Hank Murrow on mon 11 dec 06
On Dec 11, 2006, at 6:36 PM, Chris Trabka wrote:
>
> My question to the group is a starting point for experiments. I have
> searched the archives for matt greens in a reduction atmosphere.
> Answers
> that surfaces are cobalt and titanium (or rutile),
>
> What is an appropriate starting point? The base glaze or the additives?
Chris;
Try Reitz Green and tinker with it. Good in either red or ox fires.
Glaze name: PLAID; aka Reitz Green
Cone: 10
Color: Blue to Charcoal to Moss Green
Testing: Tested
Surface texture: Semi-Matte or Satin
Firing: Ox. or Red; I fire it in Oxidation.
Glaze type: Crystalline Matt.
Recipe: Percent
Nepheline Syenite 70
Petalite 15
Whiting 5
Gerstley Borate 2 (it's better sans GB)
Grolleg Kaolin 8
Totals: 100.00 %
Also add:
Cobalt Carbonate 1
Rutile 2
Comments:
Reitz to Pinnell to Robinson to Hank. Originally a Shino, this version
is a smooooth semi-matt glaze which shows clear to blue to charcoal to
moss green as it goes from thin to thick. Must have a low Ti body and
clay, But........ Has shown a very intense cerulean blue on edges,
don't know why. When glazing the outside of cups I glaze the insides
with Base9 sans Cu for a lovely green overlap. Try leaving out the
Gerstley Borate; and possibly increase the Rutile for a better green.
Alternatively, try Titanium dioxide instead of rutile.
Unity Formula for PLAID:
0.149 K2O 0.872 Al2O3 3.975 SiO2
0.465 Na2O 0.034 B2O3 0.000 TiO2
0.282 CaO 0.003 Fe2O3 0.000 F
0.016 MgO 4.6:1 Si:Al Ratio
0.088 Li2O
Percentage Analysis for PLAID:
60.84 % SiO2
22.65 % Al2O3
0.60 % B2O3
3.58 % K2O
7.34 % Na2O
4.03 % CaO
0.16 % MgO
0.67 % Li2O
0.12 % Fe2O3
Cheers, Hank
www.murrow.biz/hank
Chris Trabka on mon 11 dec 06
A friend of mine has been using Shaner's Green for a number of years has
asked me for help in formulating a new glaze. Sometimes it is not green but
purple (reduction at the right time!).
When I run the Shaner's Green through glaze calculation software I note
that it is short on Silica (which makes the amount of copper an issue). The
recipe is provided below.
In my experience getting a consistent matt green glaze (using copper) in a
reduction atmosphere is difficult (although a celedon is not). I do have
an "ash red" glaze recipe that is most often a matt green, but it will vary
greatly with application (produces tans or greens and sometimes hints of
mauve). The variations are due to the thickness of the galze application.
The recipe is provided below.
I also note that good copper reds seem to rely on the presence of boron
(colemanite or gertsley), tin, and the lack of alumina in an alkaline glaze.
My question to the group is a starting point for experiments. I have
searched the archives for matt greens in a reduction atmosphere. Answers
that surfaces are cobalt and titanium (or rutile), chrome and cobalt, or
named glazes for which there are no recipes (Pinnel's Stronium Matt Green).
What is an appropriate starting point? The base glaze or the additives?
Would I be better served with my "ash red" and trying to get a consistent
substitute for the "ash", or start with a reasonable copper red and try to
transform the red to green and the shiny surface to a matt surface?
Chris
Shaner's RED
BONE ASH............ 9.10
TALC................ 3.50
WHITING............. 18.80
CUSTER FELDSPAR..... 46.50
EPK KAOLIN.......... 22.10
========
100.00
COPPER CARBONATGE 2.90
Ash Red
Ash
===
CUSTER FELDSPAR..... 18.00
EPK KAOLIN.......... 18.00
*Wood Ash............ 20.00
DOLOMITE............ 14.00
FLINT............... 14.00
NEPHELINE SYENITE... 14.00
BENTOLITE ......... 2.00
========
100.00
COPPER CARBONATGE 3.00
TIN OXIDE 1.50
d goldsobel on tue 12 dec 06
The Clayart archive has referencesto Reitz Green which is a lvely matt
colored with rutile and cobalt. It can be either blue or green depending on
application and atmosphere. the amount of rutile varies with the source of
the formula, but it is a 1-2% variable that produces good results..
good luck
Donald
David Hendley on tue 12 dec 06
There are two good avenues for experimentation on the road to
a good cone 10 reduction matt green glaze.
One, as you mentioned, is the cobalt-titanium (or rutile)
combination. The most well-know glaze of this type is Reitz
Green, as Hank replied. My recipe, by the way, calls for EPK
kaolin and I can think of no reason to use Grolleg kaolin. In fact,
Grolleg kaolin is usually specified for glazes which cannot stand
the addition of titanium, of which EPK contributes a small
amount. I also use spodumene instead of pedilite, and add a little
silica to approximate the pedilite.
Reitz green will be brown when applied too thin.
I also used Reitz green as the stepping point for my own cobalt
green glaze which is semi-glossy. It has a similar color, but Reitz
green is too matt for my tastes.
A second class of matt greens comes form an iron-calcium
combination. This is what is going on with your Shaner glaze
and ash glaze. It is very typical for matt ash glazes to go
green. I think the addition of copper is what makes the glaze
go purple - if you want green, you would be better off without
the copper.
As is typical of matt glazes, these types of glazes will also
usually be high clay glazes - a lot of alumina, and short on silica.
I use a slip glaze that is 60% Redart clay, plus calcium and
spodumene that is a nice matt green.
These types of glazes can turn out yellow or brown if applied
too thin.
So, the ever-so-simple starting point for your experiments is
to just leave the copper out of the glazes you list. There is also
no good reason I can think of for including tin oxide in a
green matt ash glaze.
I think it would be possible to formulate a matt cone 10
reduction glaze using copper, by really loading the glaze with
copper, but I wouldn't go down that path because of leaching
concerns, extra expense, and there are better ways to
achieve matt greens.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
>A friend of mine has been using Shaner's Green for a number of years has
> asked me for help in formulating a new glaze. Sometimes it is not green
> but
> purple (reduction at the right time!).
>
> When I run the Shaner's Green through glaze calculation software I note
> that it is short on Silica (which makes the amount of copper an issue).
> The
> recipe is provided below.
Snail Scott on tue 12 dec 06
At 09:36 PM 12/11/2006 -0500, you wrote:
>...named glazes for which there are no recipes (Pinnel's Stronium Matt
Green).
That one is normally called 'Weathered Bronze';
try a search for that. It's a light turquoise-
green, so it may not be quite what you need.
Does it need to be a copper green? How about an
iron green, or a chrome green, or a stain green?
-Snail
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