Paul Lewing on fri 5 jan 01
Leslie,
I've had quite a bit of experience with these ^6 iron reds and I've
found out a few things about them. One thing I've found out is that if
you make them conform to limit formulas, they will not be red. The
color depends on having virtually no alumina. I noticed that the
reformulated version that John Hesselberth did for you had a Si:Al ratio
of about 10:1. My experience with these things is that they will not be
red with a ratio under 15.
My advice is to look at the web site www.gerstley borate.com, also
available through the digitalfire.com site. One of the hardest glazes
to duplicate with a GB substitute is this kind of iron red, and it's one
of the things the formulaters of Boraq, another GB substitute, are
particularly working on. In fact, there's a whole article on iron reds
there.
Happy testing.
Paul Lewing, Seattle
LESAINT1@AOL.COM on fri 5 jan 01
Hello everyone,
Of course my best iron red glaze has gerstley borate in it, and I'd really
like to keep this glaze after I run out of gerstley (which will be soon).
I'm having no luck in substitutions for gerstley borate. Here's the recipe:
Touchstone Red C6 ox
flint 30
gerstley borate 32
soda spar 20
talc 14
red iron oxide 15
kaolin 5
So far I've tried direct substitution of Murray's Borate, Laguna
Borate and frit 3134 for the gerstley. The Laguna and frit result in the
same surface appearance as the original glaze but an ugly brown color. The
Murray's looks the same as the original, but it splatters off the pot.
Does anyone have any suggestions on how to reformulate this without gerstley?
Thanks,
Leslie St. Clair
Ft. Mitchell, KY
Steve Burtt on fri 5 jan 01
Hi Leslie,
I have a simple recipe for iron red and I have substituted Laguna Borate
for the Gerstley with success. However, the application must be a heavy one
to keep from getting the ugly brown. Here's my cone 6 recipe:
Gerstley (subbed with Laguna Borate) 55
Talc 15
Flint 30
Red Iron Oxide 22
Here's another that has proven successful, but I haven't made the
substitution yet. I'm planning to try it with Laguna Borate, too. Again, this
is a cone 6 and requires heavy application:
Randy's Red
Gerstley 31.69
Talc 13.86
Kona Feldspar 19.80
EPK 4.95
Flint 29.70
Red Iron oxide 15
Sorry about those decimals. I always round off because my scale is
nowhere near that accurate.
Hope this helps.
Steve Burtt
Ocean Springs, Mississippi
John Hesselberth on fri 5 jan 01
LESAINT1@aol.com wrote:
>Hello everyone,
>
> Of course my best iron red glaze has gerstley borate in it, and I'd really
>like to keep this glaze after I run out of gerstley (which will be soon).
>I'm having no luck in substitutions for gerstley borate. Here's the recipe:
>
>Touchstone Red C6 ox
>
>flint 30
>gerstley borate 32
>soda spar 20
>talc 14
>red iron oxide 15
>kaolin 5
>
> So far I've tried direct substitution of Murray's Borate, Laguna
>Borate and frit 3134 for the gerstley. The Laguna and frit result in the
>same surface appearance as the original glaze but an ugly brown color. The
>Murray's looks the same as the original, but it splatters off the pot.
>
>Does anyone have any suggestions on how to reformulate this without gerstley?
Hi Leslie,
You might try the glaze that follows. I left all the unity numbers
pretty much the same except I took the liberty of raising alumina up to a
level that should make this glaze fairly stable. The original was quite
low on alumina. If you decide to try it let me know if it works. With
the variability of gerstley borate it is pretty much a crap shoot as to
whether or not your glaze can be matched by this procedure. It really
depends on whether your GB is close to what I assumed it to be. I used
the 9/97 analysis. Also it doesn't have much clay. You may have to add
2% bentonite to get it to stay in suspension.
Regards, John
------
Glaze name: Touchstone Red (GB free)
Cone: 6
Recipe: Percent
Frit 3195 40.00
F-4 Feldspar 13.00
Talc 18.00
EPK 6.00
Wollastonite 5.00
Silica 18.00
Totals: 100.00 %
Add
Red Iron Oxide 15
Possible Health Hazards:
Talc: wear a NIOSH approved dust mask when handling dry material
Silica: free silica-wear a NIOSH approved dust mask when handling dry
material
Unity Formula for Touchstone Red (GB free):
0.020 K2O 0.277 Al2O3 2.934 SiO2
0.159 Na2O 0.390 B2O3 10.6:1 Si:Al Ratio
0.425 CaO
0.396 MgO
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
John Hesselberth on sat 6 jan 01
Paul Lewing wrote:
Hi Paul,
Now you have me intrigued. If it really is a ratio of >15 (vs. an
absolute low level of alumina required) I think I can test that. This
Touchstone Red glaze has enough boron in it that it still should melt
pretty well at ^6 with a silica level of 4.5. I've modified the recipe
to that level (ratio is 16.1 with all other unity numbers essentially the
same) by adding silica and I'll give both of them a try. Of course they
may shiver right off the clay because the expansion is so low, but it
ought to test the ratio theory. I've also made a second version with a
little more sodium and boron to make sure I get it melted. I'll post the
results in a couple days.
John
>Leslie,
>I've had quite a bit of experience with these ^6 iron reds and I've
>found out a few things about them. One thing I've found out is that if
>you make them conform to limit formulas, they will not be red. The
>color depends on having virtually no alumina. I noticed that the
>reformulated version that John Hesselberth did for you had a Si:Al ratio
>of about 10:1. My experience with these things is that they will not be
>red with a ratio under 15.
>My advice is to look at the web site www.gerstley borate.com, also
>available through the digitalfire.com site. One of the hardest glazes
>to duplicate with a GB substitute is this kind of iron red, and it's one
>of the things the formulaters of Boraq, another GB substitute, are
>particularly working on. In fact, there's a whole article on iron reds
>there.
>Happy testing.
>Paul Lewing, Seattle
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
Paul Lewing on sat 6 jan 01
Hi, John.
The ratio thing in the iron reds was not an issue of the glaze surface,
just the color. When the ratio got below about 15, the surface didn't
really change much, it just wasn't red any more. Actually, I gave up on
these GB iron reds bacause they were just too unpredictable. I never
found one that worked consistently enough for me, but I did find out
some things.
First, the kind of iron you use made a huge difference. The brighter
orange it was before firing, the brighter the red was after. Second,
bone ash made it brighter, and so did tin oxide, so did a little lead.
Titanium may have also, but not rutile. And how it was applied and
fired seemed to have a big influence.
What I really want is a real bright terra cotta orange color in a shiny
glaze with some texture to it. I thought I had one, but it seems to be
too unpredictable too. It's also 65% lead bisilicate. As the French
say, "C'est la fucking vie".
Let me know the results of your ratio tests. Just be sure to get all
the tests the same thickness and fire them all right together.
Later, Paul
LESAINT1@AOL.COM on sun 7 jan 01
Hi Steve, Thanks very much for your help with my question. I'll try both of
your recipes, and maybe apply my own tests thicker and see if that ugly brown
improves. I'll be posting my results.
Thanks again for your help.
Leslie
MaryBeth Bishop on sun 7 jan 01
Leslie,
Did you add bentonite to the test with Murray's Borate?
Mary Beth
LESAINT1@AOL.COM on mon 8 jan 01
Mary Beth, no I didn't add bentonite to the Murray's borate test. I just did
a straight substitution. Do you think it would help?
Leslie
Cindy Strnad on mon 8 jan 01
Leslie,
You probably already know this, but also try refiring that ugly brown in
your next bisque load and see what happens.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
John Hesselberth on tue 9 jan 01
Hi Leslie and Paul,
Well I learned that Paul is right about this type of glaze. It is not
straight forward. I made a little progress, but didn't make any big
breakthroughs.
First I was able to reproduce the GB-based glaze and get something pretty
darn close to a nice bright mottled terra cotta. On porcelain it was on
the yellow side; on stoneware it was pretty close to a bright terra cotta.
The recipe I suggested the other day, with the 10:1 Si/Al ratio was kind
of a yellowish green floating over brown--not exactly what I was looking
for. Don't bother to pursue it, Leslie.
I tried two different recipes with Si/Al ratios of 15-16. For the first
of those I simply increased the silica level in the glaze above until it
was 15. It gave a speckled black/tan on porcelain and a dark terra cotta
on stoneware where it was thick (dark brown where thin). The second
attempt I added some sodium and boron to try to get even better melting.
The samples were similar to those described directly above; although
there was a small patch on the stoneware sample, where the glaze was
thickest, that came very close to matching the GB original. That recipe
is below if anyone wants to continue to work with it.
Overall it seems that glaze thickness is important. I also got quite
different results between porcelain and stoneware with stoneware coming
closer to giving the color I was after. I think the chemistry needed is
not far from what is in the recipe below, but the physics are off. In
other words, there is something in the melting characteristics or the
viscosity vs. temperature profile that is not letting the iron red
crystals form the same way they do in the GB original. I also limited
myself to working within the framework of a stable glaze, as I understand
those criteria. It could be that alumina level has to be low on an
absolute level to make this one work. I may work on it a little more as
time permits; if anyone else solves the riddle please let us know.
Touchstone Red III (my best attempt at making it GB-free which wasn't
very close)
Cone 6 oxidation
Recipe: Percent
Frit 3195 33.00
F-4 Feldspar 15.00
Talc 13.00
EPK 1.00
Wollastonite 3.00
Silica 35.00
Totals: 100.00 %
Also add:
Red Iron Oxide 15.00
Bentonite 2.00
Possible Health Hazards:
Talc: wear a NIOSH approved dust mask when handling dry material
Silica: free silica-wear a NIOSH approved dust mask when handling dry
material
Unity Formula
0.030 K2O 0.270 Al2O3 4.311 SiO2
0.189 Na2O 0.415 B2O3 16.0:1 Si:Al Ratio
0.415 CaO
0.367 MgO
Regards, John
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
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