Alkali vs Calcium
Two glazes which differ in the balance of alkali metals and alkaline earths.
The first glaze faux-tsabar-ru-Z2U-0 is higher in alkali metals, the second in
alkaline earths.
The higher alkali metal glaze:
Inside of bowl:
Outside of bowl:
The higher calcia glaze:
Inside of bowl:
Outside of bowl:
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 half hour 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
K2O 0.19
Al2O3 0.54
SiO2 2.84
molecular percent Silica 65%
Added:
0.5% Copper Carbonate
0.5% silicon carbide for local reduction
K2O 0.15
Al2O3 0.55
SiO2 2.8
molecular percent Silica 64%
added:
0.5% Copper Carbonate
0.5% silicon carbide for local reduction
Both of these glazes are multi-phase assemblages, containing both a full gloss
phase and a waxy matte phase.
In the high alkali metal glaze, faux-tsabar-ru-Z2U-0, the full gloss phase
dominates, and is purple.
In the high calcia glaze, faux-tsabar-ru-Z2U-1, the waxy matte phase
dominates. Additionally, in this glaze,
If applied thickly, the high calcia glaze, faux-tsabar-ru-Z2U-1, has interesting
marking, yet is crazed.
Some potassium oxide and sodium oxide in the first glaze is
replaced with calcium oxide
to get the second glaze.
The glazes
faux-tsabar-ru-Z2U-0
bowl is ~3 inches in diameter
glaze faux-tsabar-ru-Z2U-1
bowl ~3 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula faux-tsabar-ru-Z2U-0 :
Na2O 0.23
CaO 0.45
MgO 0.13
Empirical Formula faux-tsabar-ru-Z2U-1 :
Na2O 0.13
CaO 0.59
MgO 0.13
Remarks
the glossy phase is mixed aqua
and pink, showing it to have a different composition that the glassy phase
in
the high alkali metal glaze.