Shifting Edges

The effect of decreasing iron in a high-phosphorus saturated-iron glaze.

With half the iron, a stiff, waxy, matte, saturated-iron glaze with dark, brooding leopard spots
morphs into a full gloss many-colored, low-viscosity glaze.

The mug with background glaze iron_satIron_Z2V_0PP has an inlay design glazed with iron_Alex_0.
The mug with background glaze iron_satIron_Z2V_0PP_MFe has an inlay design glazed with
alk_179_1_Z30_0Var.

The design 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, using a bulb syringe
with a needle applicator.

Image of the glaze iron_satIron_Z2V_0PP

full view

Image of the glaze iron_satIron_Z2V_0PP_MFe

full view

Mugs are ~4.5 inches high.

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

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 iron_satIron_Z2V_0PP :

K2O        0.11
Na2O       0.37
Li2O       0.29
CaO        0.18
MgO        0.05

Al2O3      0.56
Fe2O3      0.20

SiO2       3.2
P2O5       0.17
TiO2       0.02

molecular percent Silica 62%

Empirical Formula iron_satIron_Z2V_0PP_MFe :

K2O        0.11
Na2O       0.37
Li2O       0.28
CaO        0.19
MgO        0.05

Al2O3      0.56
Fe2O3      0.10

SiO2       3.2
P2O5       0.17
TiO2       0.02

molecular percent Silica 63%

Empirical Formula iron_Alex_0 :

K2O        0.08
Na2O       0.37
Li2O       0.14
CaO        0.31
MgO        0.10

Al2O3      0.57
Fe2O3      0.15

SiO2       2.98
P2O5       0.03

molecular percent Silica 63%

Empirical Formula alk_179_1_Z30_0Var :

K2O        0.17
Na2O       0.19
Li2O       0.25
CaO        0.02
MgO        0.27
BaO        0.10

Al2O3      0.53
Fe2O3      0.04

SiO2       2.43
TiO2       0.16

molecular percent Silica 58%

Remarks

As iron is a flux at cone 10, it's interesting that reducing the iron produced a more fluid glaze.

The pin-prick white spots in the photograh of the mug with iron_satIron_Z2V_0PP are pinholes,
which are gone in the more fluid glaze iron_satIron_Z2V_0PP_MFe.

Carol's Home Page