Phosphorus

Firing profiles

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 2300 deg F with a hold of 20 minutes at 2300 deg F

Down Fire Profile

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.

Empirical Formula glaze satIron_ZG_1U_0PP :

The glaze with .07 molecular fraction Phosphorus

K2O        .23
Na2O        .32
Li2O        .22
CaO        .06
MgO        .17

Al2O3        .47
Fe2O3        .19

SiO2        3
P2O5        .07

molecular percent Silica 63%

Remarks

The glaze satIron_ZG_1U_0PP if sufficiently thickly applied, as it is on the inside of the bowl, is a mixture of a range of colors,
among which are blacks, greens, oranges and yellows. There are also flecks of metallic silvery particles.
It appears to be opaque, which is an illusion created by its thickness. Its apparent vibrancy, is created by the paint spatter
effect of close proximity of distinct hues.

If applied thinly, as on the outside of the bowl, it's a translucent nondescript yellow-brown, with some hint of color range
in the red splotches on a mustard background.

The source of the P2O5 is Trisodium phosphate, allowing lower CaO than would be possible in a glaze containing bone ash as the phosphate source.

Perhaps as a result of low CaO / higher MgO, this glaze is more viscous than might be expected for such high alkali metals.
That higher viscosity makes movement within the glaze slow and facilitated the growth of a variety of distinctive micro-crystals.