Increasing Silica

The effect of increasing Silica in a full gloss glaze with small crystals.

Both glazes have a transparent glossy pale amber background. The first piece has pale copper colored
acicular crystals. In the second piece, the crystals are smaller and more densely packed.
These are redish brown to brown, without either the coppery metallic glitter or the needles extending
radially from center to edge that figure so prominently in the first glaze.

The first glaze is satIron_Alex_Puah, the second, satIron_Alex_Z30_Puah_16_PMg. The name of the second glaze
is the consequence of the meandering nature of the development of the glaze itself. Through a migration
of many steps, a glaze developed which differs from its origin, the first glaze, by an increase in silica.

It is true that the second glaze is slightly higher in Fe2O3 and shifts a small amount of CaO to MgO. However
I consider those changes minor compared to the large increase in silica.

The design, which is not addressed in this analysis, is created by adhering a mask and then applying
the main glaze. After drying, the mask is removed and the open area filled in with a second glaze.

Image of the pieces

full view

vase with glaze satIron_Alex_Puah and inlay satIron_ZG_Ip7_5

vase is ~ 11 inches high.

full view

plate with glaze satIron_Alex_Z30_Puah_16_PMg and inlay hankPaper_Z1R_2C_1

Plate is ~10 inches in diameter

oxidation firing to cone 10 in an electric kiln

Firing profiles

Up Fire profile

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

Down Fire Profile

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

Clay body is a grolleg porcelain from Tacoma Clay Art Center.

glaze compositions

Empirical Formula satIron_Alex_Puah :

K2O        0.08
Na2O       0.33
Li2O       0.18
CaO        0.23
MgO        0.18

Al2O3      0.65
Fe2O3      0.07

SiO2       3.05
P2O5       0.03

molecular percent Silica 63.5%

Empirical Formula satIron_Alex_Z30_Puah_16_PMg :

K2O        0.08
Na2O       0.33
Li2O       0.17
CaO        0.22
MgO        0.20

Al2O3      0.65
Fe2O3      0.08

SiO2       3.74
P2O5       0.03

molecular percent Silica 67.9%

Carol's Home Page