crossing lines

Here I show two pieces with micro-crystals on a glossy background: One has a transparent glossy pale amber background
with pale golden acicular crystals, the other a deap brown background with the micro-crystals merging into a nearly opaque curtain.

A line is crossed. These two dissimilar appearing glazes have nearly equal alumina and silica, and only small differences
in the other oxides in their empirical formulae except that the first has slightly higher Lithium, and correspondingly
lower Calcium. These glazes are in distinct glaze families. The composition of the phases in these two glazes are different.

The first glaze is a full gloss in which small crystals form; the second is a mixture of a dark textured gloss glaze
and a microcrystalline matte glaze, in which a few scattered clusters of larger crystals have formed. The second glaze contains
none of the acicular crystals with needles extending radially from center to edge, which are found so prominently
in the first glaze.

The design, which is not addressed in this analysis, is created by adhering a mask and then applying
the main glaze. After drying, the mask is removed and the open area filled in with a second glaze.

Image of the pieces

full view

vase with glaze satIron_Alex_Puah and inlay satIron_ZG_Ip7_5

vase is ~ 11 inches high.

full view

bowl with glaze iron_Alex_Puah_14 and inlay hankPaper_Z1R_2C_1

Bowl is ~7 inches in diameter.

oxidation firing to cone 10 in an electric kiln

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 2310 deg F with a hold of 20 minutes at 2310 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.

glaze compositions

Background glazes

Empirical Formula satIron_Alex_Puah :

K2O        0.08
Na2O        0.33
Li2O        0.18
CaO        0.23
MgO        0.18

Al2O3        0.65
Fe2O3        0.07

SiO2        3.05
P2O5        0.03

molecular percent Silica 63.5%

Empirical Formula satIron_Alex_Puah_14 :

K2O        0.07
Na2O        0.33
Li2O        0.14
CaO        0.30
MgO        0.16

Al2O3        0.64
Fe2O3        0.07

SiO2        3.0
P2O5        0.04

molecular percent Silica 62.7%

Inlay Glazes

satIron_ZG_Ip7_5 :

K2O        0.07
Na2O        0.44
Li2O        0.20
CaO        0.12
MgO        0.17

Al2O3        0.71
Fe2O3        0.1

SiO2        3.13
P2O5        0.04

molecular percent Silica 62.9%

Empirical Formula hankPaper_Z1R_2C_1 :

K2O        0.12
Na2O        0.12
Li2O        0.05
CaO        0.14
MgO        0.02
BaO        0.31
SrO        0.24

Al2O3        0.42

SiO2        2.7
TiO2        0.14

molecular percent Silica 63%

Added:

1% Cobalt Carbonate .67% Copper Carbonate

Remarks

In the computed empirical formulas, the primary difference is that the first glaze satIron_Alex_Puah has
higher akali metals and lower CaO. The difference in appearance between these two glazes seems large
for the shift in composition.

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