, then up again. I get pretty even coverage an=
d few dry spots. I am finding that the more I fire my kiln and the more res=
idual soda does the job for me, the less I have to fuss over the details of=
how to charge. I also ate the farking pyrometer and use it less and less, =
watching color/cones instead. I 'm firing in the weekend after this one, =
hope for cool weather and no rain.
My biggest soda kiln problem so far has been the time I used old oat bran a=
s the combustible in my wadding. Between the time I loaded and the time I c=
ame back to fire, chipmunks had nibbled them apart, tipping pots and leavin=
g little poops all over my kiln shelves. Live and learn.
Yours
Kelly in Ohio -- home late from glaze night with my guild class -- last nig=
ht it was hosting the copper etching workshop at the community studio. Poor=
Jeff can hardly tell I 'm back from the North woods.
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