Firing Saturated Iron Glazes

cone 10 oxidation with distinct downfire protocols

I show the results of firing two saturated iron glazes in 6 different firings.
Glazes which have prominent metallic crystals if fired with a slow downfire, didn't exhibit those crystals with the downfire replaced by a 3 hour soak at 1850 deg F.
I then moved the temperature of that long soak down by 50 deg, and got some crystals, and moving it further down got a few more.
Eventually I fired those glazes with no holds or soaks above 1750 to get lots of metallic crystals.
With the soak at 1850 in addition to the long soak and hold at 1700 deg F the crystals are present.
I have not as yet found a firing with only long holds that reproduces the first firing with the long slow downfire.

I concluded that the metallic crystals visible in these glazes grow at a temperature below 1800 deg F, and likely closer to 1750 deg F.

Below are the firing profiles, and pictures of the glazes in each firing.

Firing #1 With slow downfire in two intervals

A half hour hold at 1850 deg F
slow downfire at 50 deg F an hour in the interval 1850 deg F to 1700 deg F
slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F
half hour hold at 1650 deg F

Firing #2 With a long hold at 1850 deg F

A three hour hold at 1850 deg F
hour hold at 1650 deg F

Firing #3 With a long hold at 1800 deg F

half hour hold at 1850 deg F
A three hour hold at 1800 deg F
half hour hold at 1650 deg F

Firing #4 With a long hold at 1750 deg F

half hour hold at 1850 deg F
A three hour hold at 1750 deg F
half hour hold at 1650 deg F

Firing #5 With a long hold at 1850 deg F and at 1750 deg F

A three hour hold at 1850 deg F
A three hour hold at 1750 deg F
half hour hold at 1650 deg F

Firing #6 With a long hold at 1700 deg F

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
hour hold at 1650 deg F