oil spot glazes
firing to cone 10 in oxidation
The Downfire 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.
The glaze mashikoKaki_3PLiMSi has a lusterous glossy mirror like metallic
surface punctuated with large high contrast oil spots.
The flaw, the
dimples in the oil spots, technically known as "cats eyes".
the glaze mashikoKaki_3PLiMSi is seen here:
I show some variants of this glaze in which the cat eyes defect is much
reduced.
These glaze have high contrast oil spots and while lacking the
full gloss background of mashikoKaki_3PLiMS,
have a burnished metal
ground which is as interesting as the full gloss of mashikoKaki_3PLiMSi.
glaze composition
MashikoKaki_3PLiMSi is high in alkaline earths, with Al2O3 = .8, SiO2 = 5.67,
alk:alumina ratio of .4 and Silica:alumina ratio of 7, mol percent silica
73%.
The variants are higher in MgO and lower in CaO.
They differ from each other in fraction of CaO vs alkali metals, and in the
balance
of the alkali metals.
Silica, alumina and iron remain as in
mashikoKaki_3PLiMSi.
The pots are small bowls ~4 inches in diameter.
mashiko_ZJ_0
mashiko_ZJ_1
mashiko_ZJ_2
mashiko_ZJ_3
Commentary
The surface of all of these glaze is microcrystalline, with glossy microcrystals,the result is these glaze have a mirror like reflectivity which appears fuzzy.
The alkali metal to alkaline earth ratio varies from .4 to .7, a more
substantial difference
in the glaze composition than is seen in the fired
results,
which seem to differ primarily in the sheen of the background to
the oil spots.