John Boyd on sun 22 jul 01
Dear Potters,
Perhaps I am reading too fast or not enough. I'm going over
Mr.Rhodes' book on Clay and Glaze, as well as Mr. Chappell's book on the
same subjects. I would really like to know what is causing the blue crystal
formation in this glaze (see below, feel free to use -purely decorative/not
food safe I think). Is it the interaction of the titanium/copper whithin a
very glassy matrix, or does the iron come into play as well?
Can I leave the iron out?
Thank you,
John
P.S. I fired this glaze the sam a s the shino. Both were a slow cool for 20
hours before unloading.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++ copper green Caswell Faux Oribe (Straw Glaze variation) +++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Range: 5-6
Firing type: Ox. or Red.
Glaze type: Mid-fire
Color: deep emerald green w/blue crystals in runs and iron spots
Surface: Gloss
Transparency: Translucent
Visual texture: Speckled/Flowing
Crystals: Small
Flow: Extreme
Flaws: Crazes
Testing: Tested
Date: 07/22/2001
Dolomite 13.09 13.1%
Lithium carbonate 3.30 3.3% Health warning!
Whiting 4.00 4.0%
Frit 3134 27.47 27.5%
EPK 22.18 22.2% Health warning!
Flint 29.97 30.0% Health warning!
-------- ------
100.00 100.0%
Copper carbonate 6.19 6.2% Health warning!
Copper oxide 6.29 6.3% Health warning!
Tin oxide 3.00 3.0%
Red iron oxide 0.50 0.5%
Bentonite 2.00 2.0% Health warning!
Variations:
Try spraying an even coat of glaze rather than dipping to get more of the
crystals.
Try spraying thick at the top, even on the bottom like an ash glaze for
blue runs.
Notes:
This glaze is a variaton of the Straw Glaze in Richard Malmgren's Ceramics
Monthly article "My Way With Clay."
I have simply saturated the copper content. However, it is the glossiest,
true emerald greens I have seen in my tests for ^6 Oxidation.
This glaze enjoys thickness/running to develop the blue crystal growths
and flows.
Material Hazards:
Lithium carbonate - toxic
EPK - dust hazard
Silica - dust hazard
Copper carbonate - toxic
Copper oxide - toxic
Bentonite - dust hazard
Cost: $ 3.61 per kg glaze
$ 0.36 per 100.001 g batch
===========================
Chemical Analysis
===========================
Na2O 0.09 Al2O3 0.17 SiO2 1.78
K2O 0.00 B2O3 0.18 P2O5 0.00
MgO 0.14 TiO2 0.00
CaO 0.42 Fe2O3 0.01
Li2O 0.09 SnO2 0.04
CuO 0.26
Alumina:Silica ratio is 1.00 : 10.63
Neutral:Acid ratio is 1.00 : 5.27
Alkali:Neutral:Acid ratio is 1.00 : 0.35 : 1.83
Weight percentages:
Na2O 2.8% Al2O3 8.4% SiO2 52.8%
K2O 0.1% B2O3 6.2% P2O5 0.1%
MgO 2.9% TiO2 0.1%
CaO 11.6% Fe2O3 0.7%
Li2O 1.3% SnO2 2.9%
CuO 10.0%
Volatiles:
CO2 11.9%
Other 3.4%
Loss On Ignition: 13.3%
Molecular percentages:
Na2O 2.9% Al2O3 5.3% SiO2 56.0%
K2O 0.1% B2O3 5.7% P2O5 0.0%
MgO 4.5% TiO2 0.1%
CaO 13.2% Fe2O3 0.3%
Li2O 2.8% SnO2 1.2%
CuO 8.0%
Expansion coefficient: 66.3 x 10e-7 per degree C
Oxides causing abnormal expansion effects: Li2O B2O3
Viscosity index: 45.7
Surface tension index: 362.9 (c/5) 362.0 (c/6)
(estimate based on oxides composing 87% of fired weight)
Onset of oxide volatization:
CO,CO2 700 C (c/018) (complete loss)
CuO 1000 C (c/06) (partial loss)
Na2O 1100 C (c/02) (partial loss)
B2O3 1150 C (c/2) (partial loss)
K2O 1200 C (c/6) (slight loss)
Materials in glaze:
Dolomite supplies CaO and MgO.
Lithium carbonate supplies Li2O.
Whiting supplies CaO.
Frit 3134 supplies SiO2, B2O3, CaO, and Na2O.
EPK supplies SiO2, Al2O3, Fe2O3, TiO2, and small amounts of
several fluxes.
Silica supplies SiO2.
Copper carbonate supplies CuO.
Copper oxide supplies CuO.
Tin oxide supplies SnO2.
Red iron oxide supplies Fe2O3.
Bentonite supplies SiO2, Al2O3, Fe2O3, TiO2, and small amounts
of several fluxes; bentonite helps to suspend glazes.
Oxides in glaze:
Na2O is a strong alkaline flux.
K2O is a strong alkaline flux.
MgO is a high-temperature flux.
CaO is a high-temperature flux.
Li2O is a strong alkaline flux.
CuO is a colorant (greens, blue-greens, reds, and copper lusters).
Al2O3 increases viscosity, prevents crystallization, and adds durability.
B2O3 is both a glass-former and a flux over a wide temperature range.
SiO2 is the primary glass-former in glazes.
P2O5 is a glass-forming oxide and opacifier.
TiO2 adds opacity and encourages crystal formation.
Fe2O3 is a colorant (tan, yellow, brown, red, and black).
In reduction, Fe2O3 -> FeO, which is a flux and colorant (brown, black).
SnO2 is an opacifier and whitener.
Comparison to limit formula "c/04 Matt"
0.0 0.5 1.0
KNaO : |-*----;----;--| : : : : : : : 0.09
CaO : |-;----;----;----;*-| : : : : : : 0.42
MgO |----;-*--;----;--| : : : : : : : 0.14
Li2O |---*;--| : : : : : : : : : 0.09
ZnO *----;----;----;--| : : : : : : : 0.00
BaO *----;----;----;----;----| : : : : : 0.00
SrO *----;----;----;----;----| : : : : : 0.00
PbO *----;----;----;----| : : : : : : 0.00
0.0 1.0 2.0
Al2O3 : |*;--| : : : : : : : : : 0.17
B2O3 |----*----;--| : : : : : : : : 0.18
0.0 5.0 10.0
SiO2 : |---*;----| : : : : : : : 1.78
=======================
Cost Summary
=======================
Dolomite 13.1% $ 0.06 per kg glaze
Lithium carbonate 3.3% $ 0.36
Whiting 4.0% $ 0.02
Frit 3134 27.5% $ 1.15
EPK 22.2% $ 0.11
Flint 30.0% $ 0.13
------ -------
100.0% $ 1.83 per kg glaze
Copper carbonate 6.2% $ 0.54 per kg glaze
Copper oxide 6.3% $ 0.52
Tin oxide 3.0% $ 0.68
Red iron oxide 0.5% $ 0.01
Bentonite 2.0% $ 0.02
-------
$ 1.77 per kg glaze
Total cost: $ 3.61 per kg glaze
$ 0.36 per 100.001 g batch
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Wade Blocker on mon 23 jul 01
John,
Your recipe is a saturated copper glaze, hence the crystal formation. Mia
in ABQ
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