A mysterious yellow band
This is a further exploration of a firing which has a slow up-fire in
addition to having the usual
The matrix glaze, hiAlk_satIron_Z4L_0, is a high silica
iron-titanium-phosphorus glaze,
That bright yellow band framing the inlay is seen in the last close-up image
to be bounded on both
Perhaps that yellow is an iron yellow, and the sharpness of the boundary is
the result of the narrow
Perhaps, as with the many colors in the background glaze, these distinct bands
of color are various iron
I'm curious about the chemistry that caused these sharply demarcated bands of
distinct colors about the inlay.
The matrix (i.e., background) glaze and inlay glaze overlap minimally before
firing. The width of the
The design is created by adhering a mask and then applying the main
glaze. After drying,
The close-up images were heavily edited to enhance detail. The colors of the
full image of the bowl
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 then a 90 min hold at 2220 deg F
90 deg F an hour to 2320 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 hr hold at 1650 deg F
K2O 0.12
Al2O3 0.62
SiO2 3.17
molecular percent Silica 62.5%
K2O 0.07
Al2O3 0.33
SiO2 2.47
molecular percent Silica 65%
Added:
1.5% Nickel Oxide
This firing features a 'rounded at the top' firing profile; with a hold of an
hour and a half at 100 degreesF
holds on the way down.
variegated with multiple competing iron
bearing micro-crystals. The inlay glaze, cooper_404_1Na_PMZn,
which I have
characterized as a calico glaze; is a zinc-barium confection with almost no
calcium,
yet as high in silica as the matrix glaze. It has its own crystals.
The many distinct oxides these two
compositions provide for the
occurrence of a distinctive sharply demarcated yellow band in the
interaction
region.
inside and outside by a narrow brown band.
Additionally, sharply pointed needle crystals are seen within
that yellow
band. Careful inspection even shows a chartreuse band between that yellow and
the brown edging
bounding the inside border of the background.
window of concentration in which iron can be
yellow. That would be fully consistent with the difficulty
of producing an
iron yellow glaze.
bearing micro-crystalline clusters, in various sizes
and compositions.
original inlay varied from an eighth of
an inch to three quarters of an inch.
the mask is removed and the open area filled in with a
second glaze, using a bulb syringe
with a needle applicator.
are as they appear in bright light.
Close up Images of the interaction region
Image of the piece
bowl with glaze hiAlk_satIron_Z4L_0 and inlay cooper_404_1Na_PMZn
bowl is ~6 inches in diameter
oxidation firing to a hot cone 10 in an electric kiln
Firing profiles
Up Fire profile hot cone 10
Down Fire Profile hot cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze composition
Empirical Formula hiAlk_satIron_Z4L_0 :
Na2O 0.54
CaO 0.32
MgO 0.02
Fe2O3 0.10
P2O5 0.07
TiO2 0.11
Inlay Glaze:
Empirical Formula cooper_404_1Na_PMZn
Na2O 0.27
CaO 0.04
MgO 0.01
BaO 0.22
ZnO 0.39
Remarks
below top temperature, and a slow climb
from there to the top temperature.