leaves on oil spot glaze

Investigating distinct background glaze for leaf prints. Here an oil spot glaze gives a leaf dominated by
leopard spots. A fluid saturated iron glaze gives a fanciful sunset colored effect.

Both background glazes have nearly identical bases, with similar silica content as well. The primary
difference is that lis-Z3P has substantially higher alumina. This is visible in the substantially higher
viscosity of that glaze.

Oil spots are closely associated with bubbles forming in the glaze near the final part of the firing,
with the resulting artifacts of that event remaining. Perhaps for this reason a late maturing
saturated iron glaze is more likely to exhibit oil spots.

Image of the plate with glaze lis-Z3P and leaf wash leaf_Z3K.

full view

plate is ~ 7 inches in diameter.

Image of the plate with glaze satIron_ZG_Z3N_Z3Q and leaf wash leaf_Z3K.

full view

plate is ~ 7 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 1850 deg F then a 2 hour hold at 1850 deg F

300 deg F an hour to 1750 deg F then a 1 hour hold at 1750 deg F

300 deg F an hour to 1700 deg F then a 3 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 Clay Art Center in Tacoma, WA.

glaze compositions

Empirical Formula lis-Z3P :

K2O        0.17
Na2O       0.55
CaO        0.26
MgO        0.02

Al2O3      0.89
Fe2O3      0.22

SiO2       3.77
P2O5       0.07

molecular percent Silica 63.4%

Empirical Formula satIron_ZG_Z3N_Z3Q:

K2O        0.16
Na2O       0.55
CaO        0.27
MgO        0.02

Al2O3      0.66
Fe2O3      0.23

SiO2       3.65
P2O5       0.07

molecular percent Silica 65.1%

Empirical Formulae of leaf wash glaze leaf_Z3K:

K2O        0.43
Na2O       0.53
CaO        0.04

Al2O3      0.54

SiO2       3.33
P2O5       0.15

molecular percent Silica 48%

A leaf is softened by soaking in water laced with trisodium phosphate. After the pot is glazed, the leaf is pressed
into the glaze. When the glaze dries, a swatch of plate including the leaf is coated with wax. When the wax
is dry, the leaf is removed and the indentations in the glaze are coated with a very thin layer of an
underfired glaze.

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