Ferric oxide (Fe2O3).
Iron oxide is present in most ceramic raw materials. It is for this reason that it is the only colouring oxide included in the Glaze Calculator. It reacts differently depending on the atmosphere in which it is fired. In a reduction atmosphere it turns to Ferrous oxide (FeO) and becomes a strong flux. As a basic oxide FeO is included in the unity of a unity formula.
Common raw materials are Red Iron oxide, Black Iron oxide and Yellow Ochre.
Ferric oxide is an amphoteric oxide.
Ferrous oxide is a basic oxide.