micro-crystals in a saturated iron glaze

With lower alkali metals, less time is required in the downfire holds for the development of substantial
surface micro-crystals.

This glaze wisskirchen-crystals-PAl-MAlk has the same silica and alumina, and lower alkali metals
than the glaze shown here.

We show wisskirchen-crystals-PAl-MAlk in two firings.

In the first firing, with no downfire holds, we see a glossy mottled brown black glaze with a light dusting of
white particles. By contrast, with holds in the downfire, a variegated mixture of yellow, orange
and brown micro-crystals are seen, together with a spattering of glossy black particles. Only where the
glaze was applied overly thick in the base of the bowl do we seen a small puddle of gloss glaze.

The lower alkali metals of this glaze compared to that in the above note allow substantial micro-crystalline
crystal growth with less time in the downfire holds.

Image of the glaze wisskirchen-crystals-PAl-MAlk in Firing 1

full view

Image of the glaze wisskirchen-crystals-PAl-MAlk in Firing 2

full view

The bowls are ~4 inches in diameter.

oxidation firing to cone 10 in an electric kiln

Firing profile 1

Up Fire profile cone 10

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 min at 2310 deg F

Down Fire Profile cone 10

Turn Kiln Off

Firing profile 2

Up Fire profile cone 10

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 min at 2310 deg F

Down Fire Profile cone 10

300 deg F an hour to 1850 degF with a hold of 2 hours at 1850 degF
300 deg F an hour to 1750 degF with a hold of 1 hours at 1750 degF
300 deg F an hour to 1700 degF with a hold of 3 hours at 1700 degF
25 deg F an hour to 1650 degF with a hold of 1 hours at 1650 degF

Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.

glaze composition

Empirical Formula wisskirchen-crystals-PAl-MAlk :

K2O        0.08
Na2O       0.18
CaO        0.69
MgO        0.05

Al2O3      0.55
Fe2O3      0.35

SiO2       3.48
TiO2       0.04

molecular percent Silica 64.2%

Remarks

This is a high iron glaze, resulting in higher fluidity than one might expect given its relatively
low alkali metals:alumina ratio of 0.48

Carol's Home Page