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 nepheline_Z1A_2MAlk, 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,
Previously I'd shown the glaze satIron_ZG_1O_1Q_1MFe as foreground glaze with
background glaze:
and with background glaze:
and also with background glaze:
Here, with the background glaze nepheline_Z1A_2MAlk, in contrast to the prior
examples, the interaction region separates
A thin black line resides within the masked region, having migrated inward from
the original boundary of the design region.
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 .08
Al2O3 .73
SiO2 4
molecular percent Silica 67%
K2O .24
Al2O3 .47
SiO2 3.17
molecular percent Silica 66%
After firing, the area covered by the design mask is reduced somewhat, but its
general shape is unchanged.
The inlay glaze is more fluid than the background glaze.
The fluid inlay glaze eats beneath the matrix glaze, and reacts with it to
form the frothy yellow and red inclusions.
These are both high alkali metal glazes with similar silica. The background
glaze nepheline_Z1A_2MAlk has
then the mask is removed
and the open area filled in with a second glaze.
along a boundary within the
original masked region into two distinctive bands.
On the background side of
this line is a defuse froth of mixed red and yellow foam
with a scattering
of silvery metallic crystals.
Close up Images of the interaction region
Image of the piece
bowl with glaze nepheline_Z1A_2MAlk 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 nepheline_Z1A_2MAlk :
Na2O .52
Li2O .06
CaO .11
MgO .23
Fe2O3 .22
Inlay Glaze
satIron_ZG_1O_1Q_1MFe :
Na2O .22
Li2O .24
CaO .16
MgO .14
Fe2O3 .09
P2O5 .04
Remarks
lower calcia, higher iron, magnesia,
alumina and no phosphorus. It is more fluid
than I would have expected
for its high alumina and relatively lower alkali metals.