The Two modes of a Gaze
This glaze can appear as a micro-crystalline matte glaze, or a variegated
glossy iron red with
multitudinous crystals, depending on its mood.
There may be two factors (or more) that contribute to the variation in the
appearance of this glaze:
the application thickness, and the clay base to
which it adheres.
A porcelain mug, which is not shown, has the glossy variegated version of this
glaze on the exterior,
but has almost the micro-crystalline matte version
on its inside bottom where the glaze pooled. That mug is
the same clay as
the bowl that is displayed below, and from which I conclude that the
dense crystals of
the micro-crystalline matte version are primarily the
result of a heavy glaze application.
The vase shown here was thrown from stoneware and the toothy surface of the
clay may have also contributed
to the formation of the micro-crystalline
matte finish.
The vase has an inlay of the glaze satIron_mashiko_neph_Imerys, which displays a golden frame at the boundary.
The design is created by adhering a mask and then applying the main
glaze. After drying, the mask is removed
and the open area filled in with a
second glaze, using a bulb syringe with a needle applicator.
Image of the micro-crystalline matte version of the glaze iron_Alex_0_Z38
vase is ~ 8 inches high
Clay body is cone 10 BMix
Image of the variegated glossy version of the glaze iron_Alex_0_Z38
inside
outside
bowl ~ 4 inches in diameter
Clay body is cone 10 grolleg porcelain from Tacoma Clay Art Center
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
150 deg F an hour to 250 deg F
400 deg F an hour to 1800 deg F
200 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
Down Fire Profile
300 deg F an hour to 1750 deg F then a 50 minute 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
glaze composition
Empirical Formula iron_Alex_0_Z38 :
K2O 0.09
Na2O 0.42
Li2O 0.15
CaO 0.32
MgO 0.02
Al2O3 0.57
Fe2O3 0.16
SiO2 3.34
P2O5 0.03
molecular percent Silica 65%
Inlay Glaze Composition
Empirical Formula satIron_mashiko_neph_Imerys :
K2O 0.08
Na2O 0.11
Li2O 0.28
CaO 0.51
MgO 0.02
Al2O3 0.61
Fe2O3 0.25
SiO2 4.0
P2O5 0.15
molecular percent Silica 66.7%
Remarks
The mug refered to is the same clay as the bowl, from which I conclude
that the dense crystals of the
micro-crystalline matte version are
primarily the result of a heavy glaze application.
The toothy surface of the stoneware may be a contributor to the crystallization on the vase.