Evaluation of glauconite rock color stability during firing

The paper analyses the influence of the firing temperature on the mineralogical composition and color stability of glauconite rock—a potential natural color-changing additive in ceramics. By XRD, Mössbauer spectroscopy and colorimetric analysis it has been established that the tint of glauconite rocksʹ color depends on the amount of iron incorporated into hematite and magnesioferrite. The intensity of red color rises as the amount of iron in hematite increases. The ceramic body becomes darker, when more iron is incorporated into magnesioferrite and the difference between the amount of iron in magnesioferrite and hematite is higher. Firing temperature intervals in which the color of glauconite rocks does not change have been determined. The color of the rock in each interval remains stable but the tint of the ceramic body fired in different temperature ranges varies. Therefore, glauconite rock is suitable for adjustment of the color of easily fusible clay.