Less Silica
A small decrease in silica produced a large difference in crystal growth in
two tenmoku glazes.
The Glaze iron_satIron_Z2W_Z2Z was derived from the glaze
iron_satIron_Z2W_Z2Y_0 by a decrease
Images are shown of the precursor glaze, iron_satIron_Z2W_Z2Y_0 with higher
silica, and its derived
This is the glaze with higher silica.
The derived glaze, the glaze with lower 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
K2O 0.11
Al2O3 0.66
SiO2 3.74
molecular percent Silica 66%
K2O 0.10
Al2O3 0.66
SiO2 3.4
molecular percent Silica 64%
Both glazes are comprised of a glossy black matrix with a dusting of coppery
colored micro-crystals. In the glaze with
Presumably, the iron is more soluble in the higher silica glaze, so during the
cooling less iron precipitates
in silica; there were slight shifts
in other oxides to accommodate this reduction in silica.
glaze iron_satIron_Z2W_Z2Z_0.
Image of the precursor glaze, iron_satIron_Z2W_Z2Y_0
inside
outside
bowl is is 3 inches in diameter
Image of the glaze iron_satIron_Z2W_Z2Z_0
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 iron_satIron_Z2W_Z2Y_0 :
Na2O 0.48
Li2O 0.28
CaO 0.02
MgO 0.11
Fe2O3 0.24
Empirical Formula iron_satIron_Z2W_Z2Z_0 :
Na2O 0.50
Li2O 0.26
CaO 0.03
MgO 0.11
Fe2O3 0.22
Remarks
the reduced silica, the density of
the micro-crystals is significantly greater.
to form the micro-crystals.