Effects of Firing
I show the effect of two different firing protocols on a glaze with metallic
surface crystals.
My previous work showing the effect of slowing the firing above 1900 deg F:
The first firing has slowed cooling for temperatures above 1900 deg F and
slightly below turn-down. This firing spends ~4 hours in this region.
The second firing is a control: it is allowed to cool normally, spending only
~ an hour and a half in the temperature region above 1900 deg F.
The metallic surface crystals are micro-crystals, as are the
red/yellow/orange dendritic-like patterns.
The grey splotches are silvery metallic crystals.
The leaf pattern on the glaze is created by embedding a leaf in the wet glaze,
waxing with an emulsion when dry, then removing the leaf
The Both firings have the same Up Fire Profile, which is given here:
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
There are two distinct down-fire protocols, given here:
300 deg F hr to 2210 deg F then hold 30 minutes
80 deg F hr to 1900 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 Two hour hold at 1700 deg F
300 deg F an hour to 1600 deg F then a two hour hold at 1600 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
300 deg F an hour to 1600 deg F then a two hour hold at 1600 deg F
K2O .03
Al2O3 .63
SiO2 4.17
molecular percent Silica 67%
slow cooling from below top to 1900 deg F.
Inside of pot:
slow cooling only below 1750 deg F
Inside of pot:
The glaze that was cooled slowly above 1900 deg F, shows more varied colors, a
variety of oranges and reds, and substantially greater formation
The slow cooling in a region
where crystal growth is rapid facilitated the growth of
large coarse
crystals.
and coating the
exposed area with a thinned glaze or oxide wash.
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile 1
Down Fire Profile 2
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze composition
Empirical Formula glaze satIronZT_MashikoCNeph_Z1I :
Na2O .16
Li2O .2
CaO .44
MgO .17
Fe2O3 .25
P2O5 .14
First Firing
Second Firing
bowls are ~ 4inches, resp 6 inches in diameter
Remarks
of
metallic surface micro-crystals.
In the faster cooled glaze, the
background color is more uniform and has shifted to a yellower lighter hue.