a low alkali metal glaze in two firings
Here is a glaze caAlSi_hh_K_PFe which has minimal alkali metals, only that
which will be the result
I show this glaze in a firing with substantial downfire holds, and also in a
firing with no downfire
Firing 1 has three holds in the downfire, starting with a 4 hour hold at 1600
degF, then a 4 hour
Firing 2 achieves cone 10 at 2220 degF, a temperature which is commonly used
for cone 6 firings.
This glaze has been fired with several other patterns of downfire holds.
Changing the ordering of
The bowls are respectively ~4 inches in diameter and ~6 inches in diameter.
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 min at 2310 deg F
300 deg F an hour to 1650 degF with a hold of 4 hours at 1650 degF.
400 deg F an hour to 1900 degF with a hold of 4 hours at 1900 degF.
300 deg F an hour to 1650 degF with a hold of 4 hours at 1650 degF.
150 deg F an hour to 250 deg F
400 deg F an hour to 1850 deg F
120 deg F an hour to 2130 deg F
13 deg F an hour to 2190 deg F / hold 2 hours
13 deg F an hour to 2220 deg F / hold 3 hours
Turn Kiln Off
K2O 0.005
Al2O3 0.47
SiO2 2.77
molecular percent Silica 63.6%
K2O 0.18
Al2O3 0.58
SiO2 3.61
molecular percent Silica 65.9%
The second bowl has a splash of a high rutile decoration glaze beneath the
primary glaze on the
In the first firing, there is a prominent greyed green phase, and the iron
markings are a strong brown.
The texture of the glaze in the second firing is rather different, this is
most easily seen in the manner
Does that second bowl, where the glaze crawled over the rutile decorative
glaze have a curled up
of the impurities present in commonly used ceramic
materials.
holds, yet with a slow upfire.
hold at 1900 degF, and finishing with a 4 hour hold
at 1650 degF. That is, this downfire has an upfire
in the middle.
It achieves this with a glacially slow upfire for the
last 90 degF of the firing. The rate of climb is 13 degF
an hour and, in
addition, there is a two hour hold at 2190 degF and another three hour hold at
2220 degF.
the holds at 1650 degF and 1900 degF greatly changes
the pattern of the dark brown and green markings, and
the prominence of the
iron spots, yet all are recognizably the same glaze. Only replacing downfire
holds with an extremely slow upfire transforms the glaze appreciably.
Image of the glaze caAlSi_hh_K_PFe in Firing 1
Image of the glaze caAlSi_hh_K_PFe in Firing 2
oxidation firing to cone 10 in an electric kiln
Firing profile 1
Up Fire profile cone 10
Down Fire Profile cone 10
Firing profile 2
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 caAlSi_hh_K_PFe:
Na2O 0.005
CaO 0.983
MgO 0.007
Fe2O3 0.11
decoration Glaze:
Empirical Formula hiAlk_Z3P_Z3V_0Mng:
Na2O 0.35
CaO 0.45
MgO 0.02
P2O5 0.07
TiO2 0.21
Remarks
inside of the bowl.
In that second firing, the green is entirely
gone, and the markings are not so sharply edged, rather
blending into each
other.
in which the highlights are fuzzed out,
rather than sharply reflective. In that first firing, the glaze
surface
is smooth and hard, but in the second softly textured and that pot feels
smooth to the fingers.
cat asleep within it?