The influence of mineralogical composition on the colour of clay body

By using methods of Mössbauer spectroscopy, X-ray diffraction and colorimetrics analysis, the dependence of the colour of a ceramic body on its mineralogical composition was determined. In order to achieve this objective, the mineralogical composition and colour parameters of the Girininkai deposit (Lithuania) easily fusible clay and its mixture with the glauconite rock during firing at 600, 800, 1000, and 1025 °C were investigated in detail. By changing firing temperature from 600 to 1025 °C and duration of isothermal exposure from 0.5 to 4 h the amount of iron in hematite increases 5 times, whereas the amount of Fe3+ incorporated into the crystal lattice of other compounds diminishes 3–4 times if compared with natural clay. For this reason, the value of red colour coordinate increases from 18.44 to 23.65 NBS units and the ceramic body darkens and becomes redish brown. The colour can be intensified even more by adding to the forming mass finely ground glauconite.