Magnesium vs. Calcium
Decreased Magnesium results in the appearance of metallic micro-crystals and a
more fluid melt.
The second glaze was generated from the first by replacing Dolomite with Bone
Ash, which increased the surface coverage by
The glaze with high MgO
A variegated opaque waxy matte glaze with black, red, and orange markings in a
tan matrix.
glaze with less MgO, and slightly higher P2O5.
Where thick, this glaze is covered with metallic micro-crystals in a glossy
orange-y brown matrix. An even thicker application gives dense
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 2300 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 .2
Al2O3 .5
SiO2 2.94
molecular percent Silica 61%
K2O .2
Al2O3 .51
SiO2 3
molecular percent Silica 61%
The effect on the appearance of the glaze of replacing MgO with CaO, and
slightly increasing P2O5, is substantial.
The higher MgO glaze satIron_ZG_1S_1Munge_3, has large pinholes where thickly
applied, and incompletely-healed bubbles on the rim.
To what is attributed the appearance of the metallic micro-crystals in
satIron_ZG_1S_1Munge_3MMg_0?
metallic
micro-crystals, while simultaneously eliminating a colorful range of
in-homogeneities.
Glaze satIron_ZG_1S_1Munge_3
bowl is ~4 inches in diameter
Glaze satIron_ZG_1S_1Munge_1Munge_3MMg_0
black leopard
spots. As a result of a thinner glaze application, the outside of the pot is
dark brown with a
scattering of micro-crystals.
bowl is ~4 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 glaze satIron_ZG_1S_1Munge_3 :
Na2O .42
Li2O .19
CaO .1
MgO .09
Fe2O3 .18
P2O5 .12
Empirical Formula Glaze satIron_ZG_1S_1Munge_3MMg_0
Na2O .43
Li2O .2
CaO .16
MgO .01
Fe2O3 .19
P2O5 .16
Remarks
These
defect can be attributed to high viscosity, and a glaze on the edge of
being underfired.
Replacing Dolomige with Bone Ash both
replaced MgO with CaO and increased P2O5, I attribute the greater part of the
change
to the increased CaO, which results in a more fluid and uniform
melt. The greater fluidity of the lower MgO melt,
satIron_ZG_1S_1Munge_3MMg_0, facilitates the growth of the golden metallic
micro-crystals.
By contrast, in the higher MgO melt, more immiscible
components are present, generating distinct colors and textures.