Migrating abutting glazes
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 celedon_PA_Z2G_0PLi, the foreground design is
glazed with paperWhite_ZV_3_Z2H. paperWhite_ZV_3_Z2H contains cobalt.
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 0.1
Al2O3 0.41
SiO2 3.67
molecular percent Silica 72%
Added:
0.2% silicon carbide as a local reducing agent.
K2O 0.05
Al2O3 0.6
SiO2 3.2
molecular percent Silica 64.6%
Added:
1% cobalt carbonate
The nearly black shadow framing much of the inlay marks the original position
of the design.
The cobalt diffused into the background and then the inlay slid down the wall
of the bowl, leaving behind the cobalt
The edge of the interaction region bereft of its cobalt is, as a result,
white.
A reaction between inlay and background matrix is shown by the irregular
boundary between the inlay and matrix.
Likely both the CaO and ZnO diffused from high concentration in the matrix
to low concentration in the inlay to erode
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 celedon_PA_Z2G_0PLI and inlay glaze paperWhite_ZV_3_Z2H
bowl is ~6.5 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
celedon_PA_Z2G_0PLi :
Na2O 0.11
Li2O 0.08
CaO 0.43
MgO 0.2
ZnO 0.08
Inlay glaze
Empirical Formula paperWhite_ZV_3_Z2H :
Na2O 0.15
Li2O 0.20
CaO 0.02
MgO 0.02
BaO 0.28
SrO 0.28
TiO2 0.16
Remarks
Although it appears to be black, it is, upon close
inspection, deep cobalt blue.
which had diffused into the
background glaze. This diffusion started before the background glaze was
sufficiently melted
for the inlay to have slid down.
The inlay has been partially
absorbed into the background matrix to form something distinct from
either.
The background glaze has substantial CaO, of which the inlay has
only a trace.
There additionally is ZnO in the background glaze.
the edge of the inlay.