Fe2O3 (Iron Oxide, Ferric Oxide)

Notas

Ferric oxide (Fe2O3), naturally occurring as hematite, serves as the primary ceramic colorant and a versatile modifier of glaze and clay body chemistry. Chemically amphoteric, it exhibits a dual role depending on the kiln atmosphere: in oxidation, it functions primarily as a refractory stabilizer similar to alumina, which increases melt viscosity and prevents running; in reduction, it transforms into FeO, acting as a potent flux that significantly increases glass fluidity. Proper oxidation between 700-900°C is essential to maintain its ferric state, as premature reduction can lead to irreversible fluxing. Color development is highly sensitive to the base glaze chemistry and kiln conditions, ranging from ambers and yellows at low percentages to deep browns at higher concentrations. At levels approaching 20%, iron often induces matteness. Due to its limited solubility in many silicate melts, iron frequently precipitates during cooling to form crystals, a characteristic utilized in aventurine glazes. When added in quantities exceeding 1-2%, it typically contributes to a reduction in glaze crazing. Fe2O3 interacts complexly with other oxides, such as rutile and titanium, which promote variegation, or zinc, which may result in undesirable color shifts. In clay bodies, it acts as a primary colorant, with concentration and firing temperature dictating the shift from oranges and light reds to dark browns.