gina mars on tue 29 mar 11
Hi All, I'm having an issue at my school with the Cherry Blossom Shino
glaze published
in Ceramics monthly a while back, maybe last year. The glaze is
applied to 181 standard white
stoneware and also 306 brown clay. The glaze has chipped off the 181
clay when the pieces
come out of the cone 6 gas reduction kiln.
The interesting thing is, I made a batch at home and did not heat up
the chunky soda ash
in hot water before I mixed it and sieved it. At work, we got the soda
ash clumps out by
putting the soda ash in hot water. I glazed work with both batches and
noticed that MY
batch had a crackle white effect with carbon trapping and very little
brown color. The school
batch, was a nice toasty brown with no carbon trapping and almost an
irredescent quality to it.
Regardless off the glaze, they both had areas on peoples work that you
could chip off,kind
of like slate, underneath there seemed to be some residue that looked
like salt or spit. I
assume this is the soda ash . The brown clay to my knowledge did not
have this problem
but I could be wrong. I realize shinos should have one dip but I'm not
good at keeping track of
all students and their applications. One piece was touched up with
more shino and refired in oxidation. the
area came out a slight green color and covered the problem. This glaze
issue can cut
a student and also is not food safe. Would anyone have any ideas as to
what is going on
with this glaze?
Sincerely, Gina Mars
www.marspottery.net
sitting out NCECA this year but did the mug exchange.
Paul Herman on tue 29 mar 11
Gina,
I assume you mean the glaze formula below.
Cherry Blossom Shino
40.00 Nepheline Syenite
40.00 Spodumene
10.00 EPK Kaolin
10.00 Soda Ash
It's the 40% spodumene that is causing the shivering of your glaze.
Spodumene is high in lithium, a low expansion material. The clay body
is contracting more than the glaze in your cooling cycle, and the
glaze flakes off from being put into too much compression. Shinos that
are high in spodumene are known to shiver at higher temps (^10) too.
I would abandon that glaze, or reduce the lithium considerably.
best,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Mar 29, 2011, at 5:44 AM, gina mars wrote:
> Hi All, I'm having an issue at my school with the Cherry Blossom Shino
> glaze published
> in Ceramics monthly a while back, maybe last year. The glaze is
> applied to 181 standard white
> stoneware and also 306 brown clay. The glaze has chipped off the 181
> clay when the pieces
> come out of the cone 6 gas reduction kiln.
> The interesting thing is, I made a batch at home and did not heat up
> the chunky soda ash
> in hot water before I mixed it and sieved it. At work, we got the soda
> ash clumps out by
> putting the soda ash in hot water. I glazed work with both batches and
> noticed that MY
> batch had a crackle white effect with carbon trapping and very little
> brown color. The school
> batch, was a nice toasty brown with no carbon trapping and almost an
> irredescent quality to it.
> Regardless off the glaze, they both had areas on peoples work that you
> could chip off,kind
> of like slate, underneath there seemed to be some residue that looked
> like salt or spit. I
> assume this is the soda ash . The brown clay to my knowledge did not
> have this problem
> but I could be wrong. I realize shinos should have one dip but I'm not
> good at keeping track of
> all students and their applications. One piece was touched up with
> more shino and refired in oxidation. the
> area came out a slight green color and covered the problem. This glaze
> issue can cut
> a student and also is not food safe. Would anyone have any ideas as to
> what is going on
> with this glaze?
> Sincerely, Gina Mars
> www.marspottery.net
> sitting out NCECA this year but did the mug exchange.
Ron Roy on sun 3 apr 11
Hi Gina,
Something fishy here - you said it worked OK at home on what clay, at
cone 6 reduction?
You say it came off 181 but that did not happen on the 306 clay?
If it was used on the 306 did it look the same as yours at home?
Any difference in the speed of heating and cooling of the two kilns?
Let me know the details - could be the 181 if the shivering did not
happen on the 306.
RR
Quoting gina mars :
> Hi All, I'm having an issue at my school with the Cherry Blossom Shino
> glaze published
> in Ceramics monthly a while back, maybe last year. The glaze is
> applied to 181 standard white
> stoneware and also 306 brown clay. The glaze has chipped off the 181
> clay when the pieces
> come out of the cone 6 gas reduction kiln.
> The interesting thing is, I made a batch at home and did not heat up
> the chunky soda ash
> in hot water before I mixed it and sieved it. At work, we got the soda
> ash clumps out by
> putting the soda ash in hot water. I glazed work with both batches and
> noticed that MY
> batch had a crackle white effect with carbon trapping and very little
> brown color. The school
> batch, was a nice toasty brown with no carbon trapping and almost an
> irredescent quality to it.
> Regardless off the glaze, they both had areas on peoples work that you
> could chip off,kind
> of like slate, underneath there seemed to be some residue that looked
> like salt or spit. I
> assume this is the soda ash . The brown clay to my knowledge did not
> have this problem
> but I could be wrong. I realize shinos should have one dip but I'm not
> good at keeping track of
> all students and their applications. One piece was touched up with
> more shino and refired in oxidation. the
> area came out a slight green color and covered the problem. This glaze
> issue can cut
> a student and also is not food safe. Would anyone have any ideas as to
> what is going on
> with this glaze?
> Sincerely, Gina Mars
> www.marspottery.net
> sitting out NCECA this year but did the mug exchange.
>
William & Susan Schran User on mon 4 apr 11
On 4/3/11 10:20 PM, "Ron Roy" wrote:
>Something fishy here - you said it worked OK at home on what clay, at
>cone 6 reduction?
Gina Mars wrote:
>> Hi All, I'm having an issue at my school with the Cherry Blossom Shino
>> glaze published
>> in Ceramics monthly a while back, maybe last year.
When we switched to ^6 reduction at school, we tested a number of glazes,
Cherry Blossom Shino being one. Seemed to work well, mixed larger batch and
after sitting for a while the glaze began to shiver on most all clays.
We switched to another that has been working on several clay bodies.
It is listed on my web site on the ^6 reduction page.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
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