Leopard Spots again
The first glaze, satIron_ZG_Z3N_Z4A_0 is a bright glossy glaze with a hint of
coppery colored
The second glaze, satIron_ZG_Z3N_Z4A_1, even brighter and glossier, yet the
leopard spots are now
The second glaze has slightly lower alkali metals, higher calcia than the
first, and slightly
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 1850 deg F then a 2 hr hold at 1850 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
300 deg F an hour to 1700 deg F then a 3 hr hold at 1700 deg F
25 deg F an hour to 1650 deg F then a 1 hour hold at 1650 deg F
K2O 0.14
Al2O3 0.70
SiO2 3.65
molecular percent Silica 64.61%
K2O 0.14
Al2O3 0.70
SiO2 3.38
molecular percent Silica 62.8%
The second glaze, satIron_ZG_Z3N_Z4A_1 with higher CaO, had larger leopard
spots than the first
In our previous
note: the glaze with higher CaO and lower alkali metals had larger and
more
If indeed the leopard spots are as I conjecture the result of
micro-crystalline growth
Then the density of the color of the leopard spots will be a function of the
amount of crystal formation
I suspect that the second glaze in this note, satIron_ZG_Z3N_Z4A_1, with lower
silica has, as a result,
The first glaze in the prior note, satIron_ZG_Z3N_EPK, with a glossier
surface, is likely less
micro-crystals and large leopard spots, black and
fragmented as if a broken open orange peel.
reduced to only the outline of a disk, a circle of
reddish brown dots.
lower silica. Small shifts in alkalis and silica, and
only a ghost of the leopard spots remain.
Image of the glaze satIron_ZG_Z3N_Z4A_0
inside
outside
bowl is ~3.5 inches in diameter
Image of the glaze satIron_ZG_Z3N_Z4A_1
inside
outside
bowl is ~3.5 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile cone 10
Down Fire Profile cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze compositions
Empirical Formula satIron_ZG_Z3N_Z4A_0 :
Na2O 0.56
CaO 0.28
MgO 0.02
Fe2O3 0.23
P2O5 0.07
Empirical Formula satIron_ZG_Z3N_Z4A_1 :
Na2O 0.53
CaO 0.31
MgO 0.02
Fe2O3 0.22
P2O5 0.08
Conjecture re the driving force for leopard spot formation
glaze, satIron_ZG_Z3N_Z4A_0. Yet these larger
leopard spots are ghostly, like the cheshire cat,
on the verge of
disappearing.
impressive leopard spots.
on the inside of bubbles, which pop at the surface,
then larger bubble lead to larger leopard
spots. Perhaps higher CaO results
in larger bubbles.
within the bubble, on its surface, before it
reaches the surface to pop. If the viscosity of the glaze
is low, the bubble
reaches the surface quickly with little micro-crystalline growth.
lower visosity, giving the internal bubble surface
little time to grow crystals. That it is less viscous
perhaps leads to less
surface crystal growth of the matrix glaze, so a glossier surface.
viscous than the second glaze in that note,
satIron_ZG_Z3N_Z4A_2, so perhaps bubbles rise
faster, with less micro-crystal
development on the internal bubble surface.