Reactions between abutting glazes

The interaction between two adjacent glazes.

Several closeups of the interaction region of the two glazes are shown and, for context, a picture of the pot.

The background glaze is satIron_ZG_1O_1Q_1PIron, the foreground design is glazed with iron_8_R_C10_13PSi.

The design is created by adhering a mask and then applying the main glaze. After drying, the entire pot is coated in wax,
then the mask is removed and the open area filled in with a second glaze.

Close up Images of the interaction region

full view

Image of the piece

full view

bowl with glaze satIron_ZG_1O_1Q_1PIron and inlay iron_8_R_C10_13PSi

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 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.

glaze compositions

Background glaze

Empirical Formula satIron_ZG_1O_1Q_1PIron :

K2O        .24
Na2O        .22
Li2O        .24
CaO        .16
MgO        .14

Al2O3        .46
Fe2O3        .25

SiO2        3.13
P2O5        .04

molecular percent Silica 64%

Inlay Glaze

iron_8_R_C10_13PSi :

K2O        .11
Na2O        .45
Li2O        .25
CaO        .17
MgO        .02

Al2O3        .56
Fe2O3        .28

SiO2        3.12

molecular percent Silica 63%

Remarks

The interaction region dominates the design, occasionally leaving nothing untouched of the design glaze inlay.

The design glaze, iron_8_R_C10_13PSi, differs from the background glaze satIron_ZG_1O_1Q_1PIron in that
it contains no P2O5 and only a trace of MgO.

Otherwise, these two glazes seem to be saturated iron glazes with similar compositions. However, they are
not as similar as they might appear - else why the strong reaction of the decoration glaze with the MgO and P2O5 diffusing
across the boundary between it and the background glaze?

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