Increasing Silica
Two glazes which differ in the Silica:Alumina ratio.
The glaze satIron_ZG_1S_Z3J differs from the glaze
satIron_ZG_1S_1Munge_3MMg_MLi primarily in increased silica.
Both glazes have a dark matrix and micro-crystalline metallic particles, but
as a result of increased silica,
The first glaze, satIron_ZG_1S_1Munge_3MMg_MLi has an additional diffuse
random orangey-brown matte
The second glaze, satIron_ZG_1S_Z3J, with higher silica, is a stiffer
glaze. It has only the dark
bowl is ~ 4 inches in diameter.
150 deg F an hour to 250 deg F
400 deg F an hour to 1800 deg F
300 deg F an hour to 2170 deg F with a hold of 1 hour at 2170 deg F
120 deg F an hour to 2250 deg F
60 deg F an hour to 2270 deg F with a hold of 30 minutes at 2270 deg F
60 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 4 hour hold at 1750 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.25
Al2O3 0.49
SiO2 3.11
molecular percent Silica 63%
K2O 0.33
Al2O3 0.50
SiO2 3.4
molecular percent Silica 64.7%
The
sodium:potassium ratio has changed slightly as well, but that is unlikely to
have effected the result.
Both of these glazes are high in phosphorus.
the glaze satIron_ZG_1S_Z3J has a different
phase structure than that of its precursor, satIron_ZG_1S_1Munge_3MMg_MLi.
second phase that is edged in copper-colored
metallic micro-crystals, superimposed on a chocolate brown matrix.
Where
this glaze is thick, the dark matrix dominates. This glaze has so
substantially flowed into the middle of the tile,
that it left part of
the edge of the tile nearly bereft of glaze, an indication of its greater
fluidity.
ground with the metallic oil spots.
Image of the glaze satIron_ZG_1S_1Munge_3MMg_MLi
Test Tile ~2.5 inches on an edge
Image of the glaze satIron_ZG_1S_Z3J
inside
outside
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_ZG_1S_1Munge_3MMg_MLi :
Na2O 0.57
CaO 0.16
MgO 0.02
Fe2O3 0.17
P2O5 0.16
Empirical Formula satIron_ZG_1S_Z3J:
Na2O 0.48
CaO 0.18
MgO 0.01
Fe2O3 0.17
P2O5 0.17