The effect of tin on a saturated iron glaze
Here are a pair of saturated iron glaze, satIron_ZG_Z3N_Z4A_0 and
satIron_ZG_Z3N_Z4A_0Sn;
Both of these glazes were fired with a slow up-fire, the second in a slower
firing than the first.
The effect of the addition of tin is dramatic. The leopard spots, and coppery
colored micro-crystal of
Tin reduces Fe2O3 to Fe2O, changes it from a weak network former to a network
modifier, i.e. to a flux.
400 deg F an hour to 1800 deg F
300 deg F an hour to 2050 deg F
200 deg F an hour to 2220 deg F with a 90 min hold at 2220 deg F
120 deg F an hour to 2320 degF
400 deg F an hour to 1800 deg F
300 deg F an hour to 2050 deg F
200 deg F an hour to 2220 deg F with a 90 min hold at 2220 deg F
90 deg F an hour to 2320 degF
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 hr hold at 1650 deg F
K2O 0.14
Al2O3 0.70
SiO2 3.65
molecular percent Silica 64.6%
K2O 0.14
Al2O3 0.70
SiO2 3.69
molecular percent Silica 63.5%
the addition of tin oxide to the first glaze
generated the second glaze. The change in empirical formula
is the
result of normalizing the recipe of the second glaze to 100, and replacing
red iron oxide with
yellow iron oxide.
I consider that to not have caused this result,
I report it for completeness.
satIron_ZG_Z3N_Z4A_0 are gone; what remains is
a homogenized brownish-purple glossy glaze.
The additional flux created in this manner
produced a less viscous glaze. The bubbles that formed
the leopard spots
in satIron_ZG_Z3N_Z4A_0 don't form, so don't grow the crystals on their
surface
which morphed into the leopard spots.
Image of the glaze satIron_ZG_Z3N_Z4A_0
Image of the glaze satIron_ZG_Z3N_Z4A_0Sn
bowls are ~6 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile one cone 10
Up Fire profile two 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_0Sn
Na2O 0.57
CaO 0.27
MgO 0.02
Fe2O3 0.23
P2O5 0.07
SnO2 0.11