More Firing temperature vs. Time
I show the effect of more time above cone 5 together with lower firing temperature
on a saturated iron glaze.
Previously I'd shown that contrast
Now I show a different glaze in two cone 10 firings.
The first firing is to 2310 deg F,
faster firing to cone 10 at 2310 deg F.
Inside of pot:
Outside of pot:
slower firing to cone 10 at 2270 deg F
Inside of pot:
Outside of pot:
The differences between the first and second upfire profiles are:
The top temperature, 2310 deg F for the first, 2270 deg F for the second.
The temperature ramp is steaper for the first firing, slower for the second.
Faster and hotter:
150 deg F an hour to 200 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
Slower and cooler
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 2170 deg F
15 deg F an hour to 2270 deg F / hold 20 min
300 deg F an hour to 1850 deg F then hold 3 hours
300 deg F an hour to 1600 deg F then a Three hour hold at 1600 deg F
K2O .01
Al2O3 .46
SiO2 2.92
molecular percent Silica 63%
This glaze in my usual firing is a waxy matte, and has a near dense coverage
of metallic microcrystals. It's mixed reds and black, and has no tan.
In the variant firing, to a lower temperature with a slower ramp, it is a full
gloss, dark brown, and has only scattered metallic microcrystals,
The hold at 1600 deg F is present as required by those glazes for the
development of the metallic micro-crystals.
Next is an even slower ramp to cone 10, with a lower final firing temperature.
the second slower but only to 2270 deg F.
First Firing
Second Firing
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile 1
Down Fire Profile 1
Up Fire profile 2
Down Fire Profile 2
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze composition
Empirical Formula glaze satIron_ZG_H_1 :
Na2O .52
Li2O .23
CaO .17
MgO .07
Fe2O3 .2
P2O5 .05
bowls are ~ 4 inches in diameter
Remarks
This is seen in the first pair of pictures
as seen
in the second pair of pictures. It flows sufficiently to have dripped
onto the kiln shelf.
I attribute the decrease in
metallic micro-crystals to the lower final firing temperature, though the
slower temperature ramp may be relevant as well.