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 in a cone 10 firing:

June 2019 Cone 10 Yet More Firing Effects

Here I show the effect of lowering the firing temperature.

The first firing is a hot cone 10 with cone 11 tipped and almost at 10 oclock.

The second firing is a middle cone 10.

The look of my cones had migrated. This is an attempt to recover my original firing.

The metallic surface crystals are micro-crystals: as are the red/yellow/orange dendritic-like patterns.
The lower top temperature allows micro-impurities in the glaze melt to remain after the kiln starts down.
These are sites for crystal formation.

As the micro-crystals form well below the top temperature of the firing, it is possible that the effect of lowering that temperature can nearly
match the effect of slowing the down firing above 1900 deg F. However one must then test the effect of both lowering the final
firing temperature and slowing the downfiring above 1900 deg F. This reproduces the sort of firing we had in hard-brick kilns.

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
and coating the exposed area with a thinned glaze or oxide wash.

oxidation firing to cone 10 in an electric kiln

Firing profiles

The difference between the first and second upfire profiles is the top temperature, 2310 deg F for the first, 2300 deg F for the second

Up Fire profile 1

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:

There are two distinct down-fire protocols. Both had distinctive holds below 1700 deg F. This information is included for completeness,
but I do not consider the differences below 1700 deg F relevant for this glaze.

Down Fire Profile 1

300 deg F hr to 2210 deg F then hold 30 minutes

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
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F

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

glaze composition

Empirical Formula glaze satIronZT_MashikoCNeph_Z1I :

K2O        .03
Na2O        .16
Li2O        .2
CaO        .44
MgO        .17

Al2O3        .63
Fe2O3        .25

SiO2        4.17
P2O5        .14

molecular percent Silica 67%

First Firing

Hot cone 10, nearly cone 11

Inside of pot:

Second Firing

lower top temperature

Inside of pot:

Outside of pot:

bowls are ~ 6 inches, resp 4 inches in diameter

Remarks

The glaze that was fired to a lower top temperature, shows more varied colors: a variety of oranges and reds, and substantially greater formation
of metallic surface micro-crystals.
In the hotter fired glaze, the background color is more uniform and has shifted to a yellower and lighter hue.

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