The whitening of calcareous ceramics was
studied in Mössbauer spectroscopy and X-Rays diffraction. This
phenomenon is similar to that which occurs in firing calcareous clays
without chloride, but it appears at lower temperature : NaCl accelerates
the formation of calcium aluminosilicates susceptible of Fe3+
-trapping. The alkali metals are lost, during firing, in the form of
chlorides. Their loss percentage increases from Li to Rb ; it augments
also in function of CaCO3 and NaCl proportions.