Breaking Colors - Leopard Spots
The glaze leopard_Z1T has two predominant colors, a lusterous brown-black, and
a metallic gold speckled orangy-brown.
The glaze leopard_Z1T is the third in a series of glazes, the first two of
which were leopard_Z1R, followed by leopard_Z1S.
I show close-ups of the spots and markings of the glaze leopard_Z1T and, for
context, a picture of the pot.
Images of the two preceding glazes in the series, leopard_Z1R and
leopard_Z1S are shown to give an indication of the
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
K2O .06
Al2O3 .76
SiO2 4.12
molecular percent Silica 65%
K2O .06
Al2O3 .66
SiO2 4.3
molecular percent Silica 67%
K2O .1
Al2O3 .76
SiO2 4
molecular percent Silica 64%
The first glaze in this series, leopard_Z1R has a bronze colored
background with metalic micro-crystals and dark spots.
The next glaze in the series, leopard_Z1S, is a lusterous brown-black. It has
prominent pinholes as a result of its high viscosity
The composition of leopard_Z1S differs from that of leopard_Z1R by having
higher alkali metals and higher alumina.
The third glaze in the series, leopard_Z1T has large high contrast spots in a
matrix of metallic speckled orange brown. It also has high viscosity
The composition of the glaze leopard_Z1T is a cross between leopard_Z1R and
leopard_Z1S. It has the bases of leopard_Z1R
As these two colors are sharply
delineated from each other, I call this a breaking color. It is also
a leopard spot glaze as it has
dark spots on a light background, though some
of the spots merge.
influence of compositional
variations in this particular glaze family.
Close-up Images of the markings on leopard_Z1T
Image of the piece
image of predecessors
bowl with glaze leopard_Z1R
bowl with glaze leopard_Z1S
all pieces shown are small bowls ~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 compositions
Empirical Formula leopard_Z1T :
Na2O .40
Li2O .19
CaO .34
MgO .01
Fe2O3 .26
P2O5 0.17
Empirical Formula leopard_Z1R :
Na2O .38
Li2O .2
CaO .34
MgO .02
Fe2O3 .28
P2O5 0.16
Empirical Formula leopard_Z1S :
Na2O .42
Li2O .21
CaO .25
MgO .02
Fe2O3 .27
P2O5 0.17
Remarks
The dark spots
are small and easily missed
and thick glaze
application.
Some of the CaO was replaced by
alkali metals. then the molecular fraction of alumina was raised to retain
the same value for the
alkali metal:alumina ratio, as that of
leopard_Z1R.
so crawls readily.
(i.e. the higher CaO and lower
alkali metals); as well as the higher alumina of leopard_Z1S.