cobalt colors in simplified firings
The glaze, zincSr_Z3W_0 in many flavors is
The appearance of this glazes is transformed by modifications of the
As a first attempt to prize apart the many variables, I fired this glaze in
four distinct firings, one with
All four firings have the same up-fire protocol.
Firing 1:
No holds - a baseline firing.
Firing 2:
In the down-fire, there is one four hour hold at 1900 degF.
Firing 3:
In the down-fire, there is one four hour hold at 1650 degF.
Firing 4:
In the down-fire, there is one four hour hold at 1750 degF.
The design is a slip trailed contrast glaze applied first to the bisque,
subsequently followed
The bowls are 5 to 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 minutes at 2310 deg F
Turn off kiln.
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 minutes at 2310 deg F
300 deg F an hour to 1900 deg F then a 4 hr hold at 1900 deg F
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 minutes at 2310 deg F
300 deg F an hour to 1650 deg F then a 4 hr hold at 1650 deg F
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 minutes at 2310 deg F
300 deg F an hour to 1750 deg F then a 4 hr hold at 1750 deg F
K2O 0.19
Al2O3 0.53
SiO2 3.08
molecular percent Silica 66.8%
Added:
2.5% Cobalt Carbonate
One of hiAlk_Z3P_Z3V_0Mng or hiAlk_Z3P_Z3V_0Munge
K2O 0.18
Al2O3 0.58
SiO2 3.61
molecular percent Silica 65.9%
K2O 0.17
Al2O3 0.61
SiO2 3.50
molecular percent Silica 65.2%
I note that the firing with one 4 hour hold at 1750 degF is most like what
had been seen in former firings,
shown here .
down-fire holds in the firing. Mixed pinks, lavenders, purples and blues, and
even some peach colors
are seen. The micro-crystalline clusters are
large and small, intermixed or sharply color segregated.
How does the
order and duration of the holds create the many distinct patterns seen above?
no holds, the others with only one
down-hold. The down-fire holds were all of the same four-hour
duration, but
occured at different temperatures.
by application of the matrix glaze.
Image of the glaze zincSr_Z3W_0 in Firing 1
Image of the glaze zincSr_Z3W_0 in Firing 2
Image of the glaze zincSr_Z3W_0 in Firing 3
Image of the glaze zincSr_Z3W_0 in Firing 4
oxidation firing to cone 10 in an electric kiln
Firing profiles
Firing 1 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Firing 2 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Firing 3 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Firing 4 profile
Up Fire profile cone 10
Down Fire Profile cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze composition
Empirical Formula zincSr_Z3W_0:
Na2O 0.28
CaO 0.02
MgO 0.19
SrO 0.14
ZnO 0.18
decoration Glaze:
Empirical Formula hiAlk_Z3P_Z3V_0Mng:
Na2O 0.35
CaO 0.45
MgO 0.02
P2O5 0.07
TiO2 0.21
Empirical Formula hiAlk_Z3P_Z3V_0Munge:
Na2O 0.42
CaO 0.31
MgO 0.10
P2O5 0.07
TiO2 0.18
Remarks
yet it doesn't show any of the striking
variation seen in prior firings.