Holds and Oil Spot Glaze
satIron_ZG_1S_Z3J is a glaze in which bubbles form, rise to the surface and
pop. The result of these bubbles popping can
In
Firing Two of the two cone 10 firings, with no holds above 1750 degF,
there are no oil spots, yet crater remains of
In Firing One, with a four hour hold at 1750 deg F, and no
holds at any higher temperature, it is an oil spot glaze.
In the current firing, satIron_ZG_1S_Z3J is fired at cone 11.5, with a two
hour hold at 1800 deg F. It shows crater remains
It would seem that the higher hold distroys oil spots, yet its lack doesn't
guarantee them.
The blistering at the rim of the pot is the result of chemical interactions
after the glaze had matured, and is something
A hold at 1800 degF or above imparts an orange color.
The plate has a leaf print. Several closeups of the surface of the glaze,
including images of the interaction
A leaf is softened by soaking in water laced with trisodium phosphate. After
the pot is glazed, the leaf is pressed
plate is ~ 7 inches in diameter
The cone 11 is down past the bottom of the cone pat, both cone 12 and cone 13
are tipped.
150 deg F an hour to 250 deg F
400 deg F an hour to 1800 deg F
300 deg F an hour to 1965 deg F
120 deg F an hour to 2250 deg F
30 deg F an hour to 2325 deg F with a 20 minute hold at 2325 deg F
300 deg F an hour to 1800 deg F then a 2 hr hold at 1800 deg F
300 deg F an hour to 1700 deg F then a 3 hr hold at 1700 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.33
Al2O3 0.50
SiO2 3.4
molecular percent Silica 64.7%
K2O 0.43
Al2O3 0.54
SiO2 3.33
molecular percent Silica 48%
be an oil spot glaze, a
glaze with leopard spots, or a glaze exhibiting the result of the bubbles as
relics of the craters
resulting from the colapsed bubbles.
bubble action, and
leopard spots are visible. This is the coolest of the three firings being
discussed.
This is also a
cone/10 firing.
of bubble action, but no
oil spots.
I'd seen previously in high
alkaline glazes fired past maturation.
between the glaze and the wash over
the leaf embedded in the glaze are shown. A picture of the plate is also
shown.
into the glaze. When the glaze
dries, a swatch of plate including the leaf is coated with wax. When the wax
is dry, the leaf is removed and the indentations in the glaze are coated
with a very thin layer of an
underfired glaze.
Images of the surface and its interaction with the leaf wash
Image of the glaze satIron_ZG_1S_Z3J with leaf wash leaf_Z3K
oxidation firing to cone 11.5 in an electric kiln
Firing profile
Up Fire profile cone 11.5
Down Fire Profile cone 11.5
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Background Glaze:
Empirical Formula satIron_ZG_1S_Z3J:
Na2O 0.48
CaO 0.18
MgO 0.01
Fe2O3 0.17
P2O5 0.17
Empirical Formulae of leaf wash glaze leaf_Z3K:
Na2O 0.53
CaO 0.04
P2O5 0.15