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Simultaneous effects of the firing cycle parameters on common ceramic properties of an illitic-chloritic raw clay were evaluated by adopting the response surface methodology. Globally, simultaneous use of higher firing temperatures, shorter soaking times, and rapid heating rates may have a positive effect on the considered properties. In other respects, it is shown that the Doehlert design is a useful tool for assessing the clay ceramic suitability. The results obtained by this model could not be predicted by the empirical diagrams where the grain size distribution and the chemical composition are taken into account.

The firing transformations of a Triassic calcareous clay were investigated, in the range 800 –1075ºC, by using X-ray diffraction and by measuring some ceramic properties (linear shrinkage, density and porosity). It was found that gehlenite and wollastonite are the only neoformed crystalline phases, when anorthite is also expected. The occurrence of these phases is discussed, emphasizing the role of the activity of free silica and calcite concentration. Moreover, new reaction paths for anorthite and wollastonite are envisaged.