The effect of distinct Firings on a Glaze
The glaze satIron_ZG_1S_Z3J seen in two distinct firing protocols.
Both firings are to Cone 10 in an electric Kiln, though the first
firing is a hot cone 10,
The first firing is slowed on the way up with an hour hold at 2170 deg F, and
an additional half-hour hold at
The intent had been to increase the time available for slower reacting
materials to enter the glaze melt,
The second firing was comprised of a much faster ramp up, but holds on the way
down at 1750 deg F, 1700 deg F,
It is interesting that the result of increasing the total firing time and
adding holds near the top temperature
The holds on the way down in the first firing differ as well, an artifact of
the inconvenience of programming
The inlay design in the bowl in the second firing is
glazed with inlay_Z3K.
The design is created by adhering a mask and then applying the main
glaze. After drying,
bowl is ~ 4 inches in diameter.
bowl is ~5 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 2170 deg F with a hold of 1 hour at 2170 deg F
120 deg F an hour to 2250 deg F
60 deg F an hour to 2270 deg F with a hold of 30 minutes at 2270 deg F
60 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
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
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%
with the cone 11 slightly more than tipped.
2270 deg F. In addition, it has a slower
temperature rise for the last segments of the up part of the firing.
without firing to a higher cone. This
result was only partially achieved.
and 1650 deg F. In the second firing, the
glaze is orangy-brown, with a dusting of metallic coppery colored
particles.
In the bottom where the glaze is a bit thicker is seen a thin
broken black outline of a hexagonal
cellular structure.
seems to have been to create an oil
spot glaze in the first firing. One is tempted to imagine that the faint
outline of a cellular structure visible in the bottom of the bowl fired
fast, in the second firing, grew
into the dominant black matrix of the
oil spot glaze, while the interiors of the cells shrunk to the visible
oil spots seen in the first firing.
more than 8 ramps for the kiln
controller. I doubt that the difference in holds at a low
temperature are
relevant to the formation of an oil spot glaze.
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
inside
outside
Image of the glaze satIron_ZG_1S_Z3J in Firing Two
Inlay glaze is inlay_Z3K_0
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