Calcium - Magnesium Balance
Two glazes which differ in the balance of CaO:MgO.
The glaze satIron_ZG_0_Z3J is derived from the glaze satIron_ZG_0_PK_MLi
by replacing some CaO with MgO.
I show a section of the glaze satIron_ZG_0_PK_MLi, from a piece with
a design irrelevant to the present purpose.
bowl is ~ 4 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 2170 deg F with a hold of 1 hour at 2170 deg F
120 deg F an hour to 2250 deg F
60 deg F an hour to 2270 deg F with a hold of 30 minutes at 2270 deg F
60 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 hour hold at 1750 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.12
Al2O3 0.64
SiO2 3.23
molecular percent Silica 62.2%
K2O 0.11
Al2O3 0.64
SiO2 3.21
molecular percent Silica 62.3%
A small amount of MgO in a glaze can substantially change its behavior. The
decrease in CaO also is significant
If thick, the glaze satIron_ZG_0_Z3J has a
dense covering of coppery colored metallic micro-crystals. If thin, as
seen
on the outside of the bowl, this glaze has the appearance of a
metallic luster. Neither of these effects
are visible in the glaze
satIron_ZG_0_PK_MLi.
Image of the glaze satIron_ZG_0_PK_MLi
Image of the glaze satIron_ZG_0_Z3J
inside
outside
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 satIron_ZG_0_PK_MLi :
Na2O 0.69
CaO 0.18
MgO 0.01
Fe2O3 0.22
P2O5 0.10
Empirical Formula satIron_ZG_0_Z3J:
Na2O 0.69
CaO 0.14
MgO 0.06
Fe2O3 0.22
P2O5 0.09
Remarks
as it decreases the fraction of the
Calcium-alumina-silica eutectic in the glaze. An abstruse way of saying
that
CaO is a more powerful flux than MgO.