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 celedon_PA_Z2D, the foreground design is
glazed with hankPaper_Z1R_2C_1, and contains cobalt and copper.
The background glaze is blue in an oxidation firing as it contains silicon
carbide as a local reducing agent.
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 .17
Al2O3 .4
SiO2 3.82
molecular percent Silica 73%
0.02% Silicon Carbide added
K2O .13
Al2O3 .42
SiO2 2.7
molecular percent Silica 63%
Added:
1% cobalt carbonate
The background glaze and inlay glaze belong to different glaze families. The
background glaze is high in silica and calcia;
The copper, which in the inlay glaze is dominated by the cobalt, moves across
the inlay boundary to form a black frame
This strong red in the background of a relatively viscous glaze suggests the
possibility that the background glaze with copper added
The black fringe is copper diffusing
from the inlay into the background.
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_Z2D and inlay hankPaper_Z1R_2C_1
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
Empirical Formula celedon_PA_Z2D :
Na2O .18
CaO .5
MgO .06
ZnO .09
Fe2O3 .01
Inlay Glaze
hankPaper_Z1R_2C_1 :
Na2O .12
Li2O .05
CaO .14
MgO .02
BaO .3
SrO .24
TiO2 0.14
0.7% Copper Carbonate
Remarks
the inlay glaze is high in
baria and strontia. The high viscosity of both background and inlay glazes is
a consequence
of the firing. Both of these glazes are fired near the
bottom of their respective maturation temperature ranges.
surrounding the inlay in the
background region. Bits of copper red in the black cloud announce this as the
copper and not the cobalt.
might be a copper
red glaze in local reduction.