Linda Knapp on tue 17 dec 02
I am about to try some crystal glazes - just for the fun and
frustration factor ;-) the big limitation/ constraint I have is that I
fire in reduction to about ^11 (I fire in a production potters gas kiln)
as if that wasn't enough we typically have a fast firing / cooling down
cycle.....(Candle overnight, fire up between about 9am and 5pm turn
everything off and open and unload the next morning.) Any pointers /
glaze recipes out there from any of you crystal growers?
Thanks!
Linda
Ilene Mahler on tue 17 dec 02
okay you fire fas to temperature the highest tem i've used is 2345 which is
cone 10 when will you do a soak cycle and for how long and how will you cool
it down fast from the highest temp to the cooling temp..these are things to
think about..don't forget pedistals and saucers for each pot to ketch the
flowing glaze...Ilene in Conn
----- Original Message -----
From: Linda Knapp
To:
Sent: Tuesday, December 17, 2002 9:47 AM
Subject: Crystal Glaze in Reduction?
> I am about to try some crystal glazes - just for the fun and
> frustration factor ;-) the big limitation/ constraint I have is that I
> fire in reduction to about ^11 (I fire in a production potters gas kiln)
> as if that wasn't enough we typically have a fast firing / cooling down
> cycle.....(Candle overnight, fire up between about 9am and 5pm turn
> everything off and open and unload the next morning.) Any pointers /
> glaze recipes out there from any of you crystal growers?
>
> Thanks!
> Linda
>
>
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> Send postings to clayart@lsv.ceramics.org
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william schran on tue 17 dec 02
Linda asked about crystalline glazes for cone 11 reduction.
Crystalline glazes are usually done in oxidation/neutral atmospheres.
Reduction effects are achieved in the lower red heat cool down phase.
Bevan Norkin had an article several years ago about his method of
firing in Ceramics Monthly. Think it was titled "Crystalline Glazes,
a Precise Method". He included his base formula for a cone 11 crystal
glaze.
I do think you will probably not get very satisfactory results in the
"normal" stoneware reduction firing.
Bill
Fabienne Cassman on tue 17 dec 02
There is one article on this subject; however, the person is dripping oil in an electric kiln. The point is that crystals are possible in reduction. At what stage you do it is what matters I believe. I have thre reference to this article listed at http://www.milkywayceramics.com/mf/literature.htm (search for reduction)
Fabienne
---------- Original Message ----------------------------------
>> I am about to try some crystal glazes - just for the fun and
>> frustration factor ;-) the big limitation/ constraint I have is that I
>> fire in reduction to about ^11 (I fire in a production potters gas
--
Fabienne http://www.milkywayceramics.com/
WARNING: I cannot be held responsible for the above
because my cats have apparently learned to type.
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LeRoy Price on tue 17 dec 02
It is very hard for zinc-silicate crystals to grow in a reduction
atmosphere. The reduction gasses "grab" oxygen out of the glaze, causing in
to shrink. This strongly inhibits crystal growth, perhaps because of the
increase in viscosity.
A few people have had some limited success, but the crystals are usually
rather small.
LeRoy Price
----- Original Message -----
From: "Linda Knapp"
To:
Sent: Tuesday, December 17, 2002 6:47 AM
Subject: Crystal Glaze in Reduction?
> I am about to try some crystal glazes - just for the fun and
> frustration factor ;-) the big limitation/ constraint I have is that I
> fire in reduction to about ^11 (I fire in a production potters gas kiln)
> as if that wasn't enough we typically have a fast firing / cooling down
> cycle.....(Candle overnight, fire up between about 9am and 5pm turn
> everything off and open and unload the next morning.) Any pointers /
> glaze recipes out there from any of you crystal growers?
>
> Thanks!
> Linda
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
John Weber on wed 18 dec 02
You may want to look at Crystalline Glazes, by Diane Greber ISBN
0-8122-1648-2 a couple of very nice Copper Red crystalline formulas.
John Hesselberth on wed 18 dec 02
On Tuesday, December 17, 2002, at 08:49 PM, LeRoy Price wrote:
> It is very hard for zinc-silicate crystals to grow in a reduction
> atmosphere. The reduction gasses "grab" oxygen out of the glaze,
> causing in
> to shrink. This strongly inhibits crystal growth, perhaps because of
> the
> increase in viscosity.
>
> A few people have had some limited success, but the crystals are usually
> rather small.
Hi LeRoy,
I suspect the reason is somewhat different. Zinc oxide--the usual way
zinc is introduced into a glaze--is easily reduced to zinc metal. Zinc
metal boils at 907 deg Celsius and therefore much, if not most, of the
zinc probably goes up the stack. Good way to zinc plate your chimney I
guess--or at least the upper, cooler part of it. It's also a good way
to spread zinc oxide around the neighborhood.
To succeed with crystalline glazes in reduction I would think you would
have to avoid a reducing atmosphere until the glaze seals over. That, of
course, also limits the amount of reduction effect you can achieve.
Essentially only the surface of the glaze would be reduced. It would be
a challenging control problem which could probably only be achieved
reliably with the help of an oxyprobe.
Regards,
John
iandol on thu 19 dec 02
Dear John Hesselberth,
The idea of doing no reduction until the glaze has matured is an =
excellent one as far as I can see. Allowing cooking to occur until the =
Zinc Silicate Crystals start to grow means that their chemistry is =
possibly fixed. A little calculation, if you can get hold of the =
Enthalpy values, will help in predicting if the crystals will decompose =
once they have formed when meeting a reducing or low oxygen pressure =
atmosphere. I suspect that, as in the case of formation of other =
silicates, the value is such that one could predict a fair degree of =
stability if a reduction cool were attempted.
The other problem to consider is the actual behaviour of copper =
compounds in silicate melts. Talk recently of percentages greater than =
5% giving black coatings on a glaze are disturbing, almost suggesting =
that Copper oxides are not in fact soluble in Silicate brews.
Gary Elfring on thu 19 dec 02
Hello Linda,
Tuesday, December 17, 2002, 8:47:28 AM, you wrote:
LK> I am about to try some crystal glazes - just for the fun and
LK> frustration factor ;-) the big limitation/ constraint I have is that I
LK> fire in reduction to about ^11 (I fire in a production potters gas kiln)
LK> as if that wasn't enough we typically have a fast firing / cooling down
LK> cycle.....(Candle overnight, fire up between about 9am and 5pm turn
LK> everything off and open and unload the next morning.) Any pointers /
LK> glaze recipes out there from any of you crystal growers?
I did a number of crystal glazes pots in a gas reduction kiln with
excellent results. The standard glaze recipes (David Snair, etc)
worked fine. It's important to remember that a gas reduction kiln is
*not* normally a reducing atmosphere- you deliberately make the kiln
reduce, during part of the firing, by putting in too much gas for the
amount of oxygen in the kiln.
You *do* have to keep the kiln out of reduction. Keep the gas flow
down and the air injection up. You also need very good temperature
control- cones won't work. You typically ramp to a specific
temperature, bring the kiln down 50 - 100 degrees, let it soak for a
while for the crystals to grow, and you might also raise the
temperature up and down slightly a few times during the soak to get
different effects.
--
Best regards,
Gary mailto:info@elfring.com
Fredrick Paget on fri 20 dec 02
This is a thing that I once did a couple of years ago.
I built a very small test kiln using natural gas and it is installed
outside on top of an old brick barbecue that came with my house from a
previous owner.
I made this little kiln to experiment with Moorish Luster glazes and it has
a port in the roof through which you can drop reduction material onto a
shelf placed above the ware and also has peeps in the door.
I took some finished zinc crystal glazed pieces with copper blue green
crystals and placed them in the kiln. Then heated to cone 019 holding
temperature gently falling and started adding reduction material for one
hour. I was using Naphalene moth balls and pieces of Georgia Fat Wood (
sold by Orvis Company as fire starter kindling. It is actually imported
from Guatemala and is a very resinous wood.) I used a good pyrometer to
monitor temperature and at each addition of reduction material the
temperature went up and I let it cool down to 10 degrees less than it was
previously before adding another shot of reduction material.
I have also used Webber fire starter which is some sort of white substance
(synthetic) that is sold to start charcoal barbecue fires. It doesn't smoke
and smell up the neighborhood like the mothballs do.
The result when cooled was a green background with blood red crystals.
Fred Paget
>Dear John Hesselberth,
>
>The idea of doing no reduction until the glaze has matured is an =
>excellent one as far as I can see. Allowing cooking to occur until the =
>Zinc Silicate Crystals start to grow means that their chemistry is =
>possibly fixed. ..........
'
From Fred Paget, Marin County, California, USA
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