Craig Martell on thu 24 jul 97
Hi Debbie, Corinne, Lesley, and the rest o'you guys:
I just had a look at the Berry Rust glaze tests, the original formula, and
the recalculated fritted formula. They were fired to cone 10 Ox. buy my
wife, Linda Owen, in her trusty Skutt Kiln. Thanx Linda!
The two glazes are nearly identical. I didn't expect that, but ya never
know. The original formula with gerstley borate has more
calcium-borate-iron crystals floating in the matrix but you really can't see
this without a hand lens. A customer who has purchased pots with the
original formula would be hard pressed to tell the difference. I feel like
I've just taken the Pepsi Challenge!!
The tests were fired on porcelain. Four tiles were made of each glaze,
eight in all and the separate formulas were fired side by side in the top,
middle, and bottom of the kiln. No significant differences were seen. I
might also mention that I used English Bone Ash, and not Tri-Calcium Phos.
All the tiles were inspected with a hand lens and no crazing was evident in
either formula.
A separate set has been fired to cone 10 R but won't be available until
tomorrow. That's about it for now, e-mail me or post to clayart if I've
forgotten to mention anythin, and I probably have...it's my hobby! The
formulas and receipes are posted below. Happy testing,.....Craig Martell-Oregon
Berry Rust
==========
SILICA.............. 27.70 25.29%
EPK KAOLIN.......... 18.18 16.60%
NEPHELINE SYENITE... 18.18 16.60%
DOLOMITE............ 9.09 8.30%
GERSTLEY BORATE..... 9.09 8.30%
TALC................ 9.09 8.30%
BONE ASH............ 9.09 8.30%
RED IRON OXIDE...... 9.09 8.30%
========
109.51
CaO 0.49* 9.37%
MgO 0.36* 4.92%
K2O 0.03* 0.90%
Na2O 0.12* 2.64%
Fe2O3 0.17 9.17%
TiO2 0.00 0.05%
P2O5 0.09 4.15%
B2O3 0.20 4.73%
Al2O3 0.32 11.14%
SiO2 2.58 52.92%
Cost/kg 0.63
Si:Al 8.06
SiB:Al 8.68
Expan 6.69
Berry Rust (new)
================
SILICA.............. 25.13 23.14%
EPK KAOLIN.......... 22.69 20.90%
NEPHELINE SYENITE... 8.61 7.93%
FERRO FRIT 3134..... 19.93 18.35%
BONE ASH............ 8.97 8.26%
TALC................ 14.67 13.51%
RED IRON OXIDE...... 8.59 7.91%
========
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
Debby Grant on mon 28 jul 97
Hi Craig,
Can't thank you enough for all the work you have done on Berry Rust.
I, myself, have not been able to do any work for the past month. Finished
all my production for the shops and Sunapee Fair in early June and
then had to start concentrating on our summer business on a lake. I
was able to sit down at the wheel for the first time on Thursday and
then had to take off to the store on the lake again. I am anxious to try
your revised formula. Incidentally, I don't think the Berry Rust will look
as vibrant on porcellain as it does on an iron bearing clay. Also, my
kiln will have a quite different affect on the firing. I have a home made
electric kiln modeled on plans by Ed Scheier and modified by us. It
has 9 inch thick walls and cools very slowly. By the way, how did you
like the glaze? You never said.
Thanks again, Debby Grant in NH
Craig Martell on thu 31 jul 97
Hi Debby and the rest of you Rust lovers:
Yes I did forget to mention that I indeed liked the glaze. I think it's a
very rich oxidation glaze. I fired some tests in Red. to cone 10 and the
formula with the frit devitrified into a red crystalline satin matt which
was very nice. The original formula with gerstley borate still had a glassy
matrix with some suspended crystals which was also very nice. Which of the
two was the better glaze? Damned if I know! I guess it just depends on who
is looking at it. I wouldn't be hesitant about using either one.
I mixed up about a quart of each glaze and am going to let it set for a time
to see about the floculation problem. I was doing some reading on fluidity
in Hamers book (Potter's Dictionary) and came across some info about
particle size increasing and decreasing the fluidity of glazes. I
remembered that high iron glazes tend to need a bit more water to reach the
target Specific Gravity for good application. The iron being VERY fine
particle size, decreases the fluidity of the glaze by creating more surface
area. The combo of Gerstley Borate releasing Ca ions and the iron
decreasing the fluidity may be a double whammy that causes application
problems when the glaze has been in storage a while. Just a thought, if I'm
all wet here, will one of you please fax me a towel?
Debby, if you are interested in seeing my tiles, tell me where to send them
and I'll get a set of Ox and Red fired ones to you. Words can never
describe the way glazes look and feel.
Regards to all, Craig Martell-Oregon...always vigilant for offending ions!!
| |
|
