Firing of silicate ceramics, which are made of clays with high contents of kaolinite, transforms a green body into a ceramic product [1, 2]. The green body exhibits significant changes of its properties resulting from dehydration at low temperatures, phase changes during dehydroxylation and high-temperature reactions, and densification during sintering [3, 4]. All these changes significantly influence mechanical properties of the fired body as well as its other physical properties. To save time and energy, it is desirable to conduct the firing in the shortest time possible without damage to the fired ceramic body. Calculating the safe upper limit of the heating or cooling rate of the large ceramic bodies (e.g. high-voltage insulators) is a complex task that requires knowing five material quantities: mechanical strength (MOR), Young’s modulus
(YM), Poisson’s ratio, thermal conductivity, and coefficient of the linear thermal expansion(CLTE). All of these quantities must have to be known as functions of the actual temperatureat the firing.