mel jacobson on wed 5 sep 01
ron, would you please give us all a bit
of your wisdom on firing temmoku.
ian and i have been talking about it, and
with my new firing system ala hank, long
1900 soak, i imagine my temmoku will
crystallize.
i am thinking that a well reduced firing to cone 10,
and a quick cool, then not soak.
bright black and rust.
hmm.
what do you think.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: http://www.pclink.com/melpots
Ron Roy on fri 7 sep 01
My firings were long at the end - new kiln now and I expect some changes -
faster.
There will be no crystalization during a soak - fast cooling is best for
shiny glazes - super cooled liquids (shiny glazes) rely on the glaze
cooling quickly enough so they don't devitrify (crystalize.)
Depends on the glaze if it needs a soak - I think most kilns slow enough at
the end to work well with my tenmoku - it is on the fluid side. Others may
need a longer soak to help the gold to break enough - depends on the
fluidity.
Some tenmokus will work both ways I suppose - you will find out how yours
is best - try em top middle and bottom - with a cone beside them - you will
then know much more what is needed.
Had good luck refiring it - but the third time it runs too much.
I started to get crystals - which I did not like so started crash cooling
for an hour - burners off, damper open 2nd air open and spys open. I do not
have any mattes so I don't know what would have happened to them - depends
on the glaze I guess. I suspect some mattes will be more shiney.
Keep in mind - the top of your kiln may cool slower - best place for mattes
- bottom may cool faster - best place for shiney.
RR
>ron, would you please give us all a bit
>of your wisdom on firing temmoku.
>
>ian and i have been talking about it, and
>with my new firing system ala hank, long
>1900 soak, i imagine my temmoku will
>crystallize.
>
>i am thinking that a well reduced firing to cone 10,
>and a quick cool, then not soak.
>bright black and rust.
>hmm.
>what do you think.
>mel
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
Paul Taylor on wed 12 sep 01
Dear Mel
Your letter was addressed to Ron. Since others have commented I would
like to as well . a lot of us have been discussing this clayart for a long
time. The process is called devitrification and can be found in frank and
Janet hammers dictionary. I suppose Hank has a deserved reputation any help
he has given me has always been diffinitive and I doubt if he would claim
sole discovery for any thing .
Devitrification is an old technique and is a prerequisite for some glazes
there is a myth that the ancient chinese quoted as a source for this
information fast cooled their kilns. I gave some arguments that this is
relative to their kilns and left it at that.
Ron Roy's black will "probably" go a mat crystalline like cast iron. I
made up a black to Ron's formula. (we have similar materials but not exactly
the same) .
Devitrifying on an equivalent two day cooling cycle, which held the
crystallization point at a temperature around 1900 f, the glaze went mat
like a mat black snow - without the sparkle. Modern glazes are designed to
fire in modern kilns which most of us have. They are efficient glazes that
suit all. However they do not lend themselves to a long devitrification they
are not designed to. That is one of their essences - they are not dependent
on devitrificaton for their effects therefor they are more reliable.
Devitrificatuion is why other peoples glazes so often do not work in other
kilns. which again shows the cleverness of factory prepared glazes but the
rub is that they do not respond well or at all to devitrification they are
designed not to.
Note that if you have a glaze that forms too pure a glass you can
devitrify until the cows come home nothing will happen so fast cooling to
the temperature of crystal forming makes little difference to the surface .
If fast cooling was indulged in it is to manage the devitrification
process.
The devitrification only works if there are nuclei in the glaze to
crystallize They can be un dissolved silica or any undissolved matter
including I suspect some chemicals that are very sensitive to
devitrification form nuclei on cooling but I am not sure about that. some
glaze only work if there is a controlled devitrification cycle. Most glazes
can bee supercooled to about 2000 F or more because that sets the color
while others need a slow cooling for the glaze to heal properly.
ivor has suggested that the sintering and melting points of a gaze give an
indication as to the crustal forming temperature and his suggestion of
studying phase diagrams would save a lot of work if one was looking for the
most likely temperatures. I find them very difficult to follow. I suspect if
I made glazes for a living I would be more fluent.
Hanks suggestion for a temperature is a very good one for shinos and
celadons and I suspect the chinese did fast cool their kilns to this
temperature maybe with water then let the kiln slowly cool until by
experience they found they could pore water in again to halt the process or
to get the stuff out quicker or just let the kiln cool naturally till it
could be handled.
traditionally Temocue recipes behave similarly with very differing
materials and analyses. what creates the nuances in the glaze is the cooling
cycle - tea dust is a devitrifyed traditional temocu.
Also 1900 f is only the magic number for some glazes other glazes prefer
other temperatures for effects and longer or shorter devitrification.
what holds us up on all I have said is that you can put 1000 tests in a
kiln but only do one test kiln firing at a time so progress is so slow on
experimenting most of us can not afford to bother and stick to modern
approaches to glazing.
Regards Paul Taylor
If you have a good name your failings will always be blamed on others.
> From: mel jacobson
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 5 Sep 2001 22:22:37 -0500
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: ron roy/black
>
> ron, would you please give us all a bit
> of your wisdom on firing temmoku.
>
> ian and i have been talking about it, and
> with my new firing system ala hank, long
> 1900 soak, i imagine my temmoku will
> crystallize.
>
> i am thinking that a well reduced firing to cone 10,
> and a quick cool, then not soak.
> bright black and rust.
> hmm.
> what do you think.
> mel
>
> From:
> Minnetonka, Minnesota, U.S.A.
> web site: http://www.pclink.com/melpots
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
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> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
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