Several studies have been carried out to establish a relationship
between the surface microstructure and stain resistance. The
roughness and the total amount, size, and morphology of surface
pores have been proved to be the most influent variables [7–9].
Porosity results from a number of complex phenomena simultaneously
occurring during sintering. A liquid phase forms at about
1100–1150 C and it diffuses through the interconnected pores filling
them