Wanda Holmes on tue 4 jun 02
I have formulated a cone 6 oxidation base glaze that I hope will yield a
good strong alkaline color response. I started with one of Ian Currie's
corner glazes - 90% Frit 3134, 10% Kaolin - and modified it with the goal of
increasing it's stability and durability while lowering it's COE and
maintaining its color response. The glaze I came up with is:
Frit 3134 42
Custer feldspar 18
Nepheline syenite 11
EPK 14
Silica 13
Lithium carbonate 2
Na2O 0.32 Al2O3 0.35 SiO2 3.20
K2O 0.08 B2O3 0.46 P2O5 0.00
MgO 0.00 TiO2 0.00
CaO 0.51 Fe2O3 0.00
Li2O 0.09
Alumina:Silica ratio is 1.00:9.03
Neutral:Acid ratio is 1.00:3.93
Alk:Neut:Acid ratio is 1.00:0.82:3.20
Expansion: 77.4 x 10e-7 per degree C
I will start testing it in the next few days, but in the meantime if any of
you have comments or suggestions, I would love to hear them.
Thanks,
Wanda
Ian Currie on thu 6 jun 02
Hi Joyce
I've used those 90% frit + 10% kaolin glazes for some time as a starting
point to get turquoise with copper. As I mention in the book, I use ferro
frit 3110 for more transparent, and 3134 for more opaque. I usually blend
them to balance these features.
So far I've never had them tested for stability, but because the alumina and
silica are low, I assume there might be a problem... and I do not use them
inside functional bowls, bottles etc. However I have had them in use for
years without any indication of instability. I suspect John Hesselberth
might be able to squeeze something out of them though!
The problem with strong alkaline colour response (e.g. strong turquoise from
copper) is that the colours generally do not like alumina. If you do a grid
based on the glazes above, you find that the turquoise changes to green as
you move from the bottom to the top of the grid (alumina increasing).
However one of the uses of the grid is to show you in the most direct way
possible what the trade-offs are... you can make your choices.
With what you've done, the alumina is increased by bringing in the feldspar
and neph. syenite... but I think it is worth a try. I suspect it will give
simply a less intense alkaline response than the high-frit one.
I get the impression from some tests that barium will allow you to increase
the alumina while keeping an alkaline colour response... but with the
obvious need for caution again... here if it releases barium it may well be
poisonous. Barium also allows you to obtain matt alkaline colours... not
easy otherwise unless you are underfiring... a no-no if you are trying for
stability. (One of Ron & John's four rules for making a stable glaze:
"Thoroughly Melt the Glaze".)
And as consolation I suggest you look at a book with some of the old
middle-eastern islamic mosques covered with brilliant turquoise tiles. You
will often note that near the top of the roof where the tiles are more
horizontal the glaze has broken down, and possibly the terracotta tile too,
and far from turquoise tile what you have is a sort of weed garden! So they
had stability problems too!
In the few experiments I've done, I've found that in a given alkaline glaze,
the alkaline colour decreases with temperature rise.
What you've chosen to explore is difficult but I believe doable. Good luck!
Ian
http://ian.currie.to/
> From: Wanda Holmes
> Reply-To: Ceramic Arts Discussion List
> Date: Tue, 4 Jun 2002 21:57:44 -0500
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Glaze Gurus - Alkaline color response
>
> I have formulated a cone 6 oxidation base glaze that I hope will yield a
> good strong alkaline color response. I started with one of Ian Currie's
> corner glazes - 90% Frit 3134, 10% Kaolin - and modified it with the goal
of
> increasing it's stability and durability while lowering it's COE and
> maintaining its color response. The glaze I came up with is:
>
> Frit 3134 42
> Custer feldspar 18
> Nepheline syenite 11
> EPK 14
> Silica 13
> Lithium carbonate 2
>
> Na2O 0.32 Al2O3 0.35 SiO2 3.20
> K2O 0.08 B2O3 0.46 P2O5 0.00
> MgO 0.00 TiO2 0.00
> CaO 0.51 Fe2O3 0.00
> Li2O 0.09
>
> Alumina:Silica ratio is 1.00:9.03
> Neutral:Acid ratio is 1.00:3.93
> Alk:Neut:Acid ratio is 1.00:0.82:3.20
>
> Expansion: 77.4 x 10e-7 per degree C
>
> I will start testing it in the next few days, but in the meantime if any
of
> you have comments or suggestions, I would love to hear them.
>
> Thanks,
> Wanda
>
>
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