Abutting Glazes Mixed

I call a pair of glazes, applied side by side, with no overlay, abutting glazes

Here I show the contrast between a pair of abutting glazes, and the same two glazes mixed together.
That mixture of equal parts of the two glazes is also described as the midpoint of a line blend of the two glazes.

I do this for two distinct pairs of abutting glazes:

The interface of iron_8R_C10_13PSi and and satIron_ZG_1O_1MFe

The interface of nepheline_Z1A_2MAlk and and satIron_ZG_1O_1MFe

For reference, images of the interface of each pair, together with the empirical formula for each glaze of the pair are given below:

iron_8R_C10_13PSi and and satIron_ZG_1O_1MFe

nepheline_Z1A_2MAlk and and satIron_ZG_1O_1MFe

The Pair iron_8_R_C10_13PSi and satIron_ZG_1O_1MFe

An image of the interface of the abutting glazes, followed by an image of the glaze, iron_8_R_Plus_satIron_ZG,
the mixture of the two.

full view

glaze iron_8_R_Plus_satIron_ZG

The Pair nepheline_Z1A_2MAlk and satIron_ZG_1O_1MFe

An image of the interface of the abutting glaze, followed by an image of the glaze, nepheline_Z1A_Plus_satIron_ZG,
the mixture of the two.

full view

glaze nepheline_Z1A_Plus_satIron_ZG

all pieces shown are small bowls ~4 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 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.

glaze compositions

Empirical Formula iron_8_R_Plus_satIron_ZG :

K2O        .18
Na2O        .34
Li2O        .24
CaO        .17
MgO        .07

Al2O3        .52
Fe2O3        .18

SiO2        3.25
P2O5        0.04

molecular percent Silica 65%

Empirical Formula nepheline_Z1A_Plus_satIron_ZG :

K2O        .16
Na2O        .31
Li2O        .21
CaO        .13
MgO        .19

Al2O3        .59
Fe2O3        .14

SiO2        3.45
P2O5        .03

molecular percent Silica 66%

Remarks

The chemical reactions which occur in a ceramic glaze during firing are limited by temperature and proximity of the required reactants.

The movement of particles across the boundary between abutting glazes rearanges the possibilities for chemical reactions
by altering the relative positions of reactants. This promoting some reactions while blocking others.

This rearangement of reactants in the interfacial region between abutting glazes stands in contrast to the more
homogeneous environment found in the mixture of the two glazes. This dance of the components permits more varied
chemical reaction in and near the interface than is possible in the mixed glaze.

This variation in local chemistry in the interface between abutting glazes produced ephemeral effects not seen in the mixture:
the mixture of the two glazes has a more homogenized look as a result of a less varied chemisry. It is
more likely to display a single dominant a single dominant effect.

iron_8_R_Plus_satIron_ZG, the mixture of the abutting glazes iron_8_R_C10_13PSi and satIron_ZG_1O_1Q_1MFe,
lacks the clusters of metallic crystals and the varied purple black matrix seen in the interface of the two glazes.
It is a more uniform mottled brown-black with orange spots and a dusting of metallic sparkle.

nepheline_Z1A_Plus_satIron_ZG, the mixture of the abutting glazes nepheline_Z1A_2MAlk, and satIron_ZG_1O_1Q_1MFe,
is missing the bright red spots and the maroon crystals seen in the interface. It is a near uniform glossy mustard colored glaze,
a color much greyed and subdued compared to the bright yellow seen in the interface.

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