Increasing Silica
The effect of increasing Silica in an oil spot glaze.
here I showed a glaze which with more silica was transformed into an oil
spot glaze.
So I wondered what the effect of increasing silica would be on an oil spot
glaze.
The glaze longquan_iron_mashiko_0 is an oil spot glaze, black with silvery oil
spots. I increased the silica in
If the glaze is applied thickly, the resulting oil spots are larger and cover
more of the surface. If that glaze
bowl is ~ 4 inches in diameter.
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 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 50 min hold at 1750 deg F
50 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 0.71
SiO2 4.27
molecular percent Silica 69%
K2O 0.11
Al2O3 0.72
SiO2 4.72
molecular percent Silica 71%
The small differences in the non-silica components of the empirical formula
are an artifact of the method
that glaze to get the glaze
longquan_iron_mashiko_0_PSi.
is applied thin, the oil spots take
over, producing a silver metallic glaze, as is seen on the outside of the
bowl.
Image of the low silica glaze longquan_iron_mashiko_0
inside
outside
Image of the high silica glaze longquan_iron_mashiko_0_PSi
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 longquan_iron_mashiko_0 :
Na2O 0.45
Li2O 0.15
CaO 0.11
MgO 0.18
Fe2O3 0.19
Empirical Formula longquan_iron_mashiko_0_PSi :
Na2O 0.45
Li2O 0.16
CaO 0.11
MgO 0.17
Fe2O3 0.20
Remarks
used to increase silica. I added silica to
the glaze longquan_iron_mashiko_0, then normalized the recipe to add to 100.