Changing the Silica:Alumina Ratio
Two glazes which differ primarily in the silica:alumina ratio.
The difference in silica:alumina ratio is large compared to the difference in
either of the component oxides.
satIron_ZG_0_PK_MLi is shown in two firings, which differ only in the
down-fire. The first firing for
satIron_ZG_0_PK_Z3L is shown only in the second firing. The inside also has
black micro-crystals, but the
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 1800 deg F then a 2 hr hold at 1800 deg F
300 deg F an hour to 1750 deg F then a 1 hr 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
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 4 hour hold at 1750 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.12
Al2O3 0.64
SiO2 3.23
molecular percent Silica 62.2%
K2O 0.14
Al2O3 0.67
SiO2 3.16
molecular percent Silica 61.5%
The balance of alkali metals to alkaline
earths is the same. The first glaze, satIron_ZG_0_PK_MLi, has higher
silica:alumina ratio, with higher silica and lower alumina. The balance
of sodium to potassium
is also slightly lower.
satIron_ZG_0_PK_MLi has an addition hold
at 1800 deg F, and has a shorter hold at 1750 deg F. In this firing,
while this glaze shows substantial coloration not visible in the second
firing, the black precipitates
are present over much of the surface.
This first variant firing of this glaze is shown to emphasize that these
black micro-crystals are characteristic of this glaze.
It has prominent black inclusions visible on the walls
in addition to
on the bottom in the first firing, and visible as dendritic precipitates in
the second firing.
exterior is covered in coppery colored metallic
micro-crystals which is not seen in either firing of the glaze
satIron_ZG_0_PK_MLi.
Image of the glaze satIron_ZG_0_PK_MLi in firing 1
inside
outside
Inage of satIron_ZG_0_PK_MLi and satIron_ZG_PK_Z3L in Firing 2
Image of the glaze satIron_ZG_0_PK_MLi
closeup of a section of a plate
Image of the glaze satIron_ZG_0_PK_Z3L
inside
outside
oxidation firing to cone 10 in an electric kiln
First Firing
Up Fire profile Firing 1
Down Fire Profile Firing 1
Second Firing
Up Fire profile Firing 2
Down Fire Profile Firing 2
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula satIron_ZG_0_PK_MLi :
Na2O 0.69
CaO 0.18
MgO 0.01
Fe2O3 0.22
P2O5 0.10
Empirical Formula satIron_ZG_0_PK_Z3L :
Na2O 0.66
CaO 0.18
MgO 0.02
Fe2O3 0.21
P2O5 0.10