mel jacobson on wed 8 jun 05
i have been following hank's method of down firing
for 5 years. every firing...reduction or oxy.
the saturated iron pots for the `iron saga` where all
fired oxy, then i re lit the kiln at 1900f and fired
between 2-5 hours. one burner, oxy strong cone 11-13.
the crystal growth was amazing...and of course
we got many new colors. gold being one.
i do believe that the base color or quality of the iron
that we used was clearly affecting the color of the glaze.
iron was not iron. each one created a new look or color.
we used at least 8 different iron combinations.
we did NOT use rutile. ever.
i was convinced that we would get hare's fur if we used
rutile...but we can find no evidence that the chinese a thousand
years ago were mining rutile. it was iron oxide, black, brown, red and
yellow. (of course that is a guess, we were not around and no
one wrote a cm article about it.)
as nils and me discussed last night. so much is about instinct,
experience, and observation.
i do not do complex chemistry...but i have fired thousands of kilns full,
in many places...i do understand fire and glaze. in many ways, it
is more important to me than the chemistry. and the results speak
for themselves. joe knows the chemistry, but he did not glaze, mix,
layer or fire my kiln...i did. and he trusted me to be free, organize
my own way, and proceed as a potter...not a chemist. that was
his territory. the combination of potter/chemist is the recipe for
success. so many want a chart, a graph....something from a gas
company...`how many btu's do i actually need?` well not nearly
what you think. how much reduction? not nearly as much as many
give the pots. same for shino and red. iron red in particular.
light reduction works. timing that reduction is what makes the
pots great. the in and out of reduction of a wood kiln is nice...yes
it is wonderful. but i would prefer i constant, light reduction for the
entire firing. know what it looks like when firing...this black smoke,
long licking flame does not make great pots in my opinion. i think that
is what destroys the great shino. that is why the re/fire in an electric
kiln brings out the magic. the crusty crap on the surface is burned off.
again...my guess.
mel
from mel/minnetonka.mn.usa
website: http://www.pclink.com/melpots
Hank Murrow on wed 8 jun 05
On Jun 8, 2005, at 3:37 PM, mel jacobson wrote:
> i have been following hank's method of down firing
> for 5 years. every firing...reduction or oxy.
>
> the saturated iron pots for the `iron saga` where all
> fired oxy, then i re lit the kiln at 1900f and fired
> between 2-5 hours. one burner, oxy strong cone 11-13.
>
> the crystal growth was amazing...and of course
> we got many new colors. gold being one.
Dear Mel;
I understand your experience with saturated iron glazes, and suggest
the reduction is necessary for the very low iron shinos. I think the
iron needs to get stirred into solution by early reduction, then
re-oxidized.
> ..this black smoke,
> long licking flame does not make great pots in my opinion. i think
> that
> is what destroys the great shino. that is why the re/fire in an
> electric
> kiln brings out the magic. the crusty crap on the surface is burned
> off.
> again...my guess.
That might be the case. Someone with a smaller kiln should try these
alternative fires and demonstrate.
Cheers, Hank
www.murrow.biz/hank
Craig Martell on thu 9 jun 05
Hank made this comment to mel:
>I understand your experience with saturated iron glazes, and suggest
>the reduction is necessary for the very low iron shinos. I think the
>iron needs to get stirred into solution by early reduction, then
>re-oxidized.
Hello Hank and the rest of you folks with an interest in how shinos may work:
The above is something that totally eluded me. ie. I didn't consider this
or even think about it. It's important to consider the effect of reduction
and oxidation on iron in regard to it being a flux in reduction and not in
oxidation. Your observation about these small amounts needing the
reduction to become more active in the glaze is a very important point to
consider. Thanks for waking me up. This may very well be the key to
understanding why these glazes need to be reduced prior to a healthy
reoxidation for redder color.
regards, Craig Martell Hopewell, Oregon
John Hesselberth on fri 10 jun 05
On Thursday, June 9, 2005, at 02:06 PM, Craig Martell wrote:
> Your observation about these small amounts needing the
> reduction to become more active in the glaze is a very important point
> to
> consider. Thanks for waking me up. This may very well be the key to
> understanding why these glazes need to be reduced prior to a healthy
> reoxidation for redder color.
Craig, Hank, Liz, Mel and others,
I feel the urge to say this in my own words (and speculate a bit) to be
sure I understand what you are suggesting.
Iron that is present as impurities in ingredients is most likely in its
fully oxidized state. It is also widely dispersed. If you fire in an
oxidizing atmosphere that iron does not enter the melt (primarily
because of the high alumina levels) and stays widely dispersed. Its
color is effectively masked by all the white stuff because it is widely
dispersed as very tiny particles.
On the other hand in a reducing atmosphere the iron enters the melt and
serves as a flux. It may (and here is where I have the urge to
speculate) concentrate to some extent either because it becomes more
mobile in the melt and/or because all of it enters the melt and not all
of the alumina enters it. In any case it is somehow then in a physical
state where on reoxidation it is better able to crystallize out in
large enough crystals to show its color. Is that a reasonable
restatement of your thinking?
If that is what is happening it is absolutely fascinating.
Regards,
John
Hank Murrow on fri 10 jun 05
On Jun 10, 2005, at 10:01 AM, John Hesselberth wrote in part:
>
> Craig, Hank, Liz, Mel and others,
>
> Iron that is present as impurities in ingredients is most likely in its
> fully oxidized state. It is also widely dispersed. If you fire in an
> oxidizing atmosphere that iron does not enter the melt (primarily
> because of the high alumina levels) and stays widely dispersed. Its
> color is effectively masked by all the white stuff because it is widely
> dispersed as very tiny particles.
Hank agrees with this statement.
>
> On the other hand in a reducing atmosphere the iron enters the melt and
> serves as a flux. It may (and here is where I have the urge to
> speculate) concentrate to some extent either because it becomes more
> mobile in the melt and/or because all of it enters the melt and not all
> of the alumina enters it.
Here is where the Electron microscopy and Microprobe analysis suggests
strongly that there is no concentration anywhere in my Shino, so I find
the evidence does not support your working theory.
> In any case it is somehow then in a physical
> state where on reoxidation it is better able to crystallize out in
> large enough crystals to show its color.
NOW you have stated what I believe to be the case. The iron enters into
the Alumina/Silicate melt as a flux, and is now(thanks to the high
Alumina) able to form a lightly ferrous surface, which is then
available for re-oxidation during cooling, whether induced by firing
so, or just slow cooled in a thick hardbrick kiln.
> If that is what is happening it is absolutely fascinating.
Been fascinating me for 37 years!
Cheers, Hank
www.murrow.biz/hank
John Hesselberth on fri 10 jun 05
On Friday, June 10, 2005, at 02:58 PM, Hank Murrow wrote:
> Here is where the Electron microscopy and Microprobe analysis suggests
> strongly that there is no concentration anywhere in my Shino, so I find
> the evidence does not support your working theory.
Hi Hank,
I didn't say well what was going through my mind. I didn't mean a
concentration gradient through the the thickness. But somehow that iron
must rearrange itself (I'm visualizing something that might look like a
flocculated clay vs. a deflocculated one) so it can crystallize out in
larger (and therefore more visible) crystals.
John
Hank Murrow on fri 10 jun 05
On Jun 10, 2005, at 1:27 PM, John Hesselberth wrote:
> Hi Hank,
>
> I didn't say well what was going through my mind. I didn't mean a
> concentration gradient through the the thickness. But somehow that iron
> must rearrange itself (I'm visualizing something that might look like a
> flocculated clay vs. a deflocculated one) so it can crystallize out in
> larger (and therefore more visible) crystals.
I think the iron participates in the melt after reduction, instead of
being a passive component, and only then is it available for
re-oxidation. Somebody ought to write this up. Or, is that what we are,
by Clayart Consensus, already doing?
Had Tea in one of my white shino bowls today, all crawly and beaded up
with red iron color along the edges of the crawl.......... no wonder I
fell in love with that Momoyama bowl I held way back in '69! One has to
see the green tea dregs down in those pits to understand. At least I
can finally DO it, instead of merely drooling at the originals.
Cheers, Hank
www.murrow.biz/hank
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