Talbott on sun 26 oct 97
Knowing very little about the chemical formation of crystals, I wonder why
most crystalline glazes are fired in oxidation. To my knowledge the
crystals develop during the "cool-down" cycle which is in oxidation anyway.
Why would it matter if one were to fire a crystalline glaze on the way up
in reduction and then just allow the cool-down cycle to remain in
oxidation. Your responses will be appreciated... Marshall
2nd ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1998)
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Karl P. Platt on thu 30 oct 97
Talbott wrote:
> ----------------------------Original message----------------------------
> Knowing very little about the chemical formation of crystals, I wonder why
> most crystalline glazes are fired in oxidation. To my knowledge the
> crystals develop during the "cool-down" cycle which is in oxidation anyway.
> Why would it matter if one were to fire a crystalline glaze on the way up
> in reduction and then just allow the cool-down cycle to remain in
> oxidation. Your responses will be appreciated... Marshall
>
>
Reduction only serves color development. Many crystalling glazes have been/are
made in electric kilns -- it's a lot easier with a groovin'1990's controler
DonKopy@aol.com on sat 1 nov 97
Hi everyone,
Marshall Talbott wrote:
8<---I wonder why most crystalline glazes are fired in oxidation.
To my knowledge the crystals develop during the "cool-down" cycle which is in
oxidation anyway. Why would it matter if one were to fire a crystalline glaze
on the way up in reduction and then just allow the cool-down cycle to remain
in oxidation. Your responses will be appreciated... --->8
The answer as I see it is that most crystalline glazes have on the order of
..6 - .8 moles of zinc. As I understand it zinc doesn't do well in reduction.
There have been reduction crystalline glazes produced. I did see a reference
in an old (circa 1960's or 70's ?) Ceramics Monthly. The author produced
reduction color shifts in the glazes by introducing cooking oil through the
peep hole of an electric kiln through a drip feed mechanism. I imagine you
could fire oxidation on the way up, cool down to 2012F, soak around 4 hours,
or slow cool from 2012-1700 over 4-6 hours and introduce a reduction
atmosphere after the crystals have been formed on the way down. There is a
lot of trial and error to get the right cycle. Small kilns with controllers
are much more suited for crystal growing than a manually controlled larger
gas kiln. Exacting control and logging is needed in order to get repeatable
results.
The last time I grew crystals I did get a few beauties out of the firing.
Most however had the problem of too many crystals, covering the platters
entirely. Some grew three dimentionally producing a very rough unpleasant
texture. I soaked at 2012 for 4 hours, then slow cooled to 1400 over another
4 hours. Man....did I get crystals. There are times when more isn't better.
Norton wrote a little bit about crystal development with some illustrative
pictures of how the soaking temperature (a rather narrow window) affected the
shape of the crystals. If you really want to know more, read the section on
crystallization in "Ceramic Glazes" by Parmalee (back in print and worth
every penny). Herbert Sanders wrote about crystals (but not as much technical
detail) in "Glazes for Special Effects" worth it if you can find it . "Glazes
for Special Effects" is long out of print.Try The Book Exchange [may have
changed their name to Ceramic Arts Library 1-800-323-6748] Corning NY)
I did write about the glaze composition in more detail about a year ago on
Clayart don't think the archives were capturing at that time though. I need
to get some work done so I have to sign off. If I have the time (very busy 6
weeks coming up) I'll dig up the other post.
Don't forget catch bowls for the glaze that will flow right off the pot.
Happy Crystals,
Don Kopyscinski
Rick Sherman on sun 2 nov 97
Marshall Talbott wrote:
8<---I wonder why most crystalline glazes are fired in oxidation.
To my knowledge the crystals develop during the "cool-down" cycle which
is in oxidation anyway. Why would it matter if one were to fire a
crystalline glaze on the way up in reduction and then just allow the
cool-down cycle to remain in oxidation. Your responses will be
appreciated... --->8
and Dan Kopyscinski says
....The answer as I see it is that most crystalline glazes have on the
order of .6 - .8 moles of zinc. As I understand it zinc doesn't do
well in reduction. There have been reduction crystalline glazes
produced. I did see a reference in an old (circa 1960's or 70's ?)
Ceramics Monthly. The author produced reduction color shifts in the
glazes by introducing cooking oil through the peep hole of an electric
kiln through a drip feed mechanism...
------------------------response--------------------------------------
Linda Brendler earned an MFA developing copper red crystals. She
worked with Herbert Sanders and Calton Ball on the thesis. I have a
pot with overlapping red crystals. As she continued experimenting, she
was producing red crystals on green and soft yellow/tan backgrounds.
She fired in an elecric kiln and I persume she used localized reduction
techniques.
RS
San Jose, CA
rballou@mnsinc.com on mon 3 nov 97
Marshall,
Marcia Silverman and I believe, John Tilton (who's been on the list, I
think) have done quite a bit of work with crystalline glazes fired in
reduction. I have several of Marica's pots. They are beautiful! The
crystals are much smaller and the glaze surface is matte. It's an entirely
different effect from the oxidation crystalline glazes.
If you're interested in pursuing reduction crystalline glazes, Ian Currie's
book has a section on them. There are many different types of crystalline
glazes besides the familiar zinc based ones. For example, the section on
pyroxene crystals mentions that they will crystallize out of copper reds
and temmokus (tea dust temmokus). It sounds like pyroxene crystals are easy
to get with a calcium glaze that has some magnesium and is low in alumina.
The proper firing cycle is necessary. Currie has more information,
including unity formulae.
Ruth Ballou
rballou@mnsinc.com
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