Phosphorus Redux

cone 10 oxidation

Firing profile

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 2250 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

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

Previously tested high phosphorus glazes:

iron and phosphorus

glaze thickness in high phosphorus glazes

Even higher phosphorus

We last saw satIron_ZT_0 which had P2O5 of .24. If bone ash is the source of the P2O5 CaO will be ~ 3 times the P2O5,
this makes CaO ~ .72. So P2O5 ~.24 is a practical limit on Phosphorus in a glaze containing ~ .3 alkali metal bases (fluxes).

Here we show two more glazes with P2O5 ~.24. They contain higher Alumina, and lower silica than satIron_ZT_0.

In addition to the silvery microcrystalline film, there are clusters of metallic garnet micro-crystals.
In places the microcrystals are sufficiently dense as to coalesce into a continuous metallic film resembling
colored aluminum foil.

The prominence of metallic surface film vs the glossy/matte base layer is determined by the angle of the incident light.
The color of the metallic surface film also changes with the light angle. These pictures are all taken with a ring light,
so the light angle is different inside/outside of the pot, which emphasizes the slight differences between inside and outside of the pots.

The first two glazes shown, satIron_ZT_V_0 and satIron_ZT_W_1 have the same empirical formula, satIron_ZT_V_0 has a purple semimatte background
and the microcrystalline surface layer is dense, this difference in appearance is the result of the thicker glaze application of satIron_ZT_V_0.

satIron_ZT_W_0 has higer silica than satIron_ZT_W_1.