Alumina and Texture
Here we saw
The Effect of increased alumina on the color of a glaze containing
lithium.
Those glazes, as most of my high alkali metal saturated iron glaze contain
lithium. It had been suggested that the lithium
The following two glazes differ only in alumina.
In these tests, low alumina resulted in an orange/dark orange glaze. Unlike
the previous low-alumina glaze which contained lithium,
The current test with increased alumina resulted in a full gloss glaze with a
dusting of gold colored metallic crystals.
The low alumina glaze
This glaze is a textured gloss, with a two tone orange pattern. In the bottom
of the bowl with a thick glaze application,
The high alumina glaze
This glaze is a full gloss light orange with a dusting of metallic gold.
It has a lighter less forceful color than the low alumina glaze above.
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 2300 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 .1
Al2O3 .55
SiO2 3.76
molecular percent Silica 66%
K2O .11
Al2O3 .62
SiO2 3.77
molecular percent Silica 65%
In this prior test, low alumina resulted in a dark glaze with
speckles of very dark red, orange and black;
higher alumina resulted in a
lighter, yellow tan glaze.
was responsible for the
differences seen. So I experimented with increasing alumina in a glaze with
no lithium.
Because the alkali metals:alumina ratio is limited by the
lack of lithium, these glazes contain boron.
it does not have the
strong color variation.
In this case, the crystals appear
more dominant than in the increased alumina glaze that contained lithium.
Glaze hiAlk_Z1W
bubbles are frozen in an
unpopped state, making visible the cause of the color variation as a lighter
tone
where a blister had popped.
bowl is ~3.5 inches in diameter
Glaze hiAlk_Z1W_PAl
bowl is ~3.5 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 hiAlk_Z1W
Na2O .64
CaO .23
MgO .03
B2O3 .11
Fe2O3 .26
P2O5 .06
Empirical Formula glaze hiAlk_Z1W_PAl :
Na2O .62
CaO .24
MgO .03
B2O3 .11
Fe2O3 .26
P2O5 .06