Shifting Edges

A glaze which shifts from matte to gloss with an increase in alumina and silica, is shown here .

In this note by contrast a change in the balance of alkali metals to alkaline earths, with constant
alumina and silica causes a similar shift in texture.

The glaze longquan-iron-shino-Z38-0 is an iridescent metallic semi-matte which is mixed black
and purple with hints of brown. The semi-matte surface is the result of microcrystals on its surface,
as is most easily seen in the image of its outside.

The glaze longquan-iron-shino-Z38-1 has an opaque glossy variegated brown surface with coppery
highlights, and a metallic sheen.

These two glazes have nearly identical alumina and silica, but longquan-iron-shino-Z38-1 has
higher alkaline earths and lower alkali metals. To muddy the waters, it also has lower Fe2O3.

Image of the glaze longquan-iron-shino-Z38-0

full view

inside

full view

outside

bowl is ~ 4 inches in diameter.

Image of the glaze longquan-iron-shino-Z38-1

full view

inside

full view

outside

bowl is ~ 4 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 longquan-iron-shino-Z38-0 :

K2O        0.14
Na2O       0.44
Li2O       0.20
CaO        0.17
MgO        0.05

Al2O3      0.97
Fe2O3      0.17

SiO2       3.6

molecular percent Silica 62.6%

Empirical Formula longquan-iron-shino-Z38-1 :

K2O        0.13
Na2O       0.41
Li2O       0.20
CaO        0.21
MgO        0.05

Al2O3      0.97
Fe2O3      0.14

SiO2       3.5

molecular percent Silica 62.4%

Remarks

The glaze longquan-iron-shino-Z38-0 does have slightly higher silica, which I consider negligible when compared
to the difference in alkali metal:alkaline earth ratios. The alkali metal:alkaline earth ratio of longquan-iron-shino-Z38-0
is 3.5, while that of longquan-iron-shino-Z38-1 is 2.85.

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