reversing the order of down-fire holds
The glaze zincSr_Z3W_0 is
shown here in several distinct firings.
Those firings had several down-fire holds. To simplify the firing and
provide further evidence
These firings have holds only at the temperatures 1650 degF and 1900 degF.
The glazes in this firing has an underglaze decoration created by
slip trailing a
I show another glaze ironYellow in these same two firings.
Firing 1:
In the down-fire, there is one four hour hold at 1900 degF, followed by a four
hour hold at 1650 degF.
Firing 2:
In the down-fire, there is one four hour hold at 1650 degF, followed by a
four hour hold at 1900 degF.
The down-fire of Firing 2 reverses the order of the holds of the down-fire of
firing 1.
The bowls glazed with zincSr_Z3W_0 are ~6 inches in diameter. The bowls glazed
with
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 1900 deg F then a 4 hour hold at 1900 deg F
300 deg F an hour to 1650 deg F then a 4 hour hold at 1650 deg F
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 1650 deg F then a 4 hour hold at 1650 deg F
400 deg F an hour to 1900 deg F then a 4 hour hold at 1900 deg F
K2O 0.19
Al2O3 0.53
SiO2 3.08
molecular percent Silica 66.8%
Added:
2.5% Cobalt Carbonate
K2O 0.07
Al2O3 0.53
SiO2 2.55
molecular percent Silica 61.5%
The glaze zincSr_Z3W_0 in the first firing, with the hold at 1900 degF
preceding the hold at 1650 degF,
By contrast this glaze in the second firing, with the order of the holds
reversed, shows a strong
The defect near the bottom left of the bowl from the first firing was
caused by a kiln support
The glaze ironYellow in the first firing shows distinct green
micro-crystalline clusters,
that the order of the down-fire holds is a
relevant parameter, I fire this glaze in two firings with
only two
down-fire holds. In the second firing, the order of the down-fire holds is
reversed.
contrast glaze on the bisque before glazing the pot.
Image of the glaze zincSr_Z3W_0 in Firing 1
Image of the glaze zincSr_Z3W_0 in Firing 2
Image of the glaze ironYellow in Firing 1
Image of the glaze ironYellow in Firing 2
ironYellow are ~3 inches in diameter.
oxidation firing to cone 10 in an electric kiln
Firing profiles
Firing 1 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Firing 2 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze compositions
Empirical Formula zincSr_Z3W_0:
Na2O 0.28
CaO 0.02
MgO 0.19
SrO 0.14
ZnO 0.18
Empirical Formula ironYellow:
Na2O 0.11
CaO 0.81
MgO 0.01
Fe2O3 0.07
Remarks
shows a diffuse dusting of pink particles
over much of the glaze, with no strong pinks or strong blues.
segregation of the pink and blue crystals. There
is little of the pink to be seen, yet what there is is sharp,
and the
boundary between the pink crystals and the blue crystals is sharp. On
the outside,
the pink crystals, where not dense, are seen to have a nearly
cellular structure. This is the result of pink
micro-crystals filling in
between the large, deeply blue cobalt grains. The surface structure in the
second
firing is distinct.
accident in unloading.
and dark orangey-brown micro-crystals. In the
second firing, the green is gone, the micro-crystals are
yellow, with a
yellow matrix.