Firing time vs. temperature
I show the difference between two firing profiles on a saturated iron glaze: a
slow, colder firing, versus a fast hot firing.
The slow colder firing has more time in the approach to cone 10, a lower
firing temperature and longer holds in the cool-down profile.
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,
fast firing to cone 10 at 2310 deg F.
Inside of pot:
Outside of pot:
slow firing to cone 10 at 2210 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, 2210 deg F for the second.
The temperature ramp is steeper for the first firing, slower for the second.
Faster and hotter:
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 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 1770 deg F
300 deg F an hour to 1850 deg F
120 deg F an hour to 2130 deg F
13 deg F an hour to 2180 deg F / hold 2 hr
13 deg F an hour to 2210 deg F / hold 3 hr
300 deg F an hour to 1900 deg F then hold 3 hours
300 deg F an hour to 1850 deg F then hold 3 hours
K2O .05
Al2O3 .5
SiO2 3.26
molecular percent Silica 65%
This glaze in my usual firing is a lusterous full gloss, with orange and red
markings in a tan matrix. Additionally, there are
In the variant firing, to a lower temperature with a slower ramp, it is a full
gloss, dark purple-brown where thick,
Interestingly, this glaze is significantly more fluid and, consequently,
drippier in the lower temperature, slower firing.
the second slower but only to 2210 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 iron_8_R_165_5PP_M :
Na2O .41
Li2O .2
CaO .2
MgO .14
Fe2O3 .2
P2O5 .05
bowls are ~ 4 inches in diameter
Remarks
metallic silvery particles,
particularly where the glaze is thick. This is seen in the first pictures.
else it exhibits intermixed
striations of iron red and a mustardy yellow. This is seen in the second set
of pictures.