Migrating abutting glazes

The interface of 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 tsabar-harris-red; 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 glaze tsabar-harris-red and inlay iron_8_R_C10_13PSi

bowl is 4.5 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 glaze

Empirical Formula tsabar-harris-red :

K2O        0.21
Na2O        0.07
CaO        0.65
MgO        0.01
ZnO        0.06

Al2O3        0.51
Fe2O3        0.02

SiO2        2.88

molecular percent Silica 65%

added:

Copper Carbonate 0.5%
Silicon Carbide 0.5%

Inlay Glaze

Empirical Formula iron_8_R_C10_13PSi :

K2O        0.11
Na2O        0.45
Li2O        0.25
CaO        0.17
MgO        0.02

Al2O3        0.56
Fe2O3        0.28

SiO2        3.12

molecular percent Silica 63%

Remarks

The inlay glaze is a saturated iron glaze high in alkali metals containing CaO; the background glaze is high in Calcium,
contains Zinc and has moderate alkali metals. The background glaze is viscous,
the inlay glaze fluid.

Micro-crystals grow more profusely in the interaction region than in either background or foreground glaze,
and dominate the interaction region.

The bronze part of the interface just above the matrix is covered in crystals, which are only faintly visible
in the photographs. These regions are marked by pits at the corners of the lattice between the abutting crystals,
some of which are 1/4 inch in diameter. These crystals are slightly domed, obscuring the radial needles in the crystals.

The interaction regions is the result of gravity and diffusion. The fluid inlay, applied thickly, flows down the
near vertical wall of the pot. Additionally, there are regions of the design where the iron in the inlay can be seen to have migrated
sideways via diffusion from high concentration in the inlay to low concentration in the matrix.

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