The effect of More phosphorus
The next step, a substantial increase in phosphorus, to .2 molecular
equivalents, with a reduction of the silica by that amount.
I used ferrous phosphate to allow high phosphorus without the high calcium
that results from the use of Bone Ash
I thank Hank Murrow for suggesting this experiment and providing the
required ferrous phosphate.
This is the same firing protocol as used for the precursor glaze.
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
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
The glaze with .2 molecular fraction Phosphorus
K2O .1
Al2O3 .6
SiO2 2.95
molecular percent Silica 60%
inside of bowl:
Outside of bowl:
the glaze on the inside of the bowl exhibits a
dense cover comprised of metallic gold micro-crystals where
The dark non-sparkly parts on the inside of the bowl are an artifact of
the surface geometry -
The glaze on the outside of the bowl is thinner, perhaps half the thickness of
the glaze on the inside. There is a sparse dusting of
With this much phosphorus in the glaze, the non-crystalline part of the glaze
is mostly orang-y brown rather than black.
The replacement of some silica with Phosphorus seems to have effected
neither the fluidity of the glaze nor its surface texture;
as a phosphate source.
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula glaze satIron_ZG_0PP :
Na2O .48
Li2O .2
CaO .16
MgO .06
Fe2O3 .2
P2O5 .2
Glaze satIron_ZG_0PP
bowl is ~3 inches in diameter
Remarks
the glaze is
thickly applied. There is no background glaze visible on most of the
inside of the bowl. Its appearance is that of a crumpled mirror.
The micro-crystals that are angled away from the light
do not appear reflective in photographs.
metallic gold crystals,
not visible in the photograph.
it remains a
textured gloss. This is consistent with the fact that phosphorus is a glass
former, though it might be
a more refractory glass former than silica.