This International Standard specifies a spectral photometric method with 1,10-phenanthroline for the quantitative determination of Fe2+ and Fe3+ in oxidic raw and basic materials for ceramics, glass and glazes, e.g. feldspar, kaolinites, clay, limestone, quartz refractory materials. This International Standard could be extended to other aluminosilicate materials, providing that uncertainty data is produced to support it. However, there might be problems in the decomposition of high-purity alumina and chrome ore samples. The method is not suitable for reduced materials, such as silicon carbide, graphite-magnesia, etc.