Iron is among the most powerful of fluxes in reduction firing. This is normally a glossy glaze, but the kiln was slow-cooled, resulting in total crystallization of the surface. The crystals are larger and layered at the neck. Their presence, as a thin layer on top, has completely matted the rest of the surface. Enough glaze ran downward off the piece that the vase was left sitting in a pool of molten glass.
Troubles |
Glaze is excessively runny on firing
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Glossary |
Crystallization
Ceramic glazes form crystals on cooling if the chemistry is right and the rate of cool is slow enough to permit molecular movement to the preferred orientation. |