mel jacobson on fri 22 oct 04
i thought that was covered before.
sorry.
fire down is always, always, always oxidize.
no sense in having reduction.
you only want heat.
slow things down.
make your kiln into an old chinese hard brick, wood
fired kiln.
it is the time, time, time that it takes to cool.
remember, just because a kiln is fired with wood, and
smokes, it does not mean the chamber is under heavy reduction.
often just the opposite. smoke outside, means none inside.
(there are theories, and science here...no time for that today.)
ron and john have helped us all do that with
electric kilns. what happens when the kiln cools.
LOTS AND LOTS
learning.
what a concept.
and, try new things, don't get stuck in 1955.
it was not all good THEN, in fact a great deal of bs.
new ideas make us reach.
it is like the question. `how do i load an electric kiln?`
like we all say. depends. what kind of pots, what do you
want, what temp?????, it all changes. try different ways, chart
it...find your way. no easy answers.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
John Hesselberth on fri 22 oct 04
On Friday, October 22, 2004, at 11:03 AM, mel jacobson wrote:
> fire down is always, always, always oxidize.
>
> no sense in having reduction.
> you only want heat.
> slow things down.
To add to what Mel said, reduction is most effective before the glaze
seals over--that is the only way the reducing gases can 'reach into'
the glaze and do their thing. Reducing during cool down after the glaze
is fully melted probably wouldn't affect the glaze more than an atom or
two deep. I doubt it would even be enough to get a luster effect though
I could be wrong about that. Most of what can happen (or not) during
cooling is crystal formation and growth.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Vince Pitelka on fri 22 oct 04
> fire down is always, always, always oxidize.
But Mel, what about John Neely's wonderful pots, produced by reduction
cooling, in other words, firing down in a reduction atmosphere? Be careful
of words like "always."
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
johnrichmond@MAC.COM on sat 23 oct 04
If the glaze is a silicate, reducing down doesn't seem to be effective.
If it is not a silicate, reduction has a dramatic effect on the way
down, i.e., lusters.
On Oct 22, 2004, at 11:03 AM, mel jacobson wrote:
> i thought that was covered before.
> sorry.
>
> fire down is always, always, always oxidize.
>
> no sense in having reduction.
> you only want heat.
> slow things down.
> make your kiln into an old chinese hard brick, wood
> fired kiln.
> it is the time, time, time that it takes to cool.
> remember, just because a kiln is fired with wood, and
> smokes, it does not mean the chamber is under heavy reduction.
> often just the opposite. smoke outside, means none inside.
> (there are theories, and science here...no time for that today.)
>
> ron and john have helped us all do that with
> electric kilns. what happens when the kiln cools.
> LOTS AND LOTS
> learning.
> what a concept.
>
> and, try new things, don't get stuck in 1955.
> it was not all good THEN, in fact a great deal of bs.
> new ideas make us reach.
>
> it is like the question. `how do i load an electric kiln?`
> like we all say. depends. what kind of pots, what do you
> want, what temp?????, it all changes. try different ways, chart
> it...find your way. no easy answers.
> mel
> From:
> Minnetonka, Minnesota, U.S.A.
> web site: my.pclink.com/~melpots
> or try: http://www.pclink.com/melpots
> new/ http://www.rid-a-tick.com
>
> _______________________________________________________________________
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> melpots@pclink.com.
>
>
John Richmond
4043 South Waterbridge Circle
Port Orange, FL 32129-9616
(386) 760-4686
Earl Brunner on sat 23 oct 04
What do you mean "if the glaze is a silicate"? Silica is a primary ingredient in almost all glazes.
johnrichmond@MAC.COM wrote:If the glaze is a silicate, reducing down doesn't seem to be effective.
If it is not a silicate, reduction has a dramatic effect on the way
down, i.e., lusters.
Earl Brunner
e-mail: brunv53@yahoo.com
John Britt on sat 23 oct 04
John,
Down firing in reduction has a substancial effect! Also, a "glaze
reduction" period at the peak temperature has a great effect. As you say,
it only effects the surface layer but that is significant.
As I show in my book, you can oxidize a firing and then reduce at cone 9
for an hour which will have an effect on the glazes and the clay body! You
can turn a high iron clay body dark brown this way. Everyone thinks it
was fired in reduction. This is a great way to get a brown body without
the strength loss of black coring (or grey coring). (Notice the tiles
pictured on page 47.)
This firing cycle, which I call O2, is good for leopard spot kaki (page Pg
73 - 74), Oil spots (pg 75 -77), oribe and peach bloom can all be fired in
this way.
Reduction firing down can produce many many other interesting effects. I
would suggest you try it!
John Britt
www.johnbrittpottery.com
John Britt on sat 23 oct 04
Vince,
I am with you on that word "always"! It usually is an overstatement.
I often fire down in reduction. And "striking" is a form of down firing in
reduction.
John Britt
www.johnbrittpottery.com
Ivor and Olive Lewis on sat 23 oct 04
I wonder what the chemistry is here and if the thinking behind the
idea of firing down a reduced ceramic item in an oxidising atmosphere
is in conflict with other ways in which we rely on the action of a gas
to do things for us. Seems to show that gas does not diffuse through
molten or setting vitreous silicates. If it does it seems to
contradict the idea that gases can diffuse out of a vitrified body and
make bubbles and pinholes.
Perhaps it is another instance of ignorance being blissful.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
John K Dellow on sat 23 oct 04
mel jacobson wrote:
> i thought that was covered before.
> sorry.
>
> fire down is always, always, always oxidize.
>
Ok mel next question, do you have the damper completly open ?
I have done a couple of Hank fire downs this year keeping the oxy at .1 ,by dropping the pressure down about 20% and colseing the damer to give the .1 reading.
Good results , but my highest reading is .6 and my teacher Ray cavell says I should be going to .65 when useing white clay with shino.
John
John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/
Ivor and Olive Lewis on sun 24 oct 04
<ingredient in almost all glazes.>>
True Earl, true.
But some surface applications are short in silica and allow surface
exposure of other ingredients that do not dissolve into the silicate
melt. Typical of these are the high Copper oxide and metallic
Manganese oxide finishes.
Kingery et al (p 206) have interesting things to say about the surface
of a silicate glass and pure silica at the molecular level.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
mel jacobson on sun 24 oct 04
yes tony, it works, and hank will more than
likely tell us it has little to do with him. and in many
ways he is correct..but, he has re/invented a technique,
and given it to many of us (at least those that will trust and
listen)...with his unselfish attitude and
class. he is one smart boy.
i have repeatedly said that i cannot figure out
why the entire kiln, reduction too, evens out.
lots of theories, but the even kiln is really one
of the best things about hank's fire down technique.
one of my corners, that did not reduce well is cured.
loading the kiln warm, with a load of christmas pots.
it is really nice that the left-over chinese test pots
take rhodes 32 really well. (joke)
and, tony, it is wonderful to have your life changed again.
clayart works well.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
Vince Pitelka on sun 24 oct 04
> I am with you on that word "always"! It usually is an overstatement.
> I often fire down in reduction. And "striking" is a form of down firing in
> reduction.
I have to thank John Britt for his tact, but I must apologize for my own use
of the word "always" in a post about arches, and that was right after I
scolded Mel for using the word "always." I stand corrected and humbled.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Bruce Girrell on mon 25 oct 04
Ivor wrote:
> Seems to show that gas does not diffuse through
> molten or setting vitreous silicates. If it does it seems to
> contradict the idea that gases can diffuse out of a vitrified body and
> make bubbles and pinholes.
Good questions, as usual, Ivor.
I don't think that gas under pressure making its way to the surface of a
viscous semi-liquid is not operating on the same principle as gaseous
diffusion. In the case of gas bubbles I would think that we would be working
with pressure, surface tension, gravity, and perhaps a few other things. In
the case of diffusion, we would be working on a molecular level with
relative concentrations, electron/ion mobilities.
I'm not sure exactly how gases interact with semi-solids, but in the case of
boron, phosphorous, etc. diffusing into silicon, the diffusion constant is
very strongly temperature related:
D' = D(exp(-E/(kT))) = D/exp(E/(kT))
where:
D' = diffusion coefficient at temperature
D = diffusion coefficient at standard conditions
E = activation energy
k = Boltzman constant
T = temperature
The details of the equation are pretty much immaterial. For any given
element, D, E, and k will be constant. What is important is that T in the
denominator of the exponential. As the temperature drops, the diffusion
coefficient plummets. I wouldn't expect too much in the way of diffusion
effects at the soak and hold temperatures being discussed.
Bruce Girrell
in glorious sunny northern Michigan where we had a magnificent sunrise with
pink, lavender, peach, and blue colors and now we have bright sun shining on
trees of all manner of brilliant colors. Even the oaks are starting to get
with the program.
Hank Murrow on tue 26 oct 04
On Oct 24, 2004, at 11:53 AM, mel jacobson wrote:
> yes tony, it works, and hank will more than
> likely tell us it has little to do with him. and, tony, it is
> wonderful to have your life changed again.
> clayart works well.
Dear Mel;
I published the Soak idea in the September 2001 issue of Ceramics
Monthly, but the idea really took off from your trials and mention on
Clayart. I am continually impressed with the speed of dispersion within
our beloved Clayart........ for better or worse.
I'll take the better every time, the worst can take care of itself.
Cheers, Hank
www.murrow.biz/hank
Ivor and Olive Lewis on tue 26 oct 04
Dear Bruce Girrell,
I think some thing happened on the way to the Forum <that gas under pressure making its way to the surface of a viscous
semi-liquid is not operating on the same principle as gaseous
diffusion.>>
Did you mean "A gas under pressure making its way to the surface is
operating under a differing principle to gaseous diffusion" ? If so, I
agree with you !
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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