Phosphorus

Phosphorus in small concentrations facilitates the growth of metallic micro-crystals. Yet in larger concentrations, it eliminates them.

Perhaps there is an optimal level of phosphorus for the growth of metallic micro-crystals?

In the previous

HIGH-phosphorus test

full view

the glaze satIron_ZG_1S_1MMg

exhibits leopard spots, but few metallic micro-crystals.

In the previous

LOW-phosphorus test

the glaze satIron_ZG_1O_0 exhibits metallic micro-crystals, but no leopard spots.

full view

bowl with glaze satIron_ZG_1O_0

In the current test, satIron_ZG_1S_1MMgP has a phosphorus level between the two previous tests, although it is closer to satIron_ZG_1O_0.
As expected, this small increase in phosphorus and the lack of magnesium nearly eliminate the metallic Micro-crystals.
This is the glossy orange-y background glaze in the upper right.

The glaze in the lower left, satIron_Z1W_0 has low phosphorus and higher magnesium, and has small dense metallic micro-crystals.

The pattern is created created by adhering a mask and then applying the main glaze. After drying,
the entire pot is coated in wax, then the mask is removed and the open area filled in with a second glaze.

That background is a different test glaze satIron_Z1W_0.

Image of the piece

full view

plate with glaze satIron_ZG_1S_1MMgP upper right, lower left is satIron_Z1W_0

plate ~8 inches in diameter

oxidation firing to cone 10 in an electric kiln

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 2310 deg F with a hold of 20 minutes at 2310 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.

glaze composition

Empirical Formula satIron_ZG_1S_1MMg :

K2O        .16
Na2O        .41
Li2O        .21
CaO        .21
MgO        .01

Al2O3        .53
Fe2O3        .2

SiO2        3.27
P2O5        0.18

molecular percent Silica 63%

Empirical Formula satIron_ZG_1S_1MMgP :

K2O        .16
Na2O        .42
Li2O        .19
CaO        .21
MgO        .02

Al2O3        .53
Fe2O3        .2

SiO2        3.21
P2O5        .05

molecular percent Silica 64%

Empirical Formula satIron_Z1W_0 :

K2O        .19
Na2O        .31
Li2O        .23
CaO        .17
MgO        .1

Al2O3        .54
Fe2O3        .24

SiO2        2.91
P2O5        .04

molecular percent Silica 61%

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