In the current study, nano- and microparticles were used as the
optimum candidates to fill the surface pores of porcelain stoneware
substrates. The use of nano-sized zirconia to produce hard
ceramic materials was previously tested leading to satisfactory
results with respect to mechanical properties. However, the treatment
procedure was unsustainable since two firing steps were
needed. Moreover, the stain resistance issue was not taken into
account.