increasing silica
Here are two glazes, a waxy matte iron yellow glaze with orangy speckles, and
a semi-translucent
The first glaze has the crusty look of a micro-crystalline matte with a large
grain size.
The second glaze, ironYellow-PSi differs from the first by an increase in
silica. It has a smoother, nearly
Some close-up images are shown for each glaze, and images of the pot.
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 3 hr hold at 1650 deg F
400 deg F an hour to 1900 deg F then a 3 hr hold at 1900 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
300 deg F an hour to 1700 deg F then a 3 hour hold at 1700 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 3 hr hold at 1650 deg F
400 deg F an hour to 1850 deg F then a 2 hr hold at 1850 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
300 deg F an hour to 1700 deg F then a 3 hour hold at 1700 deg F
K2O 0.07
Al2O3 0.53
SiO2 2.55
molecular percent Silica 61.5%
K2O 0.07
Al2O3 0.52
SiO2 3.06
molecular percent Silica 65.6%
These two glazes were fired in different firings, both firings are 'invert'
down-firings, drop to 1650 degF
These two firings differ in the temperature and length of time of the high
hold that follow the drop to
mottled iron glaze with a multitude of distinct iron
precipitates.
silky surface and is a translucent waxy
matte if thinly applied. With a higher silica:alumina ratio, it
seems more
'melted' that the lower silica glaze from which it was derived.
ironYellow
close ups of glaze ironYellow
ironYellow
bowl is ~3.5 inches in diameter
ironYellow-PSi
close ups of glaze ironYellow-PSi
ironYellow-PSi
bowl is ~3.5 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profile for ironYellow
Up Fire profile cone 10
Down Fire Profile cone 10
Firing profile for ironYellow-PSi
Up Fire profile cone 10
Down Fire Profile cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze compositions
Empirical Formula ironYellow :
Na2O 0.11
CaO 0.81
MgO 0.01
Fe2O3 0.07
Empirical Formula ironYellow-PSi :
Na2O 0.11
CaO 0.81
MgO 0.01
Fe2O3 0.07
Remarks
then up to a higher temperature.
1650 degF. For the glaze ironYellow, the
temperature is 1900 degF and the hold is three hour. For the glaze
ironYellow-PSi, the temperature is 1850 degF and the hold is two hours.
That is the only
difference between the two firings. I do not consider
that difference significant.