Replacing Calcium with Magnesium
Two glazes differ only in the balance of calcium oxide to magnesium oxide.
The glaze satIron_ZG_0_Z3K was derived from the glaze satIron_ZG_0_Z3J by
replacing some CaO with MgO.
Where thickly applied, the glaze satIron_ZG_0_Z3J has orange and even coppery
colored micro crystals on a chocolate
By contrast, even where thickly applied, satIron_ZG_0_Z3K shows a smooth,
though pitted, lusterous surface
Both pots were glazed thickly on the inside, and thinly on the outside. It is
interesting that the thinly glazed
This is a small shift in calcium oxide to magnesium oxide, yet it changes the
character of the glaze.
bowl is ~ 4 inches in diameter.
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 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 1800 deg F then a 2 hr hold at 1800 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
50 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 0.11
Al2O3 0.64
SiO2 3.21
molecular percent Silica 62.3%
K2O 0.11
Al2O3 0.63
SiO2 3.2
molecular percent Silica 62.3%
colored background. Where even thicker,
in the bottom of the bowl, we see sharply edged nearly dendritic crystal
clusters. The glaze is notably bumpy as seen by the reflections.
with a combination of greenish brown and
yellow rounded fuzzy crystal clusters.
outsides look similar, compared to
the difference seen in the micro-crystals formed on the insides where the
glaze was thickly applied.
The color shifts from an orangy cast to a
mustard, and the micro-crystals change shape as well.
Image of the glaze satIron_ZG_0_Z3J with higher Calcium
Image of the glaze satIron_ZG_0_Z3K with higher Magnesium
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_Z3J:
Na2O 0.69
CaO 0.14
MgO 0.06
Fe2O3 0.21
P2O5 0.09
Empirical Formula satIron_ZG_0_Z3K :
Na2O 0.68
CaO 0.10
MgO 0.10
Fe2O3 0.21
P2O5 0.08