Ruth Ballou on wed 27 dec 00
Hi all,
I, too, have wondered about cobalt greens and I've used Ian Currie's recipe
method to try to understand what's going on. Craig's definitely right about
it being the fast way to understanding a particular glaze effect. I worked
with a high neph sye glaze with cobalt and rutile as colorants. My first
experiments just modified the colorants, varying the amounts of rutile and
cobalt, and using titanium instead of rutile. Somewhere along the way, I
looked at the recipe for Reitz Green and noticed its high alumina (.8+
moles of alumina). From doing other Currie blends, I've noticed that
alumina frequently has a big impact on color. So I next did some partial
biaxial blends, concentrating on the left side of the grid (increasing the
alumina ). I went over to the right (increasing the silica) for 2 columns,
just so I'd see the effect of increasing the silica, without having to do
all the mixing. If I saw something promising it would be easy to go back
and continue mixing in that area, because I saved my corner glazes. The
grid clearly showed that cobalt will go green in the presence of titanium
as the alumina increases. However, the mattness of the glaze also
increased, to the point of unpleasantness for the group of fluxes I was
using. Then looking again at Reitz Green, I saw that it. too is a high neph
sye glaze, but that it also has boron, lithium and calcium to help flux all
that alumina. The original glaze I was using turned green where it was
thin, which allowed the alumina in the claybody to contribute to the
effect. Reitz Green goes green where the glaze is thick, depending instead
on the alumina in the glaze for the effect. Neat trick if you ask me. Of
course, there may be other flux combinations that will develop the green in
a variety of pleasing surface effects at different temperatures. I think
the critical parameters to look at are a high alumina glaze with cobalt and
titanium as colorants, in which the fluxes are chosen based on their
strength, quantitiy and number. Moderate silcia content. I thank the
biaxial blend for getting me off the slow boat to China and into the
ballpark. There's enough experimentation here without wandering all over
the South Seas!
Ruth Ballou
>If the green color incobalt glazes is to be understood, I think that a very
>systematic approach would yield the best results in the shortest amount of
>time. Do some flux blends, lines, triaxials, quadraxials that produce the
>green, or are close. Then take the promising flux mixtures and do a
>biaxial blend with alumina supplied with clay and silica. Do several of
>these 35 glaze biaxials and start accumulating data that point to zones
>where this type of color forms and other zones where it does not. I use
>Ian Curries Recipe Method for doing this. I can blend the 35 glaze
>biaxials in about 3 hrs. That's not bad and you get a lot of good info.
>Looking for insight into glaze response by trying random samples is the
>famed slow boat to China. I'm not saying that you shouldn't do that if
>it's your bent. But there are faster more thorough ways of getting what
>you want.
>
>Now station the sea and anchor detail!!, Craig Martell in Oregon
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