Migrating disparate abutting glazes
The interface of adjacent glazes from divergent glaze families. The matrix
glaze and inlay glaze overlap by no more
than an eighth of an inch before
firing, with no overlap whatever for large parts of the design. The original
mask for the inlay had a smooth outline, but developed a jagged
appearance along the non-vertical edges
of the interfacial region. The
position of the original mask is approximated by running a
rubber band
about the top edge of the interaction region.
The matrix glaze is a high iron glaze, high in alkali metals and
alumina, the inlay glaze by contrast
is high in alkaline earths, lower in
alumina and contains titanium.
Several closeups of the interaction region of the two glazes are shown and, for context, a picture of the pot.
The background glaze is mashiko_alk_179_Z30-0; the foreground design is glazed with hankPaper_Z1R_2C_1.
A different saturated iron glaze with a foreground design in hankPaper_Z1R_2C_1
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.
Close up Images of the interaction region
Image of the piece
bowl with glaze mashiko_alk_179_Z30-0 and inlay hankPaper_Z1R_2C_1
bowl is ~7.5 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 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
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Background glaze
Empirical Formula mashiko_alk_179_Z30-0 :
K2O 0.15
Na2O 0.35
Li2O 0.22
CaO 0.10
MgO 0.18
Al2O3 0.69
Fe2O3 0.20
SiO2 3.84
molecular percent Silica 67%
Inlay Glaze
Empirical Formula hankPaper_Z1R_2C_1 :
K2O 0.12
Na2O 0.12
Li2O 0.05
CaO 0.14
MgO 0.02
BaO 0.31
SrO 0.24
Al2O3 0.42
SiO2 2.7
TiO2 0.14
molecular percent Silica 63%
Added:
1% Cobalt Carbonate .67% Copper Carbonate
Remarks
The background glaze is an oil spot glaze with medium viscosity that is higher
in alkali metals, silica and alumina.
By contrast, the inlay glaze is
exceedingly fluid and high in BaO and SrO.
The mask for the inlay is a simple zigzag pattern. After firing a large part
of the area between
the zig's and zag's is a mixture of inlay glaze and
matrix glaze.
Separating the inlay glaze from the matrix is a depletion region which is
pale ivory, showing that
the various oxides in the two glazes diffuse at
different rates.
Needle crystals are seen in the interface between the depletion region and the matrix (background) glaze.
Note the ripples in the edge of the interface. The matrix glaze, an oil spot
glaze, has multiple phases
with distinct compositions and viscosities. The
result of this non-uniformity is incoherent mixing and
interaction of the
matrix glaze and inlay glaze.