Higher Calcium
A small increase in calcium produced a profusion of crystals,
this in a high alkali metal glaze.
The glaze satIron_Alex_Z30 was derived from the glaze satIron_P_Alex by a
shift toward the right in a line blend
Images are shown of the precursor glaze, satIron_P_Alex with lower
CaO, and its derived
This is the glaze with lower CaO.
The derived glaze, the glaze with higher CaO.
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 1750 deg F then a half hour hold at 1750 deg F
300 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
Precursor glaze with lower CaO.
K2O 0.08
Al2O3 0.65
SiO2 3
molecular percent Silica 63%
Derived glaze with higher CaO.
K2O 0.08
Al2O3 0.64
SiO2 3
molecular percent Silica 63%
K2O .07
Al2O3 .71
SiO2 3.13
molecular percent Silica 63%
K2O .09
Al2O3 .43
SiO2 2.7
molecular percent Silica 65%
The glaze satIron_P_Alex has some crystals in a glossy matrix, less than 50%
surface coverage; in contrast
The glaze satIron_Alex_Z30 has higher CaO and as a result an alkali metal:
alkaline earth ratio of 1.3:1;
satIron_Alex_Z30 with lower alkali metals, is less fluid, didn't drip, and no
shelf cleaning required.
In this case, more crystals grow in the higher viscosity, less
fluid glaze with lower alkali metals.
The crystals are acicular, as they
were in the precursor glaze, yet they have changed, being now matte.
of the two glazes satIron_ZG_Ip7_5
and alexanderBowl_0_Z1Y. The result was a glaze slightly higher in CaO,
and correspondingly lower in alkali metals.
glaze satIron_Alex_Z30.
Image of the precursor glaze, satIron_P_Alex
inside
outside
bowl is is 3 inches in diameter
Image of the glaze satIron_Alex_Z30
inside
outside
bowl is is 3 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula satIron_P_Alex :
Na2O 0.36
Li2O 0.16
CaO 0.23
MgO 0.17
Fe2O3 0.09
P2O5 0.03
Empirical Formula satIron_Alex_Z30 :
Na2O 0.33
Li2O 0.16
CaO 0.26
MgO 0.17
Fe2O3 0.07
P2O5 0.02
Empirical Formula satIron_ZG_Ip7_5 Left end of line blend:
Na2O .44
Li2O .2
CaO .12
MgO .17
Fe2O3 .1
P2O5 0.04
Empirical Formula alexanderBowl_0_Z1Y Right end of line blend :
Na2O .05
CaO .70
MgO .16
Remarks
the glaze satIron_Alex_Z30 has nearly dense
surface crystals, with only a bit of matrix peeking through.
lower than that of satIron_P_Alex, which is
1.5:1.