Fig. 10shows the microstructure obtained at heating rates of 2 and 251C min−1, both for a 360 min holding time. The formation of crystals along the whole sample and certain isolated and rounded pores are visible. The boundary of the frits showed more distinctness for the material obtained at 21C min−1 due to the longer holding time during the crystallization of wollastonite. This visual effect was observed macroscopically and represents an esthetic effect similar to grains dispersed in a translucent matrix in marble. The same effect can be observed for samples heat treated at 925 and 11001C, Fig. 8-e and -g. In the case of the 251C min−1 heating rate, as well as the 101C min−1 rate (Fig. 8-f), the lack of distinctness in the boundaries of the frits interfered with the formation of the desired esthetic effect.