Less Silica
A small decrease in silica produced different crystals in an altered matrix,
this in a high alkali metal glaze containing BaO.
The glaze alk_179_Z30_0 was derived from the glaze alk_179_1_Z2Z by a
decrease in silica;
Images are shown of the precursor glaze, alk_179_1_Z2Z 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 0.16
Al2O3 0.52
SiO2 3.17
molecular percent Silica 64%
K2O 0.16
Al2O3 0.52
SiO2 2.45
molecular percent Silica 59%
Both glazes are comprised of a glossy brown matrix with variegated
yellow-colored micro-crystal clusters. In the glaze with
The lower silica glaze has considerably lower viscosity that its higher
silica parent; it dripped
after normalization of the recipe to 100, there were slight
shifts in other oxides to accommodate this reduction in silica.
glaze alk_179_Z30_0.
Image of the precursor glaze, alk_179_1_Z2Z
inside
outside
bowl is is 3 inches in diameter
Image of the glaze alk_179_Z30_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 alk_179_1_Z2Z :
Na2O 0.19
Li2O 0.25
CaO 0.02
MgO 0.27
BaO 0.11
Fe2O3 0.05
TiO2 0.18
Empirical Formula alk_179_Z30_0 :
Na2O 0.19
Li2O 0.26
CaO 0.02
MgO 0.27
BaO 0.10
Fe2O3 0.04
TiO2 0.16
Remarks
the reduced silica,
the crystal clusters are significanlty larger, and the matrix has opalescent
markings.
onto the kiln shelf and allowed the crystal
clusters to grow larger.