Talbott on sun 8 dec 96
Just curious to know how much time it takes you to glaze-fire up to
cone 10 in reduction..(the pottery has already been bisqued fired)...when
you are after good copper reds...?
This is my firing routine... Starting with a cold kiln -- I oxidize
to cone 010, about 900 celsius,..from then on I fire in reduction (oxy
probe around .62 or so) up to cone 10.. then I go into oxidation for 20
minutes, then I shut down and close everything up tight... What kind of
firing times usually gives you the best results when firing to get
strawberry reds??? Thanks...
.....Marshall.... ...PS.. I did get receive a few more applications and
inquiries over the past several days for the Gallery.. Please let me know
if you are interested...
Celia & Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
Bob Hanlin on mon 9 dec 96
Marshall:
I fire to c012 in OX and then reduce heavily until c1 drops. After that I
begin to open the damper bit by bit. I'm in a moderate reduction when c9
goes down. Then I clear to pure oxidation and hold that until c10 is over
and then I shut the bugger off. This works for me.
>----------------------------Original message----------------------------
> Just curious to know how much time it takes you to glaze-fire up to
>cone 10 in reduction..(the pottery has already been bisqued fired)...when
>you are after good copper reds...?
>
> This is my firing routine... Starting with a cold kiln -- I oxidize
>to cone 010, about 900 celsius,..from then on I fire in reduction (oxy
>probe around .62 or so) up to cone 10.. then I go into oxidation for 20
>minutes, then I shut down and close everything up tight... What kind of
>firing times usually gives you the best results when firing to get
>strawberry reds??? Thanks...
>
>....Marshall.... ...PS.. I did get receive a few more applications and
>inquiries over the past several days for the Gallery.. Please let me know
>if you are interested...
>
>Celia & Marshall Talbott
>Pottery By Celia
>Route 114
>P.O. Box 4116
>Naples, Maine 04055-4116
>(207)693-6100 voice and fax
>clupus@ime.net
>
>
Bob Hanlin
Oklahoma City
e-mail bhanlin@ionet.net
"Rafael Molina-Rodriguez (Rafael Molina-Rodriguez)" on tue 17 dec 96
Marshall :
I fire in an Alpine 24 cu. ft. to ^ 11 in 13 hours.
Your firing cycle sounds fine. I'm a little dubious of the oxidation at the
end of the firing. I just turn off the burners, gas and immediately close
the dampers and ports as soon as I reach temperature and the glazes
are fine.
I've heard people say that they're brighter if you oxidize but I'm skeptical.
I believe when you turn off the gas there's no combustion so there can't
possibly be reduction, hence, an oxidizing atmosphere. So why oxidize
at the end?
I let the kiln cool for 48 hours before I unload. Two questions for the
group here. If a glaze is going to craze does it matter how slow you cool
kiln before unloading? Does the slow cool, in effect, anneal the material
and the work is stronger because of this?
I submitted a couple of red glazes and a purple glaze a couple of weeks
ago. These are the class glazes we use. They work fine with the firing
cycle I employ.
One suggestion for applying copper reds and purples is to glaze inside
one day and outside the next or vice versa. These glazes have a nasty
habit of just falling off of pots during firing if you just submerge the pot in
glaze all at once. I feel if you glaze interior then exterior the glaze has a
better chance to soak into the porous bisque clay and adhere better.
BTW, in my experience one can achieve reds when firing a whole load
together or when reds are placed throughout the chamber along with
other glazes. The other glazes don't seem to affect the development of
color in copper reds. In my experience, quite the opposite takes place.
The copper that volatilizes travels around the chamber and does
interesting things to other glazes. Recently, the copper has ended up
coloring a wood ash base that is normally green (no colorants, but, base
does have Alberta Slip, hence, green color) but with specks of red from
copper. Very interesting.
Good luck!
Rafael
rmr3431@dcccd.edu
>>> Talbott 12/08/96 09:13pm >>>
----------------------------Original message----------------------------
Just curious to know how much time it takes you to glaze-fire up to
cone 10 in reduction..(the pottery has already been bisqued
fired)...when
you are after good copper reds...?
This is my firing routine... Starting with a cold kiln -- I oxidize
to cone 010, about 900 celsius,..from then on I fire in reduction (oxy
probe around .62 or so) up to cone 10.. then I go into oxidation for 20
minutes, then I shut down and close everything up tight... What kind of
firing times usually gives you the best results when firing to get
strawberry reds??? Thanks...
.....Marshall.... ...PS.. I did get receive a few more applications and
inquiries over the past several days for the Gallery.. Please let me know
if you are interested...
Celia & Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
Ron Roy on wed 18 dec 96
>I let the kiln cool for 48 hours before I unload. Two questions for the
>group here. If a glaze is going to craze does it matter how slow you cool
>kiln before unloading? Does the slow cool, in effect, anneal the material
>and the work is stronger because of this?
Hi Rafael,
The short answer is no. You may be able to stop the crazing at that point
but it will happen later. Try putting that combination in the freezer
(continuing the cooling.)
Cooling fast will cause the outside layer (the glaze) to contract faster
than the inside (clay) and thus precipitate crazing. In fact it is probably
true that you can induce crazing in some glazes which might not otherwise
craze by super fast cooling.
The question implies that the basic coefficient of expansion and
contraction between the clay and glaze can be changed by cooling slow at
lower temperatures - not so - it can only delay the inevitable.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Talbott on wed 18 dec 96
Rafael
I do oxidize at the end of the cycle because my glazes are much
brighter now because of this practice. And yes I do lose some red to blue
and green but overall the beauty and value of the pots are much better now.
If you have a red dull piece it has little attraction (at least to me and
my customers).. The oxidation at the end really gives me an overall
improvement in the vitreous appearance of my pots...Thanks for the
information .... Marshall
>----------------------------Original message----------------------------
>Marshall :
>
>I fire in an Alpine 24 cu. ft. to ^ 11 in 13 hours.
>
>Your firing cycle sounds fine. I'm a little dubious of the oxidation at the
>end of the firing. I just turn off the burners, gas and immediately close
>the dampers and ports as soon as I reach temperature and the glazes
>are fine.
>
>I've heard people say that they're brighter if you oxidize but I'm skeptical.
>I believe when you turn off the gas there's no combustion so there can't
>possibly be reduction, hence, an oxidizing atmosphere. So why oxidize
>at the end?
>
>I let the kiln cool for 48 hours before I unload. Two questions for the
>group here. If a glaze is going to craze does it matter how slow you cool
>kiln before unloading? Does the slow cool, in effect, anneal the material
>and the work is stronger because of this?
>
>I submitted a couple of red glazes and a purple glaze a couple of weeks
>ago. These are the class glazes we use. They work fine with the firing
>cycle I employ.
>
>One suggestion for applying copper reds and purples is to glaze inside
>one day and outside the next or vice versa. These glazes have a nasty
>habit of just falling off of pots during firing if you just submerge the pot in
>glaze all at once. I feel if you glaze interior then exterior the glaze has a
>better chance to soak into the porous bisque clay and adhere better.
>
>BTW, in my experience one can achieve reds when firing a whole load
>together or when reds are placed throughout the chamber along with
>other glazes. The other glazes don't seem to affect the development of
>color in copper reds. In my experience, quite the opposite takes place.
>The copper that volatilizes travels around the chamber and does
>interesting things to other glazes. Recently, the copper has ended up
>coloring a wood ash base that is normally green (no colorants, but, base
>does have Alberta Slip, hence, green color) but with specks of red from
>copper. Very interesting.
>
>Good luck!
>
>Rafael
>rmr3431@dcccd.edu
>
>>>> Talbott 12/08/96 09:13pm >>>
>----------------------------Original message----------------------------
> Just curious to know how much time it takes you to glaze-fire up to
>cone 10 in reduction..(the pottery has already been bisqued
>fired)...when
>you are after good copper reds...?
>
> This is my firing routine... Starting with a cold kiln -- I oxidize
>to cone 010, about 900 celsius,..from then on I fire in reduction (oxy
>probe around .62 or so) up to cone 10.. then I go into oxidation for 20
>minutes, then I shut down and close everything up tight... What kind of
>firing times usually gives you the best results when firing to get
>strawberry reds??? Thanks...
>
>....Marshall.... ...PS.. I did get receive a few more applications and
>inquiries over the past several days for the Gallery.. Please let me know
>if you are interested...
>
>Celia & Marshall Talbott
>Pottery By Celia
>Route 114
>P.O. Box 4116
>Naples, Maine 04055-4116
>(207)693-6100 voice and fax
>clupus@ime.net
Celia & Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
SANTERRE ROBERT on thu 19 dec 96
----------------------------Original message----------------------------
>Hi Rafael,
>The short answer is no. You may be able to stop the crazing at that point
>but it will happen later. Try putting that combination in the freezer
>(continuing the cooling.)
>Cooling fast will cause the outside layer (the glaze) to contract faster
>than the inside (clay) and thus precipitate crazing. In fact it is probably
>true that you can induce crazing in some glazes which might not otherwise
>craze by super fast cooling.
>The question implies that the basic coefficient of expansion and
>contraction between the clay and glaze can be changed by cooling slow at
>lower temperatures - not so - it can only delay the inevitable.
>Ron Roy
>Toronto, Canada
>Evenings, call 416 439 2621
>Fax, 416 438 7849
/////////////////////// Comment ////////////////////////////////////////
I've been silently following this glaze crazing/cracking,
expansion/contraction, glaze "fit" topic hoping to pull out some common
threads of "truth" to expand my very limited knowledge of ceramic chemistry
and physics. The "truths" I've been looking for are a smallish set of rules
I can refer to when thinking about formulating or modifying a glaze. Ron Roy's
comments above struck home with one clear truth - once the glaze is on the pot
your ability to influence the process is extremely limited. Firing is the
final step in bringing the process to completion and realizing the result, but
there are essentially no controllable variables at that point. The "fit" of
the glaze and clay body was determined when they were formulated.
My perhaps naive distillation of some of this discussion is that heating causes
things to expand and then they contract upon cooling. It's clearly more
complex then that when thinking about clay because I see a bisqued pot
SHRINKING, perhaps 10% in linear dimension after firing to ^10. So clearly
there are chemical/structural changes occuring that cause the clay body to
actually shrink and become more dense. Different clay bodies have different
percentages of shrink. Generally manufacturers tell me what percent shrinkage
to expect for their clay body or I can fire a sample and calculate shrinkage
myself - simple, my kind of "truth".
Ok, here's my beef. Why can't some similar, simple "truth" be known for
glazes. Isn't there some way to predict/calculate (based on formula) the
"shrink factor" for a particular glaze and then all I have to do is match
shrink factors for my glaze and my clay body and I'm home free? I suppose
there could be differences in the temperature and/or rate at which
shrinkage occurs which could still lead to crazing even though the endpoint
shrinkage fastors were matched, but one would think even that could be
empirically tested/or predicted and factored into considerations of glaze and
clay body fit. Isn't it possible to calculate percent shrinkage for glazes?
Why don't manufactures do this? Is there software - like Insight - that can
do this?
In my naivete I've probably reduced the problem to some ridiculous
impossibility and I anticipate I'll be pummelled to dust by some of you ceramic
engineers, but think about my challenge. Is this problem sooooo complex that
it can't be reduced to some fairly simple rules that a non-chemist/non-engineer
dummy like me can follow and get it right, say 80% of the time?
I'm hunkered down in my bunker now waiting for the "incoming".
Bob
santerre_robert@lilly.com
Bob Hanlin on fri 20 dec 96
>----------------------------Original message----------------------------
>I've heard people say that they're brighter if you oxidize but I'm skeptical.
>I believe when you turn off the gas there's no combustion so there can't
>possibly be reduction, hence, an oxidizing atmosphere. So why oxidize
>at the end?
It saves gas and the reds are at least as good!
BTW, in my experience one can achieve reds when firing a whole load
>together or when reds are placed throughout the chamber along with
>other glazes. The other glazes don't seem to affect the development of
>color in copper reds. In my experience, quite the opposite takes place.
>The copper that volatilizes travels around the chamber and does
>interesting things to other glazes. Recently, the copper has ended up
>coloring a wood ash base that is normally green (no colorants, but, base
>does have Alberta Slip, hence, green color) but with specks of red from
>copper. Very interesting.
>
>Good luck!
>
>Rafael
>rmr3431@dcccd.edu
>
>>>> Talbott 12/08/96 09:13pm >>>
>----------------------------Original message----------------------------
> Just curious to know how much time it takes you to glaze-fire up to
>cone 10 in reduction..(the pottery has already been bisqued
>fired)...when
>you are after good copper reds...?
>
> This is my firing routine... Starting with a cold kiln -- I oxidize
>to cone 010, about 900 celsius,..from then on I fire in reduction (oxy
>probe around .62 or so) up to cone 10.. then I go into oxidation for 20
>minutes, then I shut down and close everything up tight... What kind of
>firing times usually gives you the best results when firing to get
>strawberry reds??? Thanks...
>
>....Marshall.... ...PS.. I did get receive a few more applications and
>inquiries over the past several days for the Gallery.. Please let me know
>if you are interested...
>
>Celia & Marshall Talbott
>Pottery By Celia
>Route 114
>P.O. Box 4116
>Naples, Maine 04055-4116
>(207)693-6100 voice and fax
>clupus@ime.net
>
>
Bob Hanlin
Oklahoma City
e-mail bhanlin@ionet.net
Craig Martell on fri 20 dec 96
In a message dated 96-12-19 09:04:17 EST, Bob wrote;
<< Ok, here's my beef. Why can't some similar, simple "truth" be known for
glazes. Isn't there some way to predict/calculate (based on formula) the
"shrink factor" for a particular glaze and then all I have to do is match
shrink factors for my glaze and my clay body and I'm home free >>
First of all Bob, your post was full of good questions and nobody,
credentials or no, should pummel you for anything. The answer to your
question here is yes, you can predict how a glaze will react once it is
fired. All of the materials that we use have what is called a coefficient of
expansion. When you use groups of elements and oxides in glazes you can
mathematically deduce the coefficient of expansion of the glaze. There are
plenty of texts on glazes that cover this stuff, so I won't put you to sleep
here. BUT, you are never really "home free" because what you do on paper may
never fully or accurately represent what comes out of the Earth. But, using
the tools that we have at our disposal, you don't have to find your way home
in total darkness. Remember though, today's analysis may not be true and
accurate next week because of varying compostion in natural minerals, which
will affect their coefficient of expansion, among other things.
Both Claybody and Glaze are made up of some of the same minerals. To
understand either, one must have some knowledge of both. I recently sent a
post to Clayart in regard to two articles written for Studio Potter by Jim
Robinson, that deal with the behavior of claybodies and glazes. "Fear of
Silica" June 1981 and "Body Building for Potters", June 1988 both have
incredibly valuable and readable information for studio clay artists and
potters. If you have the time to read them, I know that these articles will
answer several of your questions. You are already on track and have a grasp
of the possibilities. I think a little reading will firm things up nicely.
Best Regards, Craig Martell-Oregon
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