Viscosity vs Gloss
cone 10 oxidation
Firing profile
Up Fire profile
150 deg F an hour to 250 deg F
400 deg F an hour to 2050 deg F
120 deg F an hour to 2250 deg F
60 deg F an hour to 2290 deg F
40 deg F an hour to 2310 deg F with a hold of 10 minutes at 2310 deg F
Down Fire 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.
I show a leaf print on two saturated iron glazes of differing viscosity
glaze composition
Emperical Formula satIron_ZJ_1PP:
K2O 0.01
Na2O 0.47
Li2O 0.23
CaO 0.23
MgO 0.06
Al2O3 .47
Fe2O3 .19
SiO2 2.93
P2O5 .07
molecular percent Silica 63 %
Emperical Formula satIron_ZJ_2:
K2O 0.09
Na2O 0.48
Li2O 0.26
CaO 0.15
MgO 0.02
Al2O3 .56
Fe2O3 .19
SiO2 3.49
P2O5 .04
molecular percent Silica 66 %
discussion of composition
The glaze, satIron_ZJ_1PP has lower alumina and lower silica than the second
glaze satIron_ZJ_2.
The first glaze has less silica, and less alumina, as
a percent of the oxides in the glaze, unormalized by the fluxes.
The
result is a glaze which is less viscous.
Both pots are plates approximately 9 inches in diameter. The leaf print is
created by embedding a leaf in the wet glaze,
then after dry, staining with a
mixture of Feldspar and rutile, or Kaolin and rutile.
glaze satIron_ZJ_1PP
glaze satIron_ZJ_2
Discussion
The leaf print on the glaze satIron_ZJ_1PP is an
undifferentiated blob, I could have achieved a similar result
by randomly
dribbling stain on the glaze. The glaze satIron_ZJ_1PP flowed
beneath the leaf
obliterating the details, texture and leaf veins, mixing
all together.
By contrast satIron_ZJ_2 hardly moves, leaving undisturbed the leaf structure, its veins and the ruckled undulating surface of the leaf.
Both glazes have fully gloss surfaces. Though satIron_ZJ_2 is the glossier
of the two glazes, with the smoother less textured surface,
nevertheless it is
cleary the more viscous glaze.
The surface texture
of a glaze is independant of its viscosity, i.e. of how readily it flows.
Both of these glazed show a variety of metallic surface crystals, all high in iron.
In any region one sort of crystal will dominate
as the various
crystals compete for the limited supply of iron. The glaze thickness
determines which type of crystal grows fastest,
and also the grain size of
the crystals grown.
Distinct crystals are often found in rings marking
the thickening of the glaze from rim to bottom
characteristic of glaze
applied by pouring into
a bowl shape.