Microcrystalline saturated Iron glaze

firing to cone 10 in oxidation

Firing profile #1

Up Fire profile

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

A half hour hold at 1750 deg F

A three hour hold at 1700 deg F

slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F

A one hour hold at 1650 deg F

Firing Profile #2

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 2050 deg F

120 deg F an hour to 2240 deg F

60 deg F an hour to 2290 deg F

30 deg F an hour to 2300 deg F with a hold of 20 minutes at 2300 deg F

Down Fire Profile

A half hour hold at 1750 deg F

A three hour hold at 1700 deg F

slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F

A one hour hold at 1650 deg F

Firing Profile #3

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 2050 deg F

120 deg F an hour to 2240 deg F

60 deg F an hour to 2290 deg F with a hold of 15 minutes at 2290 deg F

60 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 deg F

Down Fire Profile

A half hour hold at 1750 deg F

A three hour hold at 1700 deg F

slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F

A one hour hold at 1650 deg F

discussion of firing profiles

Above are the firing profiles as one would program the electronic Kiln Controller
The downfire part of these protocols, the part of the firing after peak temperature is reached,
is the same for all three firing protocols.
For that reason, and to simplify a discussion of the differences between these three firing profiles,
they are separated into Up, and Down.

In both the second and third firing protocol The "sharp peak" at the top of the firing curve is smoothed down.
The objective is to flatten the top of the firing, slow it down to enable
the many chemical processes within the glaze and body to catch up with each other.

The objective is to find a firing method which gives similar results on thin and thick pots
for a saturated iron glaze, while maintaining the appearance of the glaze seen on
thin walled test pots fired with Firing Profile #1.

In smoothing the top of the firing curve in the region above 2240 deg F, I subdivided that region
into three regions which I consider to successively contribute more heat work to the final cone achieved in the firing.
These regions are: 2240 to 2290 deg F, 2290 deg F - 2310 deg F, above 2310 deg F

Here is a table showing the amount of time spent in each of these regions following the three firing profiles given above:

Time in temperature window

	2240-2290 deg F	2290-2310 deg F	greater than 2310    deg F
firing 1	21.5 min	10 min	20 min
firing 2	50 min	40 min	0 min
firing 3	41 min	35 min	20 min

Comparing both firings with Firing #1, Firing #2 spends more time in the regions 2240-2290 deg F,
and region 2290-2310 deg F, but less time at or above 2310 deg F.
It is a bit less than half a cone cooler than Firing #1.

Firing #3 also spends more time in regions 2240-2290 deg F, and 2290-2310 deg F, and equal time at or above 2310 deg F.
It is a bit less than half a cone hotter than Firing #1.

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