Magnesium vs. Calcium
A prominent opaque second phase in a clear glaze nearly dissapears
with increased Magnesium.
The second glaze has more Magnesium and less Calcium than the first
glaze.
The glaze with high Calcium, low Magnesium.
A transparent pale white glaze with prominent opaque white inclusions.
glaze with lower CaO, and higher MgO
Glaze is a pale purple-y off white with flecks of the white crystals so
prominent in alkTi_ZQ_2.
150 deg F an hour to 250 deg F
400 deg F an hour to 2050 deg F
120 deg F an hour to 2295 deg F with a hold of 30 minutes at 2295 def G
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 .13
Al2O3 .51
SiO2 4.3
molecular percent Silica 72%
K2O .13
Al2O3 .51
SiO2 4.3
molecular percent Silica 72%
The effect on the appearance of the glaze of replacing some CaO with MgO is a
surprise. The second glaze with higher MgO is less viscous,
The crazing of the second glaze is the result of the low CaO. Reducing
the alkali metals and increasing the CaO might remedy this defect,
The low MgO higher CaO glaze, alkTi_ZQ_2, has a thick roll of glaze at its
foot. This is an indication of a more viscous glaze.
Glaze alkTi_ZQ_2
bowl is ~4 inches in diameter
Glaze alkTi_ZQ_3
bowl is ~4 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 glaze alkTi_ZQ_2 :
Na2O .23
Li2O .26
CaO .31
MgO .07
TiO2 0.2
Empirical Formula Glaze alkTi_ZQ_3
Na2O .23
LI2O .26
CaO .06
MgO .32
TiO2 .2
Remarks
not the expected
result from either increasing MgO, nor decreasing CaO.
while
retaining a similar look and feel of the glaze.