Leopard Spots
I refer to a glaze which has dark spots on a light background as a
Leopard Spot glaze.
A leopard spot glaze satIron_mashiko_neph_1H_0 is shown here:
satIron_ZG_1S_1MMg, seen here, has a distinct composition and
appearance.
I show clos-ups of the spots and, for context, a picture of the pot.
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
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
K2O .16
Al2O3 .53
SiO2 3.27
molecular percent Silica 63%
Although this glaze, satIron_ZG_1S_1MMg, and the prior glaze
satIron_mashiko_neph_1H_0 show dark spots on a light background,
Dark spots on a light background is a particular form of phase separation in
the liquid melt at the point when the liquid solidifies.
Leopard spots are not easily reproducible, as small changes in the firing
protocol, or glaze application thickness can reduce
Close up Images of the spots
Image of the piece
bowl with glaze satIron_ZG_1S_1MMg
small bowl ~4 inches in diameter
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 composition
Empirical Formula satIron_ZG_1S_1MMg :
Na2O .41
Li2O .21
CaO .21
MgO .01
Fe2O3 .2
P2O5 0.18
Remarks
the two
glazes are not similar in appearance; the spots on SatIron_ZG_1S_1MMg are
raggedy, and the background is
metallic and gold colored. This is not
surprising as these two glazes have little in common other than high Iron,
equal silica:alumina ratio, and high phosphorus.
It is a kind of
behavior of the melt, which is not specific to a particular composition.
the size of the spots
to near invisibility.