Higher Silica
An increase in silica changed the form of the micro-crystals, and in addition,
created an additional yellow and
In addition to the occurance of the yellow and red precipitate, the matrix now
has tortoise shell colors.
Images are shown of the precursor glaze, satIron_P_Alex with lower
silica, and its derived
This is the glaze with lower silica.
The derived glaze, the glaze with higher silica.
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 silica.
K2O 0.06
Al2O3 0.66
SiO2 3.44
molecular percent Silica 66%
The glaze satIron_P_Alex has some crystals in a glossy matrix; as expected, the
glaze satIron_P_Alex_PSi has fewer crystals.
satIron_P_Alex_PSi with higher silica, is less fluid, didn't drip, and
while it has fewer of the acicular crystals
SatIron_P_Alex_PSi inadvertently also has higher P2O5, might that be the cause
of the change in color
red precipitate. This in a high alkali
metal glaze. The crystals are acicular, as they were in the precursor
glaze,
yet they have changed, being now translucent.
It remains crazed, though not as disfiguringly so
as in the precursor glaze.
glaze satIron_P_Alex_PSi.
Image of the precursor glaze, satIron_P_Alex
inside
outside
bowl is is 3 inches in diameter
Image of the glaze satIron_P_Alex_PSi
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_P_Alex_PSi :
Na2O 0.34
Li2O 0.21
CaO 0.23
MgO 0.16
Fe2O3 0.1
P2O5 0.06
Remarks
The appearance of the red
and yellow precipitate and the change in the color of the matrix is
unexpected,
as is the translucence and the color change of the
crystals. The nature of the glaze has changed.
is otherwise a more interesting
glaze.
and additional precipitate?