Craig Martell on mon 14 jul 97
Hi, I'm back!
Thanks to Jeff Lawrence for enlightening me as to the potential problems in
regard to Gerstley Borate or Greasy Buttache or whatever you want to call
that stuff. I've been using "K" grind Gerstley Borate from Industrial
Minerals in San Carlos. Calif. for a long time. I don't use a lot so I've
had the same lot for centuries. It must have been processed and selected
well because I don't have trouble. I hope that the "K" as in grind, doesn't
stand for "kinda".
As penance, I've recalculated the Berry Rust glaze with a frit. The seger
formula is almost identical to the original. The silica was too low, so I
took it up to the lower end of the suggested limit. I make no claims as to
the aesthetic properties of this glaze, ie., test it!! Jeez, where is Ron
anyway? He's supposed to do this stuff!
Recalculated Berry Rust cone 10 ox
=================
SILICA.............. 25.13
EPK KAOLIN.......... 22.69
NEPHELINE SYENITE... 8.61
FERRO FRIT 3134..... 19.93
BONE ASH............ 8.97
TALC................ 14.67
RED IRON OXIDE...... 8.59
========
108.59
CaO 0.49* 8.55%
MgO 0.36* 4.51%
K2O 0.02* 0.46%
Na2O 0.14* 2.79%
Fe2O3 0.17 8.32%
TiO2 0.00 0.06%
P2O5 0.09 3.92%
B2O3 0.20 4.37%
Al2O3 0.32 10.12%
SiO2 3.01 56.90%
Cost/kg 0.79
Si:Al 9.54
SiB:Al 10.17
Expan 6.43
This glaze is a bit more expensive than the original formula which is
$.63/Kg, probably due to the frit addition. Also, I used Insight 5.0 to
recalculate. It's a good progaram and is very easy to use. When I get a
minute, I think I'll test the two formulas and will post my results.
Regards, Craig Martell-Oregon
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