Taylor Hendrix on thu 8 jan 04
Howdy all:
I=92ve been doing some reading in preparation for tomorrow: going to Austin
to buy my glaze materials. I have collected several articles, emails, etc
regarding my firing range (^4.5.6) and came across an old Val Cushing
article from _The Studio Potter_.
=93Firing in Oxidation to C/4.5.6=94 vol.5, no.2 (June 1977).
I am looking at different recipes to get an idea of how different glazes
go about doing what they do, and I have some questions about the glazes in
Cushing=92s article. I will post the recipes below. First the questions.
Many of the recipes use barium carb. In my reading, barium carbonate
(okay barium ox) is described as a refractive flux and used mainly for
producing matts (drr, barium matts). Most of the glazes below have 10%
barium carb. One has almost 25%. Why such a drastic difference? Will
10% not give much of a matt effect at C4.5.6?
Also, these glazes do use whiting. I have also noticed that many of
Barb=92s glazes (^6) also use whiting to source the Ca. Some of you have
suggested to me (by the way, thank you all for the help) to source Ca from
something other than whiting. I will be getting both whiting and ...
er... I forgot what else to source the Ca. Is it just a preference here
in these glazes? Don=92t worry, I=92ll test.
Is the lithium carbonate, when present below, only used to offset an
expansion problem?
Many of these glazes use barium carbonate, one uses lithium carbonate, and
one cryolite, so I will not be using any of them for starting points, but
I am finding it interesting to look at these old timers.
1=97C/5.6 Stone Matt, Whitish Base
Neph sy 50
Barium carb 10
F#3124 5
Whiting 5
Lithium carb 5
E.P.K. 10
Flint 15
---------------------
100
2=97C/5.6 Albany Slip Glaze
Albany slip 72 (so sad, all gone yum)
Barium carb 10
Cryolite 6
Gerstley 12
---------------------
100
3=97C/5.6 Alkaline Matt
Neph sy 30
F#3110 25 (High Alkali Leadless Body Flux)
Barium carb 10
Whiting 15
E.P.K. 10
Flint 10
---------------------
100
4=97C/5.6 =93Weird=94 Matt, Speckled (I=92m going to fox feed on this one)
Gerstley 50
Talk 35
Rutile 15
---------------------
100
5=97C/4.5.6 Leadless, Glossy Transparent
Kona F-4 35
Gerstley 23
Barium carb 8
Whiting 8
E.P.K. 8
Flint 8
---------------------
100
6=97C/5.6 Barium Stone Matt
Neph sy 60
Barium carb 24
Lithium carb 5
E.P.K. 6
Flint 5
---------------------
100
If you want to make any comments about these glazes, feel free. They are
Cushing=92s not mine. He had three more recipes in the article. I didn=92t=
have a question about their ingredients.
Going to be a fun ride, folks! Yee haw. Once again thanks to the several
people who commented to me on and off the list regarding my first baby
steps. Love Claytown.
Taylor, in Waco
piedpotterhamelin@COMCAST.NET on fri 9 jan 04
HI
The Barium issue is one of toxicity. While I don't use barium, I do remember that some sort of limits were issued or advised years ago due to barium leaching. I vaguely remember that amounts above 6 or 8 percent were to be avoided. Barium is rat poison
Lithium can improve glaze fit but in larger amounts it will promote a matt surface.
Have a fun ride
Rick
--
"Many a wiser men than I hath
gone to pot." 1649
Krista Peterson on sat 10 jan 04
>Many of the recipes use barium carb. In my reading, barium carbonate
>(okay barium ox) is described as a refractive flux and used mainly for
>producing matts (drr, barium matts). Most of the glazes below have 10%
>barium carb. One has almost 25%. Why such a drastic difference? Will
>10% not give much of a matt effect at C4.5.6?
You could test the glaze with 25% barium by using 10% instead and see what happens. Also, I've heard that 4% barium carb is the limit for toxicity. But I have used Strontium carb in place of Barium and gotten the same results. I have heard that you're supposed to replace the barium with strontium by 75%, that is if you have 10% barium you would use 7.5% strontium. But I have replaced it straight across and gotten the same results. I spose it depends on the glaze. If you are making functional work intended for use I would just avoid barium carb, there's plenty of nice glazes out there without it. I don't think strontium carb is toxic, having said that I guess we'll find out soon enough.
I had a great teacher for my glaze research and she always said when you test glazes to find out what a particular component contributes to the glaze, that you should only change 1 thing in the glaze, otherwise you don't know which change produced the change.
Happy testing!
Krista Peterson
lili krakowski on sat 10 jan 04
Dear Taylor:
I thought of sending this directly, off list, so as not to make it sound =
like I'm picking on you, which I would not dream of doing, as you are =
not only a clay pal, but a pen pal.
You are setting up as a glaze maker-- a task never completed, a task =
that last all one's life. And you send us the recipes for a number few =
glazes you mean to try.
Let us look at them (Yesterday, even, I'd have written my usual =
"lettuce" But fellow old lady (I am older! nyah,nyah, nyah!) =
reprimanded us...)
The first; BaO .166
Li02 .219
Na20 .276
K20 .083
MgO .006
CaO .250
Al203 .511
B203 .032
Fe203 .002
SiO2 2.83O
Ok. This glaze has about as much earths (Barium, calcium, magnesium) =
as alkalines ( lithium, Soda, potash) A traced of boron.(I am skipping =
the AL/Si2 ratio here. You have one toxic material, that as you know =
from my previous rants, makes your studio a dangerous place, and some =
lithium about which the jury is out, but which you DO NOT want around if =
you are going to take in pupils.
The second is an Albany slip glaze, to which I will return.
The next goes like this:
BaO .374
LiO2 .206
Na2O .292
K20 .091
CaO .032
Al203 .490
Si02 2.250
It looks almost as though the originator had replaced calcium with =
barium. Again I am leaving the ratio of alumina to silica out
I will skip the next glaze, which TGSF is barium free.
And we have
BaO .144
N20 .177
K20 .065
MgO .003
CaO ..611
=20
Al203 .401
B203 ,303
SiO 2 2.343
And here essentially you have replaced some barium with calcium.
The other glaze is interesting.
Na20 .050
Mg0 .514
CaO .436
Al203 .070
B203 .364
Si02 .989
TiO .353
I have no idea where this glaze plans to go! I mean this a bit =
literally (though I may mean litterally, as I suspect it will litter the =
kiln shelf) =20
Ok. What I wonder is--what will you learn from these glazes? You are =
changing several ingredients at once, and I do not see a consistent =
progress.
If I could advise you I would suggest you try Robin Hopper's flux =
exchange idea; where he has a glaze and then substitutes just one, only =
one ingredient at a time. I do not seem to locate the recipe, but =
someone else, someone who already owns the book, probably can tell you.=20
But right now it seems to me that testing glazes at random without =
follow through--what does this material do, what does that, will prove =
costly in time and materials and fruitless.
You might even be better off taking one of these--maybe #3--and doing =
straight line blends, replacing the barium with zinc, for instance, or =
with magnesium, or with strontium. Then a triaxial of the best.....
David Hendley on sat 10 jan 04
Dear Taylor, I think maybe Cushing used to own stock in the company
that made barium carbonate. I can see no good reason for its
ubiquitous inclusion in every recipe.
It is indeed a 'refractory flux' even at cone 10. At cone 4 it would
do even less melting.
To me, it would make more sense to forget the barium, replace it
with calcium, and add some more clay to make the mix more matt.
This would provide the following advantages:
1. More clay in the glaze slop for better suspension and application.
2. No dangerous materials to poison the user of the finished pottery
if the glaze is not stable, or the potter even if it is.
3. Whiting is on the order of 1/10 th the price of barium carbonate.
If you agree with me, you have two choices: try to adjust these recipes
and test several test variations, or just find a whole new group of
recipes to start with.
It would, of course, be very helpful to know how to do glaze calculation
if you want to adjust the recipes, but the 'educated guess in the dark'
method would probably yield some good results as well.
The other common sources for whiting are
1. Feldspar, but whiting is a minor component, so it would never be
a substitute for whiting.
2. Dolomite, which is calcium and magnesium. This would be a good
choice if a recipe calls for whiting and magnesium carbonate or
whiting and talc.
3. Wollastonite, which is calcium and silica. This probably the one you
were thinking of, because most glaze recipes use whiting and flint
(silica), and wollastonite can be used to replace some or all of
each.
Some people recommend using wollastonite because it has less material
that burns away (the carbonate in calcium carbonate, or whiting), which
means less of a chance the glaze will develop blisters from violent
bubbling during the melting phase.
I don't know why lithium carbonate is used in one of the recipes. It
could be to lower the expansion or it could be to affect the fired
character of the glaze. I would try it without the lithium and see if
it's just as good without it (replace it with another flux).
If you want to try any Albany Slip-based recipes, remember that you
can use my Redart clay-based Albany substitute just like the real
thing. In most cases the results are identical.
Redart Clay 72
EPK 5
Talc 5
Soda feldspar 8
Whiting 10
Total 100
Mix well and put in your "Albany Slip" container. When a recipe calls for
Albany, weigh and add the same amount of this.
Have you considered going to Dallas for materials?
Where did you find 25-year-old Studio Potter? The Studio Potter
magazines from the late 70's and early 80's are pure gold.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
I've been doing some reading in preparation for tomorrow: going to Austin
to buy my glaze materials. I have collected several articles, emails, etc
regarding my firing range (^4.5.6) and came across an old Val Cushing
article from _The Studio Potter_.
"Firing in Oxidation to C/4.5.6" vol.5, no.2 (June 1977).
Ababi on sun 11 jan 04
Hello David
When Val Cushing wrote his book "BARIUM" was not known - probably -as a
"bad" poison - as we know it today. It can be replaced by whiting as you
said or even better by0.75 of the amount into strontium carbonate.
The only case I found it unchangeable is with the barium purple- so I
will not have that purple!
The lithium in many cases can be replaced through software into spodumen
which is a more stable source of Lithium Oxide.
I do agree with you and I succeeded at least in two lithium recipes to
remove it completely and still having the same beautiful glaze as I had
had before.
The last sentence: Thank you for your Albany slip sub - it helps me in
my tests...
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://ababi.active.co.il
http://www.matrix2000.co.nz/Matrix%20Demo/Ababi.htm
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of David
Hendley
Sent: Sunday, January 11, 2004 1:05 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Putting the question to the glaze
Dear Taylor, I think maybe Cushing used to own stock in the company
that made barium carbonate. I can see no good reason for its
ubiquitous inclusion in every recipe.
It is indeed a 'refractory flux' even at cone 10. At cone 4 it would
do even less melting.
To me, it would make more sense to forget the barium, replace it
with calcium, and add some more clay to make the mix more matt.
This would provide the following advantages:
1. More clay in the glaze slop for better suspension and application.
2. No dangerous materials to poison the user of the finished pottery
if the glaze is not stable, or the potter even if it is.
3. Whiting is on the order of 1/10 th the price of barium carbonate.
If you agree with me, you have two choices: try to adjust these recipes
and test several test variations, or just find a whole new group of
recipes to start with.
It would, of course, be very helpful to know how to do glaze calculation
if you want to adjust the recipes, but the 'educated guess in the dark'
method would probably yield some good results as well.
The other common sources for whiting are
1. Feldspar, but whiting is a minor component, so it would never be
a substitute for whiting.
2. Dolomite, which is calcium and magnesium. This would be a good
choice if a recipe calls for whiting and magnesium carbonate or
whiting and talc.
3. Wollastonite, which is calcium and silica. This probably the one you
were thinking of, because most glaze recipes use whiting and flint
(silica), and wollastonite can be used to replace some or all of
each.
Some people recommend using wollastonite because it has less material
that burns away (the carbonate in calcium carbonate, or whiting), which
means less of a chance the glaze will develop blisters from violent
bubbling during the melting phase.
I don't know why lithium carbonate is used in one of the recipes. It
could be to lower the expansion or it could be to affect the fired
character of the glaze. I would try it without the lithium and see if
it's just as good without it (replace it with another flux).
If you want to try any Albany Slip-based recipes, remember that you
can use my Redart clay-based Albany substitute just like the real
thing. In most cases the results are identical.
Redart Clay 72
EPK 5
Talc 5
Soda feldspar 8
Whiting 10
Total 100
Mix well and put in your "Albany Slip" container. When a recipe calls
for
Albany, weigh and add the same amount of this.
Have you considered going to Dallas for materials?
Where did you find 25-year-old Studio Potter? The Studio Potter
magazines from the late 70's and early 80's are pure gold.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
I've been doing some reading in preparation for tomorrow: going to
Austin
to buy my glaze materials. I have collected several articles, emails,
etc
regarding my firing range (^4.5.6) and came across an old Val Cushing
article from _The Studio Potter_.
"Firing in Oxidation to C/4.5.6" vol.5, no.2 (June 1977).
.
Hendrix, Taylor J on mon 12 jan 04
Have no fear fair Lili. My interest in the Cushing glazes was mere
academic. I was wondering how so many glazes could have barium
carbonate, a material I know to be yucky bad. Not a gram of barium carb
has crossed my threshold on my word. As for my own tests. I will be as
methodical as Dr. Frankenstein if somewhat more conservative in my
energy usage.
Wish me luck!
Taylor, in Waco
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of lili
krakowski
Sent: Saturday, January 10, 2004 4:36 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Putting the question to the glaze
Dear Taylor:
I thought of sending this directly, off list, so as not to make it sound
like I'm picking on you, which I would not dream of doing, as you are
not only a clay pal, but a pen pal.
You are setting up as a glaze maker-- a task never completed, a task
that last all one's life. And you send us the recipes for a number few
glazes you mean to try.
...
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