Craig Martell on mon 24 jul 00
Hello:
> your choice of clay is critical - preferably it should be a highly=20
> plastic (high percentage of colloidal clay particles) with a nice high=20
> carbon content
I don't think that the clay choice is "critical". It can be an important=20
factor but not critical to the development of shinos and carbon trap. I've=
=20
done some biaxials of shinos with the idea of looking at color development=
=20
in relation to alumina and silica in the glazes. We did one 35 glaze=20
biaxial grid using no clay at all. The alumina was supplied by Neph sy and=
=20
pure alumina oxide. We were looking at the development of the red shinos=20
in the areas of higher alumina and the tests proved that this was so. We=20
also saw some carbon inclusion sans clay in the glazes. So that's why I=20
think it isn't critical but I certainly don't discount your thinking on the=
=20
contribution of colloidal clays with a high LOI.
>The reason for using nepheline syenite as a flux in these glazes is to=20
>keep the silica-content low and alumina high - the alumina/iron/sodium=20
>ratio is critical f=F6r the development of the orange colours.
I have to agree here. These oranges and reds from small amounts of iron=20
develop when the iron is not allowed to go into solution. So you want a=20
good amount of alumina and as little calcium as possible to facilitate=20
this. What I saw in the 35 glaze biaxial grid that we did with pure=20
alumina oxide was red shinos in the higher alumina blends and as the silica=
=20
increased in the other glazes on the tile I saw the glazes go from red to=20
hot orange to lighter orange as the silica increased. What really amazed=20
me was glaze #1 which was 40% alumina oxide and it still melted and was a=20
lovely, though crawled from hi surface tension, red.
regards, Craig Martell in Oregon
Dan Hill on sat 29 jul 00
Someone was looking for the issue of Ceramics Monthly with the article
by Gail Nichols on soda glazing. It was Nov. 1999 Volume 47 Number 9.
Dan.
Craig Martell wrote:
>=20
> Hello:
>=20
> > your choice of clay is critical - preferably it should be a highly
> > plastic (high percentage of colloidal clay particles) with a nice hig=
h
> > carbon content
>=20
> I don't think that the clay choice is "critical". It can be an importa=
nt
> factor but not critical to the development of shinos and carbon trap. =
I've
> done some biaxials of shinos with the idea of looking at color developm=
ent
> in relation to alumina and silica in the glazes. We did one 35 glaze
> biaxial grid using no clay at all. The alumina was supplied by Neph sy=
and
> pure alumina oxide. We were looking at the development of the red shin=
os
> in the areas of higher alumina and the tests proved that this was so. =
We
> also saw some carbon inclusion sans clay in the glazes. So that's why =
I
> think it isn't critical but I certainly don't discount your thinking on=
the
> contribution of colloidal clays with a high LOI.
>=20
> >The reason for using nepheline syenite as a flux in these glazes is to
> >keep the silica-content low and alumina high - the alumina/iron/sodium
> >ratio is critical f=F6r the development of the orange colours.
>=20
> I have to agree here. These oranges and reds from small amounts of iro=
n
> develop when the iron is not allowed to go into solution. So you want =
a
> good amount of alumina and as little calcium as possible to facilitate
> this. What I saw in the 35 glaze biaxial grid that we did with pure
> alumina oxide was red shinos in the higher alumina blends and as the si=
lica
> increased in the other glazes on the tile I saw the glazes go from red =
to
> hot orange to lighter orange as the silica increased. What really amaz=
ed
> me was glaze #1 which was 40% alumina oxide and it still melted and was=
a
> lovely, though crawled from hi surface tension, red.
>=20
> regards, Craig Martell in Oregon
>=20
> _______________________________________________________________________=
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> Send postings to clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list or change your subscription
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>=20
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