iandol on mon 25 dec 00
Alisa wrote, relating to cobalt in conjunction with a =
rutile/cobalt/ballclay slip on a dolomite glaze drawing varied from dark blue to violet to green.>
Dear Alisa
Thanks for that clue to this elusive effect. I have known for a long =
time that a Cobalt green is possible. Now can this be explained. Is it =
the mixture of Magnesium and Calcium, or one of these independently, is =
it the Rutile. Or is it either the additional Aluminium or Silicon from =
your ball clay. Or is there something in the ball clay which is causing =
the green to emerge.
An interesting mystery. Is this cone 6 oxidation?
Best regards,
Ivor.
Nanci Bishof on mon 25 dec 00
I get beautiful greens that I can vary by the ratio of Rutile and Cobalt
Carbonate. They have a nice motttled look akin to high fire at low - mid fire
ranges, ^0- ^6.
nanci
John Hesselberth on mon 25 dec 00
iandol wrote:
>Thanks for that clue to this elusive effect. I have known for a long time
>that a Cobalt green is possible. Now can this be explained. Is it the
>mixture of Magnesium and Calcium, or one of these independently, is it the
>Rutile. Or is it either the additional Aluminium or Silicon from your ball
>clay. Or is there something in the ball clay which is causing the green to
>emerge.
>
>An interesting mystery. Is this cone 6 oxidation?
Hello Ivor,
Here is another clue for you. This glaze was posted by Lee Bedford last
April. Indeed it is green/blue.
Oil Spot Green/Blue ^6
3134 50
EPK 40
Silica 20
Cobalt Carb 3
Rutile 5
Regards, John
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
Tommy Humphries on mon 25 dec 00
As for cobalt green, Wh en messing with the glaze we use at work, I wanted a
good strong blue so I added 3% cobalt ox. to the glaze, and it worked fine.
Got a good strong blue with specks from not screening the cobalt. Then
wanting to add more texture to the clay, I added 5% titanium diox. and got a
very fine textured green. I believe that the titanium and the zinc in the
glaze did the trick on the cobalt, as I had gotten a good deep blue with a
zinc free version of the same glaze using the same recipe.
I believe that the base recipe I was using is in the archives somewhere...It
is Marshall Pottery (Bristol) glaze.
Tommy Humphries
Photos here http://albums.photopoint.com/j/AlbumIndex?u=939179&a=6869600
----- Original Message -----
From: "iandol"
To:
Sent: Monday, December 25, 2000 12:26 AM
Subject: Cobalt Green.
Alisa wrote, relating to cobalt in conjunction with a rutile/cobalt/ballclay
slip on a dolomite glaze violet to green.>
Dear Alisa
Thanks for that clue to this elusive effect. I have known for a long time
that a Cobalt green is possible. Now can this be explained. Is it the
mixture of Magnesium and Calcium, or one of these independently, is it the
Rutile. Or is it either the additional Aluminium or Silicon from your ball
clay. Or is there something in the ball clay which is causing the green to
emerge.
An interesting mystery. Is this cone 6 oxidation?
Best regards,
Ivor.
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Jim V Brooks on tue 26 dec 00
Nanci.... i think you get the greens because of the titanium in the rutile.
I have found that i usually get green, with even small amounts of cobalt,
when i have about 6% titamium in the glaze,.. Interesting test anyway..
Jim in Denton...
C TRIPP on tue 26 dec 00
iandol wrote: "Thanks for that clue to this elusive effect. I have known for
a long time that a Cobalt green is possible. Now can this be explained. Is
it the mixture of Magnesium and Calcium, or one of these independently, is
it the Rutile. Or is it either the additional Aluminium or Silicon from your
ball clay. Or is there something in the ball clay which is causing the green
to emerge.
An interesting mystery. Is this cone 6 oxidation?"
Hello Ivor,
I'll take a stab at this one. I bet it is the titanium in the rutile AND
the amounts of calcium in the glaze. I made two base glazes and added red
iron oxide and titanium to each. The base glaze which was high in calcium
(over the limit for ^6) and had no magnesium showed green/tan over dark
brown. The glaze with within limits calcium and some magnesium showed
blue/tan over dark brown.
I know that I haven't mentioned cobalt. I didn't use any. But the thing I
noticed about the high calcium glaze (Tony Hansen's 5x20) was that it had a
tendancy to be greenish with only red iron oxide added. It was olive green
with brown speckles with red iron oxide and tin added.
Hum, now I am not so sure where this is leading. But it's another idea to
add to the salad.
Regards, Carol
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Nanci Bishof on tue 26 dec 00
I'll check back over my notes, because I am able to get blues too toward the
2% Rutile, but I think thats when I cut back on the Lithium Carbonate too and
added some Silica.
nanci
Diane G. Echlin on tue 26 dec 00
I've used the following glaze with mixed results. It was really runny,
and where thin it was a gorgeous emerald green, and a deep blue almost
purple in the base of the bowl. It did pinhole significantly, and I was
concern about leaching, so I didn't pursue it as a regular addition to
my pallette.
Diane in CT, where it looks like a toy bomb went off yesterday!
John Hesselberth wrote:
>
> Here is another clue for you. This glaze was posted by Lee Bedford last
> April. Indeed it is green/blue.
>
> Oil Spot Green/Blue ^6
>
> 3134 50
> EPK 40
> Silica 20
>
> Cobalt Carb 3
> Rutile 5
>
> Regards, John
>
> "The life so short, the craft so long to learn." Hippocrates, 5th cent.
> B.C.
>
> ______________________________________________________________________________
> 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.
Fraser Forsythe on tue 26 dec 00
This is a green I've recently worked with...it does use copper but the combination
of Lithium and Titanium with the cobalt does produce a very unique green. Never
seen a green like it.
Cone 6-8 in fast fire, reduced. Not tested in oxidation.
Material Name Amount
Cornwall Stone 35
Whiting 13
Bell Dark Ball 24
Flint 27
Bone Ash 5
Lithium Carbonate 5
Cobalt Carb 3.5
Copper Carb 2
Titanium dioxide 10
Fraser
--
Fraser Forsythe
www.glazeexchange.com
fraser@glazeexchange.com
fraserforsythe@icqmail.com
icq# 56080709
June Perry on tue 26 dec 00
I don't have an answer, but I know it's more than just rutile along with the
cobalt. I've been using a beautiful blue glaze for about twenty years and
the colorants are 5% Rutile, 2% Cobalt oxide and 2% copper oxide. It
sometimes shows a bit of green from the copper if it's thin at the rims; but
otherwise it's a beautiful, dark, rich, blue, particularly on porcelain. The
rutile causes other problems, but not color change.
I suspect the cobalt green may have something to do with the acid or
alkaline leaning of the glaze along with the rutile.
It's also been discussed before, with that famous Floating blue glaze, which
has cobalt and rutile, that when chrome is in the kiln, it will turn green.
Regards,
June
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