Fred Hagen on sat 14 jan 06
I recently fired the studio's Bailey downdraft kiln with mostly shino glazes in it and didn't get much of what I wanted. Some of my flattened bottles where white (not enough reduction?) some of the shinos turned slime green etc. On some of my bowls the inside was what I was looking for but the outside was green.
I was using the Davis cabon trap shino, and:
A spotted shino
Neph Sye 40
Spod 30
OM4 17
Soda Ash 8
EPK 5
I also used a Sharkskin recipe that I got out of The Amer. Shino book
Neph Sye 75
OM-4 --25
Soda Ash --6
I even soaked some of the pieces for the sharkskin in a solution of water and Soda Ash for up to 1/2 hour first then let it dry of course then the glaze.. This I've tried before ,also with bad luck.
I used John Britt's firing profile #1 with the reduction heavy at 012 for an hour then tapered until it reached cone 9+ as 10 was leaning.
Most of the work was with B Mix. Should it be a high iron clay body? Don't think so as I see many pictures of great work with porcelain.
So what causes the greens and whites?
Thanks Fred Hagen
JOYCE LEE on sat 14 jan 06
Fred mentions that he fired his shinos to ^9 with ^10 leaning. Believe =
me, I've
fired many a load of shinos..... am obssessed with shino...... but am so =
far
from knowing sh** about shino that it's hardly worth listening to me. =20
BUT .... maybe noteworthy...... is the fact that I never had much except =
the
gray/white or slime green colors ..... until I accidentally fired to at =
least ^12
in my Geil gas reduction kiln. I had made assumptions about my kiln =
..... that
because it was listed as ^10 that it wouldn't fire higher than that, for =
one......=20
PLUS, even if I hadn't assumed as I did, I had no idea that the heat =
could jump from=20
10 to 12 so rapidly!! That first load at at least ^12 (it was ^12 flat =
and I didn't
have a ^13 available so who knows?) was luscious.=20
I've since had different interesting
results also, not necessarily the same as my first "overfired" load. =
I've had
more carbon trapping than I wanted at times (not all that great looking =
by
itself) as well as a variety of pinholes from time to time. Oddly =
enough, I like
the pinholes ..... those pots tend to appear much more rustic looking =
than
my usual shinos........ whatever a "usual" shino is.
I generally use a shino recipe of Mel's called Wirt's Shino (I think) =
because she
originated it....... this was the first load of overfired shino and is =
consistently the
closest to the ones that Mel fires in his kilns. I've also used
Davis' recipes, each of which was at minimum "interesting." And Hank
Murrow's shino that doesn't really look like shino from my firings, but =
has a
texture and fudgy look for me that is very appealing.
As I become more secure once again in my throwing and firing I expect to =
tackle the
shinos in John Britt's ^10 book. So many shinos, so little time. =
However, I've given
up giving up on shinos. I'll continue to branch out where only the =
gurus fear to tread.....
but shino will always be part of my life. We are As One ...... =
forever....... and a day.....
or more.......
Joyce
In the Mojave desert of California USA where Donald's rain from the San =
Fernando
Valley is supposed to be hitting us before many hours .... can I BE more =
joyful??
John Britt on sat 14 jan 06
Fred,
Sounds to me like you did not get even reduction (if some were white) and
you are using too much soda ash. What is the oxiprobe read?
Excessive soda ash will make the snot green you describe. I would try it
again without soaking it in soda ash. And try to get heavier reduction.
Hope it helps,
John Britt
www.johnbrittpottery.com
Dave Finkelnburg on sun 15 jan 06
Fred,
I think you've gotten most of the right answers to your question. Simply put, it's not your recipes, it's glaze thickness...and possibly...firing. Carbon trapping a thickly applied high-soda ash Shino will almost always produce a shade, not necessarily a good one, of green. :-(
Malcolm Davis was quick to point this out in a workshop I was fortunate enough to take from him....you need to track glaze density, bisque absorption, and glaze application (such as dipping time) to monitor the resulting glaze thickness during application. Malcolm uses a very soft bisque (~ cone 012), low density glaze and several seconds (up to 10, as I recall) dipping time to get results he likes. There are other ways.
I would have to say that 30-minutes in a soda ash solution sounds excessive. :-) Even that many seconds is probably more than you want.
Regarding B-mix, I don't know why but I prefer stoneware or straight porcelain for soda ash Shinos. I have used tons of C10 B-mix but I don't use it for Shinos and can't really say why. Somewhere I developed this prejudice but haven't documented it. You should test other bodies, certainly. With your profile you should have had good carbon trapping.
Might I suggest that you make test tiles and apply glazes, soda ash, etc. to intentionally different, and carefully marked and recorded, thicknesses? Then sacrifice a firing to the test tiles and try to learn what thickness you need for your clay and glaze. I think this would help you sort this out fastest.
Good potting!
Dave Finkelnburg
Fred Hagen wrote:
I recently fired the studio's Bailey downdraft kiln with mostly shino glazes in it and didn't get much of what I wanted. Some of my flattened bottles where white (not enough reduction?) some of the shinos turned slime green etc. On some of my bowls the inside was what I was looking for but the outside was green.
Most of the work was with B Mix. Should it be a high iron clay body? Don't think so as I see many pictures of great work with porcelain.
So what causes the greens and whites?
---------------------------------
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Donald G. Goldsobel on sun 15 jan 06
Fred,
The green slime is the soda ash that didn't get to be reduced and get to be
part of the glaze. The white was the shino- the cause of both is
insufficient reduction. I agree with Dave, that 30 minutes in soda is way
too much. King Malcolm pointed out that the soda migrates from the glaze to
the surface of the pot. The longer you let it sit between glazing and
firing, the greater the amount of soda on the surface. If there is no iron
present, you get a white glaze. If it reduces properly, the color comes from
the carbon that is trapped. The reduction has to be enough to create an
atmosphere that is rich in unburned fuel, i.e. carbon particles, that will
mix with the molten soda ash on the surface and be trapped and there it
is-carbon trapping..
Good luck
Donald
Lee Love on sun 15 jan 06
On 2006/01/15 3:10:06, lkshorepottery@sbcglobal.net wrote:
>
> Most of the work was with B Mix. Should it be a high iron clay body?
Don't think so as I see many pictures of great work with porcelain.
Along with what others have mentioned: MD's glaze for porcelain has
Red Art clay in it for iron. Traditional shino fire color comes from
both iron and alumina. You can either use MD's red art glaze, use
an iron body, or decorate with an iron slip on a white body (as they
did traditionally.)
Soaking in soda ash will sometimes get you snot
green. On an iron body, you are more likely to get color on the
thin spots while the thick parts of the glaze are whiter.
Try a neph sye/ball clay line-blend: from 75/25 to
25/75, with 6% soda in each. You could swap EPK for ball clay too.
See if you get more color with more alumina. My American formulas did
not translate well to my new kiln, but when I used more kaolin, I
started getting more color. I got this idea from looking at flashing
slip recipes.
--
Lee Love
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
"Simplicity is the ultimate sophistication."
--Leonardo da Vinci
Liz Willoughby on mon 16 jan 06
Hello Fred,
I guess I might as well put my two cents worth in too. I also have a
Bailey studio kiln. As you have found out there are many variables
with using shino glaze.
The Sharskin shino, I have found to fire mostly white, with some
carbon trapping, if you are lucky.
I use mostly porcelain and usually do not add the red art to my m.d.
glaze. I do alter the glaze by replacing half the EPK with alumina.
Here is what I do. Bisque at cone 04. Glaze by dipping. One dip and
my pieces tend to be more orange, two dips and they tend to be more
white, but also have more carbon trapping. I will double dip the rim
of a bowl, for instance, for more carbon trapping. If I have a vase
I will glaze the inside first, glaze the outside, and then when it
sets up, do a light spraying of glaze over the outside. Sometimes I
get beautiful spots doing this.
The snotty green is too much soda ash. If you want to use just use
soda ash, just brush it on a stoneware, for a wood-fired look.
Important things that I have learned. Glaze your shino pieces the
day before or the day of stacking, for better carbon trapping.
Candle for 1/2 day, have burners on low overnight, turn them up at 6
in the morning. (Like Mel, I like to have my firing over late
afternoon). My brain tells me that by candleing a long time and
having the burners on low overnight, using the moisture in the kiln
from the recently glazed pots, to help create carbon, which in turn
helps to create carbon trapping when I go into reduction at cone 012.
It is fun to fool around with the wax resist. use it, then dip again.
Press your thumb on a glaze after you have glazed, interesting
effect. lots of things you can do. But especially find out where
your sweet spots are in the kiln. Try the top for the vases. I find
that it is a good spot for carbon trapping, also the front by the
door.
Put lots of glaze tests in, next to cone packs. After doing all
this, you still will be frustrated, if you want 100 % perfect carbon
trapping in your kiln. I can have two pots sitting side by side,
glazed the same time, the same way, and come out completely
different. I really have just learned to accept what I get, but to
keep trying.
Do you have Studio Potter, Vol. 21
#1? Good article in there on shinos by Jim Robinson.
Also a more recent Studio Potter, Vol 30 #2, has articles in it by
various potters, some with recipes, curated by Malcolm Davis.
Carbon Trap Glaze Addict otherwise known as Miticky Liz from Grafton,
Ontario, Canada
>I recently fired the studio's Bailey downdraft kiln with mostly
>shino glazes in it and didn't get much of what I wanted. Some of my
>flattened bottles where white (not enough reduction?) some of the
>shinos turned slime green etc. On some of my bowls the inside was
>what I was looking for but the outside was green.
> I was using the Davis cabon trap shino, and:
>
> A spotted shino
> Neph Sye 40
> Spod 30
> OM4 17
> Soda Ash 8
> EPK 5
>
> I also used a Sharkskin recipe that I got out of The Amer. Shino book
> Neph Sye 75
> OM-4 --25
> Soda Ash --6
> I even soaked some of the pieces for the sharkskin in a solution
>of water and Soda Ash for up to 1/2 hour first then let it dry of
>course then the glaze.. This I've tried before ,also with bad luck.
> I used John Britt's firing profile #1 with the reduction heavy at
>012 for an hour then tapered until it reached cone 9+ as 10 was
>leaning.
>
> Most of the work was with B Mix. Should it be a high iron clay
>body? Don't think so as I see many pictures of great work with
>porcelain.
>
> So what causes the greens and whites?
>
> Thanks Fred Hagen
Lee Love on mon 16 jan 06
On 2006/01/16 1:53:30, idahopottery@yahoo.com wrote:
> Malcolm Davis was quick to point this out in a workshop I was
fortunate enough to take from him....you need to track glaze density,
>bisque absorption, and glaze application (such as dipping time) to
monitor the resulting glaze thickness during application. Malcolm
>uses a very soft bisque (~ cone 012), low density glaze and several
seconds (up to 10, as I recall) dipping time to get results he likes.
>There are other ways.
If you do a scratch test of the glaze surface, it is the best
way to know the actual thickness of the application. It takes time to
learn. One thing you can do is dip two tiles for every test. Scratch
test them and then save one set unfired to measure future applications
against.
> I would have to say that 30-minutes in a soda ash solution sounds
excessive. :-)
This can be done without glaze application and the soda
soak by itself will have a soda fired look. I experiment with this
and my best experiments were on porcelain or superwhite stoneware.
--
Lee Love
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
"Simplicity is the ultimate sophistication."
--Leonardo da Vinci
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