The effect of distinct Firings on a Glaze
The glaze satIron_ZG_1S_Z3J seen in two distinct firing protocols; both
firings have the same up-fire
Previously . this glaze was seen in two firings, which differed in both
the up-fire and down-fire,
As can be seen here, the difference in down-fire protocol changed the glaze,
but did not produce oil spots.
The primary difference in the down-fire profiles is a hold of two hours at
1800 deg F in the first firing, which
This glaze in the second firing, without the hold at 1800 deg F, is darker
with black and orange markings.
It is interesting that there are three different firings represented, and the
appearance of this glaze
The inlay design in the bowl in the first firing is
glazed with inlay_Z3K.
The design is created by adhering a mask and then applying the main
glaze. After drying,
Inlay glaze is inlay_Z3K_0
bowl is ~5 inches in diameter.
bowl is ~4 inches in diameter.
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 1800 deg F then a 2 hr hold at 1800 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
50 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
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 4 hour hold at 1750 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.33
Al2O3 0.50
SiO2 3.4
molecular percent Silica 64.7%
K2O 0.14
Al2O3 0.58
SiO2 2.31
molecular percent Silica 56.5%
protocol, and differ only in the down-fire.
so that attributing the oil spots to the
difference in up-fire protocol was questionable.
The appearance of the oil spots seen in
the first firing in the prior note can now with more confidence be
attributed to the change in the up-fire protocol.
is missing in the second firing. The
second firing has a longer hold at 1750 deg F which had been intended to
compensate for the lost hold at 1800 deg F.
It also has a prominent dusting of
coppery colored metallic micro-crystals. These micro-crystals also appear
in
the orangy glaze in the first firing, but lesser contrast decreases
their prominence.
differs in each.
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 satIron_ZG_1S_Z3J in Firing One
Image of the glaze satIron_ZG_1S_Z3J in Firing Two
oxidation firing to cone 10 in an electric kiln
Firing profiles
First Firing
Up Fire profile Firing 1
Down Fire Profile Firing 1
Second Firing
Up Fire profile Firing 2
Down Fire Profile Firing 2
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze composition
Empirical Formula satIron_ZG_1S_Z3J:
Na2O 0.48
CaO 0.18
MgO 0.01
Fe2O3 0.17
P2O5 0.17
Empirical Formula inlay_Z3K_0 :
Na2O 0.82
CaO 0.02
MgO 0.02
Fe2O3 0.02
P2O5 0.18