Shifting Edges
The effect of changing the balance between the alkali metals potassium and
sodium in a saturated iron glaze is shown.
Both glazes, iron_Alex_00PSi_MMg_PK and iron_Alex_00PSi_MMg have total K2O +
Na20 equal 0.54. The first glaze has
The difference in appearance is substantial, the first has pale tan spots on a
nearly black background, the second a more
The design in the glaze iron_Alex_0PPSi_Pk is created by adhering a mask and
then applying the main glaze. After drying,
The inlay design is
glazed with longquan-iron-shino-Z39-0
bowl is ~6 inches in diameter.
bowl is ~ 4 inches in diameter.
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
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
K2O 0.33
Al2O3 0.58
SiO2 4
molecular percent Silica 69%
K2O 0.09
Al2O3 0.58
SiO2 4
molecular percent Silica 69%
K2O 0.14
Al2O3 0.98
SiO2 3.66
molecular percent Silica 62.9%
Note that the high potassium glaze has higher viscosity, it is less fluid than
the high sodium glaze. One sees the
higher K2O, the second higher Na2O.
The differences in the other oxides in their respective empirical
formulas
are negligible.
nuanced appearance. It has
several layers, showing multiple colors and a variety of crystals.
Additionally, it has
patches of iron red.
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 high potassium glaze iron_Alex_0PPSi_PK
inside
outside
Image of the high sodium glaze iron_Alex_0PPSi_MMg
inside
outside
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula iron_Alex_0PPSi_MMg_PK:
Na2O 0.21
Li2O 0.17
CaO 0.27
MgO 0.02
Fe2O3 0.16
P2O5 0.07
Empirical Formula iron_Alex_0PPSi_MMg:
Na2O 0.45
Li2O 0.17
CaO 0.27
MgO 0.02
Fe2O3 0.16
P2O5 0.07
Empirical Formula longquan-iron-shino-Z39-0:
Na2O 0.44
Li2O 0.20
CaO 0.14
MgO 0.08
Fe2O3 0.17
Remarks
higher fluidity in the puddle of
glaze in the bottom of the bowl glazed with iron_Alex_0PPSi_MMg, and in the
transparent rim
where the glaze has run down the sides of the bowl. This
is in contrast to the bowl glazed with iron_Alex_0PPSi_MMg_PK
where the
glaze on the rim shows some of the dark brown matrix colors, and the
colors are uniform on the side walls.