Gail Dapogny on mon 5 jun 00
Is it possible that this was caculated for once-firing? I know that
bentonite is doubled in recipes for such firing. ---Gail
>This glaze, 'cone 10 reduction Sage Green Matt' (below),
>caught my eye because of the extraordinarily high
>amount of clay in the recipe. 22% ball clay, plus 21%
>kaolin, then 5.3% bentonite thrown in.
>
>This is not a criticism, but I would really like to know
>why 5.3% bentonite might be added to a recipe that already
>contains a whopping 43% clay.
>I recalculated the recipe to get rid of the bentonite and ball clay
>and came up with:
>
>Minspar 200 34
>flint 10
>talc 6.7
>whiting 6.3
>Gerstley Borate 5
>EPK kaolin 38
>titanium dioxide 10.4
>cobalt carbonate 2.10
>David Hendley
>Maydelle, Texas
>hendley@tyler.net
>http://www.farmpots.com/
David Hendley on mon 5 jun 00
This glaze, 'cone 10 reduction Sage Green Matt' (below),
caught my eye because of the extraordinarily high
amount of clay in the recipe. 22% ball clay, plus 21%
kaolin, then 5.3% bentonite thrown in.
This is not a criticism, but I would really like to know
why 5.3% bentonite might be added to a recipe that already
contains a whopping 43% clay.
BTW, the formula for this glaze shows that it contains a
huge amount of alumina, at .95 molecular equivalents:
Cao .43
MgO .28
KNa2O .30
TiO2 .63
B2O3 .10
Al2O3 .95
SiO2 4.39
I recalculated the recipe to get rid of the bentonite and ball clay
and came up with:
Minspar 200 34
flint 10
talc 6.7
whiting 6.3
Gerstley Borate 5
EPK kaolin 38
titanium dioxide 10.4
cobalt carbonate 2.10
I plan on trying a test of my recalculation. I'm interested
in cobalt green glazes and will be interested to see how
this high alumina glaze will look for me.
I'm also curious about the very large amount of titanium.
I can't help but expect that pinholes might be a problem
with so much titanium.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
> Here is a cone 10 Reduction Sage Green Smooth Matt
>
> Gerstley Borate 5.3
> Talc 6.3
> Whiting 7.4
> Neph Sye 26.3
> OM4 22.1
> EPK 21.0
> Flint 11.6
> Bentonite 5.3
>
> Add: Cobalt Carb 2.1
> Titanium 10.5
>
>
Donald Burroughs on mon 5 jun 00
Hi David
Came across your message regarding cone 10 green glaze. Would really like
to know your results.I really am a fan of the colour green especially in the
high fire range.
Sincerely, Donald Burroughs
donaldo@autobahn.mb.ca
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of David Hendley
Sent: June 5, 2000 12:25 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Sage Green Smooth Matt glaze
This glaze, 'cone 10 reduction Sage Green Matt' (below),
caught my eye because of the extraordinarily high
amount of clay in the recipe. 22% ball clay, plus 21%
kaolin, then 5.3% bentonite thrown in.
This is not a criticism, but I would really like to know
why 5.3% bentonite might be added to a recipe that already
contains a whopping 43% clay.
BTW, the formula for this glaze shows that it contains a
huge amount of alumina, at .95 molecular equivalents:
Cao .43
MgO .28
KNa2O .30
TiO2 .63
B2O3 .10
Al2O3 .95
SiO2 4.39
I recalculated the recipe to get rid of the bentonite and ball clay
and came up with:
Minspar 200 34
flint 10
talc 6.7
whiting 6.3
Gerstley Borate 5
EPK kaolin 38
titanium dioxide 10.4
cobalt carbonate 2.10
I plan on trying a test of my recalculation. I'm interested
in cobalt green glazes and will be interested to see how
this high alumina glaze will look for me.
I'm also curious about the very large amount of titanium.
I can't help but expect that pinholes might be a problem
with so much titanium.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
> Here is a cone 10 Reduction Sage Green Smooth Matt
>
> Gerstley Borate 5.3
> Talc 6.3
> Whiting 7.4
> Neph Sye 26.3
> OM4 22.1
> EPK 21.0
> Flint 11.6
> Bentonite 5.3
>
> Add: Cobalt Carb 2.1
> Titanium 10.5
>
>
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Ray Aldridge on tue 6 jun 00
>It's not unusual to see shino glazes with .9 or so moles of alumina and
>sometimes more than that. Perhaps the cobalt green is favored by a lower
>silica/alumina ratio.
I might be wrong, (and maybe I'm not even thinking of the same recipe) but
my guess is that the reason this is a green glaze is simply because of the
large amount of titanium. I use a slip with 8% added titanium and it's a
fairly bright yellow. Yellow and blue make green.
Maybe this is too simple, but I'd bet if you just left the titania out of
this recipe, you'd have a blue glaze. As another example of the phenom,
some folks (and I'm one) think that the major difference bewtween a blue
celadon and a green celadon is just the amount of titania in the glaze.
Like others who've posted on this subject, I can't imagine why the recipe
needs the bentonite. There can't be a whole lot of clay bodies with so
much shrinkage that a raw glaze needs more clay than this, (and I don't
think I'd want to have to work with them.) I wonder how well-behaved this
glaze would be over bisque.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Craig Martell on tue 6 jun 00
David sez:
>This is not a criticism, but I would really like to know
>why 5.3% bentonite might be added to a recipe that already
>contains a whopping 43% clay.
Hi:
Perhaps the glaze was originally formulated for raw application. Maybe the
clay body that this glaze was formulated for had a high plastic to bone dry
shrinkage and even with 43% clay a bit more shrinkage in the glaze was
needed by adding bentonite. Seems odd though because the ball clay should
do some of that.
It's not unusual to see shino glazes with .9 or so moles of alumina and
sometimes more than that. Perhaps the cobalt green is favored by a lower
silica/alumina ratio. An Ian Currie biaxial of the receipe would divulge
this. Maybe the glaze is just a seat of the pants formulation too. Hard
to say sometimes.
regards, Craig Martell in Oregon
Craig Martell on wed 7 jun 00
Ray remarked:
>I might be wrong, (and maybe I'm not even thinking of the same recipe) but
>my guess is that the reason this is a green glaze is simply because of the
>large amount of titanium.
Hi Ray:
Exactly, the titanium is the major factor in making the green. But I've
seen other glazes, reitz green for example that use a small amount of
titanium or rutile(titanium and iron) against the cobalt and they will make
lovely greens. These glazes are high in alumina and that makes me lean
toward the idea of a low silica/alumina ratio to favor this color. Needs
to be proven with testing though. Merely an educated hypothesis at this
point. Well, maybe not educated.
>Maybe this is too simple, but I'd bet if you just left the titania out of
>this recipe, you'd have a blue glaze. As another example of the phenom,
>some folks (and I'm one) think that the major difference bewtween a blue
>celadon and a green celadon is just the amount of titania in the glaze.
I believe that you are correct about no titania making the glaze
blue. Cobalt is a strong persuader. In the case of celedons, the absense
of titania is important in the development of a blue celedon but does not
guarantee blue. I've done a lot of work on celedons and what I've seen,
and this is documented by others, (Tichane and Currie) glazes must be high
in potash to produce the blue from Fe. I have three celedons I've been
working on with grolleg kaolin, which is very low in TiO2 and I've been
introducing the Fe with Alberta Slip, which is almost devoid of
TiO2. Still getting green, but very lovely greens. When I up the potash I
have problems with glaze fit so I'm still flogging around in left field. I
use slips containg Fe for color because the iron will disperse wonderfully
without ball milling. If I use red or black iron, I have to ball mill the
glazes or screen them several times through a 200 mesh to eliminate
spotting. It is said though, that black iron is better for blue
celedons. I don't know this to be true from experience.
later, Craig Martell in Oregon
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