More Alumina

Firing profiles

Up Fire profile

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 2300 deg F with a hold of 20 minutes at 2300 deg F

Down Fire Profile

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

Clay body is a grolleg porcelain from Tacoma Clay Art Center.

Both glazes are high in Phosphorus

Empirical Formula glaze satIron_ZT_MashikoLi_1H_MSiAl :

K2O        .01
Na2O        .01
Li2O        .23
CaO        .47
MgO        .28

Al2O3        .51
Fe2O3        .2

SiO2        3.38
P2O5        .14

molecular percent Silica 64%

Empirical Formula glaze satIron_ZT_Mashiko_Z1N_2 :

K2O        .01
Na2O        .01
Li2O        .24
CaO        .47
MgO        .27

Al2O3        .42
Fe2O3        .19

SiO2        3.3
P2O5        0.16

molecular percent Silica 65%

Remarks

The high alumina glaze is mature, the lower alumina glaze is not.

The high alumina glaze is a glossy variegated orange-y glaze, with scattered silvery metallic micro-crystals.
It's surface is smooth.

The low alumina glaze surface has dry volcanic regions intermixed with smoother micro-crystalline sections.
The thin glaze application on the outside of the bowl is a textured gloss glaze with only occasional
rough patches.

The low alumina glaze appears underfired, fully melted only with thin application.

That low alumina glaze is a member of a family of high alkali metal, high phosphorus, lower alumina glazes,
tested together and all declared underfired.

Later, after testing the high alumina glaze satIron_ZT_MashikoLi_1H_MSiAl, which differed primarily in higher alumina,
I question the underfired conclusion.

Perhaps the micro-crystals form in great volume in the low alumina glaze, and float to the surface, thus dominating the glaze.
This glaze is perhaps not underfired, but is instead oversaturated with micro-crystals.