Firing profiles and their effect on glaze texture

Then I displayed the result of a slower, cooler firing on a semi-matte iron free glaze in two cone 10 firings

Now, I exhibit one glaze in four different cone 10 firings of varying lengths, with distinct final temperatures.
The three slower firings have holds at different temperatures both in the up-fire and down-fire part of the firing cycle.

I developed these firing profiles using the Orton Cone prediction calculator, formerly available on the Orton Foundation Web Page.

For the last firing, I also display this glaze on a different clay body.

Firing One

faster firing to cone 10 at 2310 deg F.

Inside of pot in grolleg porcelain:

bowl is ~ 4 inches in diameter

Firing Two

slower firing to cone 10 at 2230 deg F

Inside of pot in grolleg porcelain:

bowl is ~ 4 inches in diameter

Firing Three

slower firing to a low cone 10 at 2190 deg F
This firing has longer holds in the up-firing than Firing 2 above.

Inside of pot in grolleg porcelain:

bowl is ~ 6 inches in diameter

Firing Four

slower firing to cone 10 at 2220 deg F
This firing has long holds in the up-firing and longer holds in the down-fire as well.

Inside of pot in grolleg porcelain:

bowl is ~ 4 inches in diameter

To show the effect of the clay body, here is this glaze on a different clay, crystal springs porcelain:

free form slab is ~ 4 inches in diameter

oxidation firing to cone 10 in an electric kiln

Firing profiles

The differences between the first fast firing and the other three firings is primarily in the top temperature reached, and the lengths
of the holds getting to that top temperature.

The top temperature, 2310 deg F for the first, 2230 deg F for the second, 2190 deg F for the third, and 2220 deg F for the fourth.

The temperature ramp is steeper for the first firing, slower for the others.

Up Fire profile 1

Faster and hotter:

150 deg F an hour to 250 deg F

400 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

Down Fire Profile 1

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

Up Fire profile 2

Slower and cooler

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 2150 deg F

13 deg F an hour to 2200 deg F / hold 1 hr

13 deg F an hour to 2230 deg F / hold 1 hr

Down Fire Profile 2

300 deg F an hour to 1900 deg F then hold 2 hours

300 deg F an hour to 1850 deg F then hold 2 hours

Up Fire profile 3

Slower and cooler

150 deg F an hour to 250 deg F

400 deg F an hour to 1770 deg F

40 deg F an hour to 2130 deg F

13 deg F an hour to 2150 deg F / hold 4 hr

13 deg F an hour to 2170 deg F / hold 2 hr

13 deg F an hour to 2190 deg F / hold 2.5 hr

Down Fire Profile 3

300 deg F an hour to 1900 deg F then hold 2 hours

300 deg F an hour to 1850 deg F then hold 2 hours

Up Fire profile 4

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 1860 deg F

120 deg F an hour to 2140 deg F

13 deg F an hour to 2190 deg F / hold 2 hr

13 deg F an hour to 2220 deg F / hold 2 hr

Down Fire Profile 4

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

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

Clay body for slab is a crystal springs porcelain from Georgies.

glaze composition