Craig Martell on mon 26 apr 04
May related the following:
> He went on to say, it's micro-crystal, that has nothing to do with cooling;
>Only large crystal - as in zinc silicate crystals requires slow cooling.
Hello May:
He's wrong. Slower passage through certain temp ranges has a great deal to
do with crystal formation no matter what the size of the crystal.
regards, Craig Martell Hopewell, Oregon
May Luk on mon 26 apr 04
Hi all;
The other day, I was in a conversation with some potters. Another potter is
starting to experiment with ash glaze in reduction. She was mentioning matte
effect. I know nothing about ash glaze nor reduction firing. I could only
relate ash glaze to stringing - found that word in the dictionary.
From my participation with clayart and my glaze studies, I managed to say:
"maybe controlled cooling?" Another very experienced potter, who is also a
ceramic tutor spoke with authority [a man potter!] saying, it has nothing to
do with the cooling, it has to do with blah blah [at this point, I blanked
out with what he said about "blah blah", because of his tone of voice.] He
went on to say, it's micro-crystal, that has nothing to do with cooling;
Only large crystal - as in zinc silicate crystals requires slow cooling.
What he said contradicts with what I've learnt. His macho tone of voice
ignited my inner fire cracker. I was compelled to go home and re-read MC6G
and Hamer dictionary Page 95.
What y'all reckon? Maybe what he said is true with ash glaze in reduction?
Thank your for your time
May
London, UK
Ivor and Olive Lewis on tue 27 apr 04
Dear May Luc,
Very rapid cooling is needed to produce a transparent glaze,
Slower cooling allows chemical reactions to take place in the melt
with those compounds which have the highest melting point (or if you
wish, top freezing point) being the first to crystallise. This will
take place randomly throughout the glaze and if cooling proceeds then
the glaze will go opaque with, firstly the substance with the highest
melting point , then the next one lower and so on until the glaze has
Devitrified. It can be both Opaque and Mat.
If cooling is very slow or prevented,and the glaze is not allowed to
reach the point at which a second material comes out of solution a new
phenomenon happens. The larger of the crystals start to enlarge at the
expense of material from smaller crystals. This is how Zinc crystals
become so big.
In glazes which are high in Calcium it is possible to get two types of
crystal. Dolomite glazes can produce two sets of crystal compounds
If this is not clear to you just ask for clarification.
Best regards,
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From: "May Luk"
To:
Sent: Monday, 26 April 2004 8:13
Subject: Ash glaze -Micro-crystal - Controlled cooling - fact check
please
> Hi all;
>
> The other day, I was in a conversation with some potters. Another
potter is
> starting to experiment with ash glaze in reduction. She was
mentioning matte
> effect. I know nothing about ash glaze nor reduction firing. I could
only
> relate ash glaze to stringing - found that word in the dictionary.
> From my participation with clayart and my glaze studies, I managed
to say:
> "maybe controlled cooling?" Another very experienced potter, who is
also a
> ceramic tutor spoke with authority [a man potter!] saying, it has
nothing to
> do with the cooling, it has to do with blah blah [at this point, I
blanked
> out with what he said about "blah blah", because of his tone of
voice.] He
> went on to say, it's micro-crystal, that has nothing to do with
cooling;
> Only large crystal - as in zinc silicate crystals requires slow
cooling.
>
> What he said contradicts with what I've learnt. His macho tone of
voice
> ignited my inner fire cracker. I was compelled to go home and
re-read MC6G
> and Hamer dictionary Page 95.
>
> What y'all reckon? Maybe what he said is true with ash glaze in
reduction?
>
> Thank your for your time
> May
> London, UK
>
>
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ASHPOTS@AOL.COM on tue 27 apr 04
when i fire my ashglazes i slow cool. It takes me 2 days to cool the Alpine..
When ive been in a rush and quick cool there is a differnece,, I like the
look of the slow cool..
The Alpine is full of Mudfire potters work in the kiln now , being slow
cooled.Camping on the BLUFF worked out fine
Mark
John Hesselberth on tue 27 apr 04
On Monday, April 26, 2004, at 06:43 AM, May Luk wrote:
> From my participation with clayart and my glaze studies, I managed to
> say:
> "maybe controlled cooling?" Another very experienced potter, who is
> also a
> ceramic tutor spoke with authority [a man potter!] saying, it has
> nothing to
> do with the cooling, it has to do with blah blah [at this point, I
> blanked
> out with what he said about "blah blah", because of his tone of
> voice.] He
> went on to say, it's micro-crystal, that has nothing to do with
> cooling;
> Only large crystal - as in zinc silicate crystals requires slow
> cooling.
Hi May,
The only way this potter could be correct is if he has formulated a
glaze that doesn't completely melt during firing. Then cooling rate
might have little, if any, affect on crystal size and growth (but even
then it would depend on the specific composition)--they would just be
unmelted particles--and you probably know my opinion of glazes
formulated that way.
However if the glaze is thoroughly melted during firing then Craig
Martell's answer is the correct one and your friend is wrong.
Regards,
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on tue 27 apr 04
Hi May,
The great majority of potters did not understand the importance of cooling
- that is changing now - he simply does not know what he is talking about.
You are going to run into this often - there is no shortage of teachers who
stopped learning - probably as soon as they got their jobs.
The trick - for them - is to sound like they know what whey are talking
about - that way few question what they say.
RR
>Hi all;
>The other day, I was in a conversation with some potters. Another potter is
>starting to experiment with ash glaze in reduction. She was mentioning matte
>effect. I know nothing about ash glaze nor reduction firing. I could only
>relate ash glaze to stringing - found that word in the dictionary.
>From my participation with clayart and my glaze studies, I managed to say:
>"maybe controlled cooling?" Another very experienced potter, who is also a
>ceramic tutor spoke with authority [a man potter!] saying, it has nothing to
>do with the cooling, it has to do with blah blah [at this point, I blanked
>out with what he said about "blah blah", because of his tone of voice.] He
>went on to say, it's micro-crystal, that has nothing to do with cooling;
>Only large crystal - as in zinc silicate crystals requires slow cooling.
>
>What he said contradicts with what I've learnt. His macho tone of voice
>ignited my inner fire cracker. I was compelled to go home and re-read MC6G
>and Hamer dictionary Page 95.
>
>What y'all reckon? Maybe what he said is true with ash glaze in reduction?
>
>Thank your for your time
>May
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Lee Love on wed 28 apr 04
Ron Roy wrote:
>The great majority of potters did not understand the importance of cooling
>- that is changing now - he simply does not know what he is talking about.
>
>
Yes, this is a problem modern technology has brought us, as we
find in our modern softbrick electric kilns. In large, traditional
woodkilns, it may take the kiln over a week to cool.
>The trick - for them - is to sound like they know what whey are talking
>about - that way few question what they say.
>
You got that right! Beware of teachers who think everyone
else is wrong and only they have "the one true way." Eschew Gurus
and look for real teachers. One good test of a true teacher is that he
has the humility to learn from his students.
--
Lee in Mashiko, Japan http://mashiko.org
May Luk on wed 28 apr 04
Hiya;
Thank you all for your valuable input. I learnt more by asking questions and
being curious.
There are many adminstrative duties and bureaucractic BS for teachers in
colleges. Some stop learning and some can't even find time to make pots.
They are just trying to make a living. Everything comes from the top though:
Pity the students, swimming in mystery and confusion. Luckily, not all
teachers are like that.
Ivor;
May I impose. Can you please clarify :
"In glazes which are high in Calcium it is possible to get two types of
crystal. Dolomite glazes can produce two sets of crystal compounds"
And if you don't mind me giving it a go:
1.a-High Calcium + Low alumina glaze > matte thru the formation of calcium
silicate crystals.
1.b-In iron glaze, calcia might form yellow crystalline compounds with the
Fe2O3 producing a 'lime matte.' Thus, the other type of crystal?
2-Dolomite matt: formation of calcium silicate crystals and magnesium
silicates?
My sources: Hamer's dictionary, digitalfire.com-, ceramicweb at SDSU.edu
Thanks a million
May
Becoming a glaze geek
Dave Finkelnburg on wed 28 apr 04
May,
I suspect your tutor was attempting to say the micro-crystalline
surface on an ash glaze cannot be achieved unless the glaze has an excess of
flux to begin with. Without that composition slow cooling will do nothing
for the glaze.
The excess of flux, usually calcium, is typical of a wood ash glaze.
Cool the glaze fast and it will likely come out glossy, but cool it
slowly or fire down so as to hold the kiln between 1,750 and 1,950F for 3
hours and the same glaze will produce lovely satin to matt surfaces on the
thick rivulets of the glaze. Some kilns, as Earl Brunner pointed out, cool
slowly enough that they naturally produce a matt surface with such a glaze.
Others take the fire down approach.
Good glazing,
Dave Finkelnburg
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