Reactions at the interface between two glazes
The interaction at the interface of adjacent glazes.
Several closeups of the interaction region of the two glazes are shown and,
for context, a picture of the pot.
The background glaze is satIron_ZG_4, the foreground design is
glazed with satIron_ZG_1O_1Q_1MFe
The design is created by adhering a mask and then applying the main
glaze. After drying, the entire pot is coated in wax,
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 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
K2O .10
Al2O3 .56
SiO2 3.54
molecular percent Silica 66%
K2O .24
Al2O3 .47
SiO2 3.17
molecular percent Silica 66%
After firing, the area covered by the design mask is reduced to half its
original width.
The fluid inlay glaze eats beneath the matrix glaze allowing crystals formed
in the matrix glaze to migrate into the design region.
Chemical reactions and fluid flow combine unpredictably.
Here, the difference in behavior between these two glazes is especially
striking because the inlay glaze satIron_ZG_1O_1Q_1MFe is derived,
These are both high alkali metal glazes with similar silica, and
silica:alumina ratio.
then the mask is removed
and the open area filled in with a second glaze.
Close up Images of the interaction region
Image of the piece
bowl with glaze satIron_ZG_4 and inlay satIron_ZG_1O_1Q_1MFe
bowl is ~9 inches in diameter
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
Background glaze
Empirical Formula satIron_ZG_4 :
Na2O .50
Li2O .18
CaO .16
MgO .06
Fe2O3 .2
P2O5 .04
Inlay Glaze
satIron_ZG_1O_1Q_1MFe :
Na2O .22
Li2O .24
CaO .16
MgO .14
Fe2O3 .09
P2O5 .04
Remarks
An opaque version of
the inlay glaze peeks out between discrete matrix crystals.
by a
convoluted path, from the same root glaze as satIron_ZG_4.
satIron_ZG_4 has somewhat higher alumina and silica,
and lower Magnesia. I'd not have predicted the difference
in either
viscosity, nor crystal growth. I'd especially not have predicted that higher
viscosity
would combine with greater crystal growth.