Firing Saturated Iron Glazes
cone 10 oxidation with distinct downfire protocols
Firing #1 With a long hold at 1850 deg F
A three hour hold at 1850 deg F
One hour hold at 1650 deg F
Firing #2 With a long hold at 1800 deg F
half hour hold at 1850 deg F
A three hour hold at 1800 deg F
half hour hold at 1650 deg F
There is a 50 deg F difference between the temperature of the 3 hour soak in
these two firings.
I am Intrigued by the magnitude of that resultant change in the appearance
of the glazes.
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
Many of the bowls have a decorative leaf print within.
glaze composition
These glazes have high alkali metal, the numbers in the Empirical or Seger Formula:
Alkali metal ~.78
Li2O ~.2
molecular % silica 64 - 68
The major difference is Alumina varies from .44 to .65
The pots are smll conical bowls ~3 inches in diameter.
glaze satIron_ZG_1
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
glaze satIron_ZG_2
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
glaze satIron_ZG_4
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
glaze satIron_ZG_6
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
glaze satIron_ZG_7
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
glaze satIron_ZG_H_4
In Firing #1 with 3 hour hold at 1850 deg F
In Firing #2 with 3 hour hold at 1800 deg F
The primary difference seen with Firing #2 is an increase in the density of
the metallic crystals, and the crystal cluster size.
There is also a shift in the background color.
Additional shifts are seen in the number of
different colors and textures which are visible,
and in both the domain size
of the various colors, and their relative proportions.