Effects of Firing

I show the effect of two different firing protocols on a glaze with metallic surface crystals.

One of these firing has slowed cooling for temperatures above 1900 deg F and slightly below turn-down.
My kiln will normally cool to 1900 deg F in ~ an hour and a half. Instead, in the first firing, the time in this
interval is increased to ~ 4 hours. The second firing is a control: it is
allowed to cool normally, the slow ramps and holds are below 1750 deg F.

The metallic surface crystals are micro-crystals, as likely are the red/yellow/orange dendritic-like patterns.
The slow cooling in a region where crystal growth is rapid facilitated the growth of
large coarse crystals.

This glaze with slow cooling above 1900 deg F shows more metallic surface micro crystals and greater range of colors.

The leaf pattern on the glaze is created by embedding a leaf in the wet glaze, waxing with an emulsion was when dry, then removing the leaf
and coating the exposed area with a thinned glaze or oxide wash.

oxidation firing to cone 10 in an electric kiln

Firing profiles

Both firings have the same Up Fire Profile, which is given here:

Up Fire profile

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:

Down Fire Profile 1

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

Down Fire Profile 2

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

Clay body is a grolleg porcelain from Tacoma Clay Art Center.

glaze composition

Empirical Formula glaze satIron_ZT_MashikoLi_1H_1J :

K2O        .01
Na2O        .01
Li2O        .25
CaO        .45
MgO        .28

Al2O3        .49
Fe2O3        .2

SiO2        3.35
P2O5        0.15

molecular percent Silica 65%

First Firing

slow cooling from below top to 1900 deg F.

Inside and outside of pot:

Second Firing

slow cooling only below 1750 deg F

Inside of pot:

bowls are ~ 6 inches in diameter

Remarks

The glaze that was cooled slowly above 1900 deg F, shows more varied colors, a variety of oranges and reds, and substantially greater formation
of metallic surface micro-crystals.
In the faster cooled glaze, the background color is more uniform.

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