Lili Krakowski on tue 22 may 12
In the recent thread about zinc and boron glazes a couple of =3D
points--forgive me--were overlooked.
Zinc works as a flux only at 2% and below. After that the references =3D
tell us, it becomes refractory even an opacifier,(or why CM did, maybe =3D
still does, list Zinc apart from the body of a recipe. Zinc also does =3D
some other stuff specific to it.
Boron is not truly a flux. I know, I know, much disputation about =3D
whether A Flux actually is A Melting Agent. But--again check the =3D
authorities--Boron can be/is a glass former...To be very primitive when =3D
boron replaces alumina it will lower the maturation point of a glaze.
Zinc and boron together counteract copper blues. Lots of zinc--the =3D
books say--with titanium forms crystals. Is that so, Prof. Schran?
My point in all this is that when you use boron in a cone six glaze, and =
=3D
when you use zinc--the two are not true substitutes for each other the =3D
way
whiting plus silica substitutes for wollastonite, or magnesium carb and =3D
whiting can replace dolomite. =3D20
An analogy. If you are worried about burglars you can get a dog, or an =3D
alarm system. Either should keep burglars out. But a dog and an alarm =3D
system are not the same thing. Neither are boron and zinc...though they =
=3D
both can do the job.
And a plug once more for Michael Bailey's "Glazes cone 6". ISBN =3D
0-8122-1782-9 A &C Black, University of Penn.
It is a wonderful book and all us mid-temp firers should own it, just as =
=3D
much as we own RonJohn's book. Bailey uses zinc consistently, and gets
some gorgeous glazes.
And no: I do not know Mr Bailey, am not related to him, no financial =3D
interest etc etc. Poor me!
Lili Krakowski
Be of good courage
William & Susan Schran User on tue 22 may 12
On 5/22/12 10:20 AM, "Lili Krakowski" wrote:
>Zinc and boron together counteract copper blues. Lots of zinc--the books
>say--with titanium forms crystals. Is that so, Prof. Schran?
It is so, but it is zinc and silica that form the zinc silicate macro
crystals. Titanium is often added to "seed" the crystals, but titanium can
also form crystals without the zinc.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
douglas fur on tue 22 may 12
L-
I'm concerned for your claim to pedantry-
you state without a quibble of a qualifier
"whiting plus silica substitutes for wollastonite, or magnesium carb and
whiting can replace dolomite."
What about the synergy of oxides co-mingled in minerals as opposed to those
from carbonates in kraftpaper bags? (I'm not alluding to those tied up with
string)
Be of good courage
DRB
Seola Creek
Lili Krakowski on wed 23 may 12
Douglas writes that " [I] state without a quibble of a qualifier =3D
whiting plus silica substitutes for wollastonite, or magnesium carb and =3D
whiting can replace dolomite." What about the synergy of oxides =3D
co-mingled in minerals as opposed to those from carbonates in kraftpaper =
=3D
bags? (I'm not alluding to those tied up with string)."
There is a here, and there is a there. It is well known that mined =3D
materials will vary from mine run to mine run, country of origin to =3D
country of origin (vide recent discussion of spodumene) and that mined, =
=3D
natural materials will contain traces of this and that not included then =
=3D
in glaze calculations. =3D20
So I think it safe to say that were you to run out of wollastonite but =3D
have whiting and silica you could recalculate and test the substation. =3D
And this will work in most cases. As I always nag never to put a glaze =3D
on good pots without having tested that particular new mix, esp. if =3D
there are materials
in it just came from the supplier--which might from be a different mine =
=3D
run, country--see above--I have a very clear conscience on the topic. =3D20
As to oxides and carbonates..the literature does deal with that. =3D20
As to string and paper bags! That is a big topic and we may need a =3D
special discussion group to handle it..
ivor and olive lewis on wed 23 may 12
Dear Lili Krakowski,
Whiting and Silica may substitute for Wollastonite. Whiting plus Alumina
plus Quartz may substitute for Anorthite. Could Quartz substitute for
Tridymite ?. Perhaps. But if you use these raw unprocessed materials in the
proportions recommended by Michael Cardew the mixture you make will not fus=
e
as be predicted at cone 6, to cool and solidify into a vitrified mass that
would substitute for a glaze.
Most of the Zinc Crystalline glazes I have seen and illustrations in books
suggest that the macro crystals are opaque and the intervening glaze is
coloured and transparent. It has also been extremely fluid. Such recipes
can contain in excess of 25% Zinc oxide.
Text books have yet to give me an adequate definition of the term "Flux". S=
o
when I read "Zinc works as a flux only at 2% and below" I wonder what is it=
s
function, What is it contributing ?. If I read Frank Hamer correctly, Zinc
oxide changes the Viscosity of the vitrified fluid, making it flow with
greater freedom. It will also increase Surface Tension of the molten mass.
The wonderful thing about those two glass formers, Silicon dioxide (Mp.1610
deg C) and Boric trioxide (Mp. 460 deg C) is that in the molten state they
do not mix and form a uniform solution. They are immiscible and separate on
cooling to give an opalescent glaze popularly known as "Floating Blue" . I=
n
reality these oxides are not used. Borate minerals melt in the region of
1100 deg.C., Silicate minerals at slightly to significantly higher
temperatures.
I wonder, can our current Clayart Membership invent plausible, logical,
factual natural histories for each of the various classes of glazes withou=
t
repeating what was published in the twentieth century.
Sincere Regards,
Ivor Lewis,
REDHILL,
South Australia
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