Lili Krakowski on tue 9 may 06
ABOUT RECIPES: PART II
Recipes are made up in different ways. I think the two prime sources are
other recipes adjusted at need or desire, and experiments that start out
with an idea, and end up as a glaze. Simply put, the same glaze can be ma=
de
up with different materials. (Explained in The Basic Internet Glaze Cours=
e,
to be found in the Archives for Week 3 of April 2005)
Several different recipes may represent just one glaze.
My first example comes off an ancient list (still typed on a manual
typewriter!) and the source was one Bob Anderson. This glaze is
described as a MIX OF THREE EXISTING GLAZES. The author says it
probably can be simplified, but he is reluctant to do so, as it is so nic=
e
the way it is.
Here goes:
Recipe Name: BLACK
Albany Slip 29
Custer spar 38
Barium Carbonate 3.9
Whiting 2.1
Gerstley Borate 8.1
Zinc Oxide 2
Wollastonite 4
Nepheline Syenite 3
Flint 1.6
Ball Clay 8.8
Additives
1.6 Copper Carbonate
.06 Copper Oxide--Black
1.6 Manganese Dioxide
2.3 Cobalt Oxide
0.088 Iron Oxide--Black
The source of the recipe did not want to monkey with it.
We have no choice, as Gerstley borate and Albany Slip are =93gone.=94
And we no longer use barium.
Here we have two options: to do it by well-informed guess-work, or to
calculate. I can tell you right now we will get very similar results.
We take out barium and replace it with whiting. Gram for gram.
They have just about the same fluxing power. We could replace the barium
with strontium, if we were interested in a "barium blue", but with all th=
ese
colorants, and the goal of a black glaze, it is not worth the extra cost.
NOTE: I AM OMITTING COLORANTS IN THESE TESTS . Two reasons. I never test
with colorants because they often make glaze defects harder to detect, an=
d
because it makes visual comparison with glazes I already have more
difficult. Of course, with Red Art in the recipes, these glazes won't be
white.
FIRST VARIATION: Gerstley Borate has a relationship of 1 part
calcium to 1.5 Boron. Frit 3195 comes close, but I will use less of it in=
my
first test for fear of over-fluxing. I drop the small amount of Neph. Sy,
because Frit 3195 gives me soda. Neph Sy also gave more alumina and silic=
a
than the frit. I ignore that for now. I am getting less boron here, and t=
he
amount of other ingredients also is different, so this is an =93educated =
stab
in the semi-dark=93.
I know Albany Slip had more magnesium in it than Red Art does, and
this would affect the glaze. And it had more calcium. So I replace the
Wollastonite with Dolomite. And I know that Red Art has more silica
and alumina than Albany Slip so I lower my clay.
REVISED BLACK I
Red Art 29
Custer Spar 38
Whiting 6
Frit 3195 6
Dolomite 5
Flint 3
Ball Clay 4
Zinc 2
And
I will test with Frit 3124, which has less boron and alumina than 3195.
REVISED BLACK II
Red Art 29
Custer Spar 38
Whiting 6
Wollastonite 5
Dolomite 5
Frit 3124 3
Zinc 2
Flint 3
I am not really happy with this, because it is a niggling change. I will
drop whiting and flint and add to the Wollastonite.
REVISED BLACK THREE
Red Art 29
Custer Spar 38
Wollastonite 10
Dolomite 5
Frit 3124 3
Zinc 2
I like the last best as it has few ingredients and they are in manageable
quantities.
I could make up a few recipes using other frits. But the two I chose are
very commonly used, and will do to make my point.
Now I go ahead and test. As I cannot test the original-- no Albany Slip, =
no
Gerstley Borate, no barium-- I am testing in the dark. Be advised: no mat=
ter
where you get a recipe, whether as recipe or formula, you NEED TO TEST.
I went to my Glaze Master (=99 ) program and figured out what my revision=
s had
accomplished. Had I not had this program I would have done it with a
calculator.
CALCULATED REVISION
Red Art 55
Neph.Sy 16.6
Dolomite 2
Frit 3124 15
ZnO 1.5
Whiting 5
The formula is given with the others.
Only the Calculated Revision has the same amount of Boron as the Original=
.
My revisions were quite close to the original in the balance of sodium,
potash, calcium and magnesium.
This is how it all looks on a chart:
Original ___Rev. I ___Rev. II____Rev. III____Calculated
NA2O ___.117 _____.103 _____.087 ______.089_______ .185
K2O ____.187 _____..219 _____.193 ____. 212 ________.144
MgO____.124 _____.155 _____.142______.162._______ .140
CaO ____.416_____.425______495_______.453________.449
BaO _____.70_______ X_______ X _________X_________X
ZnO ____. 085 _____.098_____.089 ______.084_______ .082
Al2O3___ .468 _____.526_____ .415 ______.457 _______.616
B2O3_____.129 ____ .083 _____.021______ .023_______ .129
Fe2O3 ____.058____ .055_____ .049 ______.053________.106
SiO2 _____3.288____ 3.586___ 3.133______ 3.414______ 3.907
Looking at these, prior to testing, I see that Revisions I and
II, and III have less boron than the original. There are differences
in alumina, boron and silica contents as well between Original and=20
Revisions..
This might affect maturity, and the look of the surface.
If the test results did not appeal to me--and remember, here, I never saw
the original--I would revise my Revisions! And, of course, colorants ca=
n
act as fluxes or as refractories, again with effects on surface. It proba=
bly
will take several tests of these revisions to achieve a result that pleas=
es
me.
HOW COME THE CALCULATED GLAZE DOES NOT DO BETTER
THAN THE "GUESSED AT" ONES?
Because I had/have a limited number of frits available! I could have gon=
e
through all possible existing frits, but I do not have them.
Yes, I could order some, but at this point it is not worth the expense,
and the storage space. And this is something to keep in mind. One cannot =
own
every material. In a school situation it is desirableto have a small
quantity of " everything" on hand. In a studio one is forced to limit
oneself to the reasonable.
What now?
Here we already have four possible revisions of this Basic Black.
Meanwhile someone might be testing it with Ravenscrag or Alberta, or
Fremington Clay-- a clay often listed as an Albany substitute in
British books. And someone might have a larger/different selection of fr=
its=20
on
hand . So, we could have not 4 but 12, 16, even more variations.
This example indicates how a perfectly "normal" glazes can develop
when the unavailability (Albany Slip, Gerstley Borate), or undesirabilit=
y
(Barium) of an original material
forces a change in the recipe. From this single given, many recipes can
result. Not to mention that someone along the way might have to make furt=
her
changes if the recipe she got crazed on her clay.
So what happens next?
FOR THIS WE GO TO PART III.
Lili Krakowski
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