Jeff Lawrence on mon 15 may 00
Hello Clayart,
I've been working toward a reliable crackle glaze for my cone 04 slipcast
earthenware light fixtures and am stumbling. My goal is a regular crackle
pattern which I can ink in with black.
My issues are the following:
- different glaze thickness produces different crackle density and
patterns - is
this inevitable?
- bubbles remain, even when the glaze is so liquid it runs
off the pot!
- Inking is recommended only with hot ware; I can think of no
safe/efficient way to put this into production.
- there is considerable delayed crazing, so that some of the lines get inked
and some appear afterward, for an inconsistent effect.
- I append two recipes with anomalous results. 04CrklA crackled well, though
with the problems cited above -- very runny. 04crklD didn't crackle, even
though the calculated coe is higher (I added tin to make it opaque). Any
diagnoses? This may be an error
A point to ponder: Mimi Obstler, in "Earth and Fire," talks about different
crazing patterns with different materials and recommends using G-200
feldspar because it reliably produces "chrysanthemum pattern" crazing.
Sounded
good to me, but she offered no theories on how this material differs from
others that produce patterns less chrysanthemumey. Any hypotheses?
If you have any suggestions to elucidate, alleviate, mitigate or obliterate
these symptoms, I'd be grateful.
Jeff Lawrence vox: 505 753 5913
Sun Dagger Design fax: 505 753 8074
18496 US HWY 84/285 jml@sundagger.com
Espanola NM 87532 www.sundagger.com
04 Crackle base 04crcklA
========================
FRIT 3134........... 3.50 13.46%
EPK KAOLIN.......... 2.50 9.62%
NEPHELINE SYENITE... 7.00 26.92%
WOLLASTONITE........ 2.00 7.69%
FRIT 3269........... 7.00 26.92%
*Tin oxide........... 1.00 3.85%
Cadycal............. 3.00 11.54%
========
26.00
CaO 0.52* 10.48%
MgO 0.00* 0.04%
K2O 0.11* 3.84%
Na2O 0.36* 7.93%
ZnO 0.01* 0.29%
TiO2 0.00 0.04%
Al2O3 0.41 14.90%
B2O3 0.55 13.85%
P2O5 0.00 0.03%
SiO2 2.24 48.43%
Fe2O3 0.00 0.15%
MnO 0.00* 0.01%
Cost/kg 18.48
Si:Al 5.51
SiB:Al 6.88
Expan 9.01
04 Crackle base - 04CRKLd
=========================
EPK KAOLIN.......... 7.27 7.17%
FRIT 3134........... 14.55 14.35%
NEPHELINE SYENITE... 25.45 25.11%
WOLLASTONITE........ 7.27 7.17%
FRIT 3269........... 21.82 21.52%
*Tin oxide........... 5.00 4.93%
VEEGUM T............ 5.45 5.38%
WHITING............. 14.55 14.35%
========
101.36
CaO 0.65* 17.63%
MgO 0.00* 0.04%
K2O 0.08* 3.63%
Na2O 0.26* 7.98%
ZnO 0.01* 0.26%
TiO2 0.00 0.04%
Al2O3 0.28 14.08%
B2O3 0.24 8.03%
P2O5 0.00 0.02%
SiO2 1.65 48.14%
Fe2O3 0.00 0.14%
MnO 0.00* 0.01%
Cost/kg 18.86
Si:Al 5.80
SiB:Al 6.64
Expan 9.77
Notes:
02-22-00 trying for crackle finish on slip ware Result: runs badly, but
crackles very good. Since crackle pattern is small -- <1/4"island on
average, I'll add alumina and silica to increase
viscosity and increase island size. Also, clarity detracts from
effect --will add opacifier as well.
04CRKLB -- added alumina to counteract running; still runny; coe of 9.4
04CRKLC -- more alumina and zircopax for coe of 9.22; didn't crackle enough
04CRKLD: using tin oxide instead of zircopax for COE 9.77; satin where
thick -- no crackle??
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