Increase both Alumina and Silica

A warm colored, variegated matte iron glaze with mixed yellows, oranges and browns, migrates to cooler colors with
an increase in both alumina and silica. With more alumina and silica its colors shift to mixed blues, greens and browns.

Images are shown of the precursor glaze tsabar-celadon-iron-8 and its derived glaze
tsabar-celadon-iron-8-PAlSi, which has increased alumina and silica.

Image of the precursor glaze tsabar-celadon-iron-8

glaze tsabar-celadon-iron-8

full view

inside

full view

outside

bowl is ~3 inches in diameter

Image of the glaze tsabar-celadon-iron-8-PAlSi

The derived glaze, the glaze with additional alumina and silica.

full view

inside

full view

outside

bowl is is 3 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 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

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

glaze compositions

Empirical Formula tsabar-celadon-iron-8 :

K2O        0.18
Na2O        0.19
Li2O        0.10
CaO        0.47
MgO        0.02
ZnO        0.04

Al2O3        .57
Fe2O3        .11

SiO2        2.92

molecular percent Silica 63.3%

Empirical Formula tsabar-celadon-iron-8-PAlSi :

K2O        0.20
Na2O        0.20
Li2O        0.10
CaO        0.43
MgO        0.02
ZnO        0.05

Al2O3        0.63
Fe2O3        0.12

SiO2        3.21

molecular percent Silica 64.6%

Remarks

The glaze tsabar-celadon-iron-8-PAlSi, with increased alumina and silica, also has a slight shift of
alkaline earths to alkali metals.

The bowl glazed with tsabar-celadon-iron-8-PALSi has a thinner glaze coating than the bowl glazed with
tsabar-celadon-iron-8. This is most noticeable on its outside. The apparent transparency of the glaze
tsabar-iron-8-PalSi on the outside of the pot is the result of thinner glaze coverage.

I attribute the change in color primarily to the increased alumina and silica, as the shift from
alkaline earths to alkali metals is relatively small.

Iron colors are extremely sensitive to changes in the level of alumina.

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