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The lower bars are cone 6 and 8 oxidation. The iron converts to a flux in reduction (top bar) and by cone 10 it is overfired enough that it is expanding.
| Glossary |
Reduction Firing
A method of firing stoneware where the kiln air intakes and burners are set to restrict or eliminate oxygen in the kiln such that metallic oxides convert to their reduced metallic state. |
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