more cobalt colors
These glazes, zincSr_Z3W_0, zincSr_Z3W_1, and zincSr_Z3W_2 are descendants of
zincSr_Z3S_0
shown here .
Prior descendants of zincSr_Z3S_0 are
shown here .
The appearance of these glazes is subtly transformed by an inversion of the
order of the downfire holds
in the firing. I show these glazes in the two
firings, Firing 1, and Firing 2.
Both Firing 1 and Firing 2 have the same upfire protocol.
Firing 1:
The downfire is my regular down firing, with holds at 1850 degF, 1750 degF, 1700 degF and 1650 degF.
Firing 2:
The downfire drops with a hold at 1650 degF, then rises back up with a hold at
1850 deg F, then back down
with a hold at 1700 deg F.
The reasoning behind inversion of the order of the downfire holds is discussed here .
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
with a needle applicator.
Image of the glaze zincSr_Z3W_0 in Firing 1
Image of the glaze zincSr_Z3W_0 in Firing 2
Image of the glaze zincSr_Z3W_1 in Firing 1
Image of the glaze zincSr_Z3W_1 in Firing 2
Image of the glaze zincSr_Z3W_2 in Firing 1
Image of the glaze zincSr_Z3W_2 in Firing 2
bowls are ~6 inches in diameter.
oxidation firing to cone 10 in an electric kiln
Firing profiles
Firing 1 profile
Up Fire profile cone 10
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 cone 10
300 deg F an hour to 1850 deg F then a 2 hr hold at 1850 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
300 deg F an hour to 1700 deg F then a 3 hr hold at 1700 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
Firing 2 profile
Up Fire profile cone 10
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 cone 10
300 deg F an hour to 1650 deg F then a 3 hr hold at 1650 deg F
300 deg F an hour to 1850 deg F then a 2 hr hold at 1850 deg F
300 deg F an hour to 1700 deg F then a 2 hr hold at 1700 deg F
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze composition
Empirical Formula zincSr_Z3W_0:
K2O 0.19
Na2O 0.28
CaO 0.02
MgO 0.19
SrO 0.14
ZnO 0.18
Al2O3 0.53
SiO2 3.08
molecular percent Silica 66.8%
Added:
2.5% Cobalt Carbonate
Empirical Formula zincSr_Z3W_1:
K2O 0.14
Na2O 0.35
CaO 0.02
MgO 0.24
SrO 0.15
ZnO 0.10
Al2O3 0.54
SiO2 2.8
molecular percent Silica 64.5%
Added:
2.5% Cobalt Carbonate
Empirical Formula zincSr_Z3W_2:
K2O 0.13
Na2O 0.34
CaO 0.02
MgO 0.17
SrO 0.17
ZnO 0.17
Al2O3 0.52
SiO2 2.78
molecular percent Silica 64.6%
Added:
2.5% Cobalt Carbonate
Inlay Glaze:
Empirical Formula inlay hiAlk_Z3P_Z3V_0:
K2O 0.18
Na2O 0.41
CaO 0.31
MgO 0.10
Al2O3 0.64
SiO2 3.54
P2O5 0.07
TiO2 0.21
molecular percent Silica 64.9%
Remarks
The glaze zincSr_Z3W_0 has the highest silica:alumina ratio of these three
glazes. It is seem to be more
fluid than the other two glazes, this is
visible in the appearance of a bit of gloss at the upper rim. The mixed pink
and blue color is striking.
Both zincSr_Z3W_1, and zincSr_Z3W_2 have a matte turquoise rim, whose inner edge is peach colored.
zincSr_Z3W_2 was applied overly thickly on the bowl in Firing 1, which
contributes to the extreme
overgrowth of micro-crystals. At the rim,
below the peach colored edge, is seen some violet markings mixed
in with the
pale lavender color which dominates the interior of the bowl in Firing 1.