Tom Buck on tue 7 may 02
June Perry:
I did the "rationalization" of GB for Tony some years back; the
stuff is a rock that is a mixture of minerals, chief of which are two:
ulexite (Na/Ca/B oxides) and colemanite (Ca/B oxides) both minerals being
hydrated to a degree. But almong with the U & C are gangue materials,
chiefly Ca/Mg carbonates, and shale (fossilized clay).
the GB analysis kept changing with time, and when the B2O3 content
was consistently below 25%w US Borax quit mining the rock because its
customers wanted a material higher in B2O3.
There always was some MgCO3 present in the rock; it was often
ignored in analytical procedures, so sometimes it was given, other times
not offered.
FYI, here are analyses supplied by Hammill & Gillespie over the
years, which I cited to a Czech potter a year or two ago:
J-M:
Here are the analyses you wanted:
Nepheline Syenite Canada (weight percent)
60.7 SiO2; 23.3 Al2O3; 0.07 Fe2O3; 4.6 K2O; 9.8 Na2O;
0.7 CaO; 0.1 MgO; 0.7 LOI.
Gerstley borate is complex... the grade has been
shifting steadily, and all I can do is give you the 1993,
1997, and 1999 levels in weight percent:
Gerstley Borate, as cited by Hamill & Gillespie:
as of 1993: 9.8 SiO2; 1.3 Al2O3; 0.35 Fe2O3; 0.14 K2O;
4.7 Na2O; 17.9 CaO; 3.5 MgO; 23.3 B2O3; 34.0 LOI.
as of Aug 97: 11.73 SiO2; 1.63 Al2O3; 0.48 Fe2O3; 1.38 K2O;
4.39 Na2O; 19.06 CaO; 4.10 MgO; 27.68 B2O3; 29.35 LOI,
as of May 1999: 21.2 SiO2; 7.0 Al2O3; 2.9 Na2O; 18.9 CaO;
25.7 B2O3; 22.5 LOI. (US Borax lab ignored MgO).
As you will see, you have to know when the glaze recipe first
was designed to know how to sub for the GB. Today's GB is
much more refractory than before.
Good tests. BFN. Tom.
------------
The only people really interested in GB's analysis are the Raku potters
who use formulas like 80GB;20 N.Sy. (a common popular mix). Rakuers get
upset when they fail to see the glaze mix melting at C012 (more or
less).
How's Florida working out? be well. Peace. Tom.
Tom Buck (User ID) and/or ("alias")
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
June Perry on tue 7 may 02
Ron, I ran frit 3124 through Tony Hansen program.and matched it (very
closely) empirically with the formula I posted. I just re-checked it and on
the Tony Hansen software, the recipes side to side, are empirically very,
very close.
Now either one of us is not understanding something or the program is doing
something screwy.
The formula I posted was not a substitute for her glaze recipe. It is only a
recipe to make up a batch of material to mix as substitute for Frit3124.
When I rechecked them side by side, both 100 of my frit 3123 sub and 100 of
frit 3124 show.55 moles of B2O3, .7 Cao, etc.
Tony's Gerstley borate formula does not show any mgo, which is why none is
in my substitute.
Gerstley Borate is more often shown as this which I just found, using a web
search
2Cao . 3B2O3 . 5H2O
This is the same formula that Rhodes gives in Clay and glazes. Parmalee, as
far as I could find in a quick search, only addresses Colemanite (same
formula as shown above for the gerstley).
I see that Tony on his web site of gerstley subs, lists gerstley borate
rationalized, which does includ Mgo, but it is not in the formula in his
software, nor in the source for the one I listed above. I don't know what it
means by rationalized. I know that gerstley has been somewhat inconsistent
in
it's formula over the years, so I'm assuming that at one time it had MgO in
it????
I'm certainly up to admitting a mistake if one was made and I'm certainly up
for improving my limited knowledge of glaze chemistry.
Warm regards,
June
June Perry on wed 8 may 02
Tom, thanks for those figures. I thought the same thing about the
gerstley --
first figure out what batch someone has and also, how old their recipe is!
I
had some old gerstley (probably from the 80's) that I sold before I left
Oregon and then got a few more bags when it was announced that the mining
operation was stopping. I wish I had saved some of it to do a side by side
melt of the old and the new. I still have a tiny bit of Colemanite. I think
I'll try a melt of that and the new gerstley. As soon as I get the time I'm
going to enter that newer analysis into my glaze software and call it
Gerstley New!!!
Gerstley is not the only material that changes with time, as you know,
although it's changes are probably more dramatic than others. Looking at
some
empirical formulas for Custer in the Rhodes books and later analysis shows
the alterations over time, which is one of the reason glaze recipes don't
travel well. It isn't just the local water. LOL
We're seeing that now with spodumene. People are complaining that their new
material isn't working for their glazes. This is where the glaze programs
come in handy if you can get the empirical formulas of the original recipe
or
the materials used at the time.
For those of you just getting into glaze formulation, know that you can get
a formula of current stock either through your local supplier, or the mining
company. It's good to keep these sheets so you can alter your recipe down
the
line, if needed.
Not everyone can afford the outlay to buy tons of a material, nor do they
have the where with all to store it, so it is a good idea to keep track of
your materials this way.
And Tom, life in Florida is glorious -- so much so that I find it hard to
get
in studio time! This past week was the first time I actually spent a full
day
in the studio. We've done a tremendous amount of work on the house and
studio
and I had over a half acre to landscape; and now we're getting ready to put
in a dock (permit is in the mail, we've been told!). Once we get our boat I
may be even more distracted from the studio! LOL Ah, the joys of retirement.
:-)
It's taken 9 months to get to this place, but it's been pleasant throughout.
We had great workers, the place is beautiful and the weather and living on
the water is glorious! Life couldn't be better. I wish the same for
everyone!
Time to close -- have some bowls to trim this morning before heading down to
Melbourne for chores and lunch.
Warmest regards,
June
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