Shifting Edges
The effect of replacing some ZnO with BaO in a nickel blue glaze with calico
markings.
A slightly underfired nickel blue glaze with calico markings morphs into a
waxy translucent golden brown
The glaze cooper_404_1Na_MAlk is a matte glaze with strong phase separation in
the form of sharply defined
bowl is ~ 4 inches in diameter. Clay body is Tacoma clay art center version
of B-Mix.
bowl is ~ 4 inches in diameter. Clay body is Tacoma Clay Art Center grolleg
Porcelain.
150 deg F an hour to 250 deg F
400 deg F an hour to 1800 deg F
300 deg F an hour to 2050 deg F
120 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 deg F
300 deg F an hour to 1850 deg F then a two hour hold at 1850 deg F
50 deg F an hour to 1700 deg F then a three hour hold at 1700 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.05
Al2O3 0.34
SiO2 2.3
molecular percent Silica 63.4%
Added:
1.5% Nickle oxide
K2O 0.05
Al2O3 0.34
SiO2 2.3
molecular percent Silica 63%
Added:
1.5% Nickle oxide
The pitting
As noted above, these two glazes differ primarily in the ratio of ZnO:BaO.
glaze when some ZnO is replaced by BaO.
polygonal regions of contrasting color, which
I've described as calico markings. Its near neighbor glaze,
cooper_404_1Na_MAlk_0, with the same alumina, silica and alkali metals, has
two vertical layers.
The bottom layer is opaque with faint calico
markings; the over layer is translucent and golden brown.
The bowl glazed with cooper_404_1Na_MAlk_0 has a considerably thicker layer of
glaze on its inside than
on its outside. This accounts for the dominance of
the brown layer on its inside.
Image of the glaze cooper_404_1Na_MAlk
inside
outside
Image of the glaze cooper_404_1Na_MAlk_0
inside
outside
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
glaze compositions
Empirical Formula cooper_404_1Na_MAlk :
Na2O 0.25
CaO 0.01
MgO 0.02
BaO 0.26
ZnO 0.41
Empirical Formula cooper_404_1Na_MAlk_0 :
Na2O 0.25
CaO 0.01
MgO 0.02
BaO 0.34
ZnO 0.33
Remarks
which so disfigures cooper_404_1Na_MAlk is resolved by the
replacement of some ZnO with BaO;
though this change destroyed the calico
marking and the glittery needle zinc crystals of
cooper_404_1Na_MAlk.