The lapping and polishing processes that provide ceramic tiles with the proper aesthetic features, both involve the removal of a very thin layer of glaze that is on the very external part of the tile.Even if the amount of removed material is very small, these processes may bring out to the surface all that micro-porosity that are inside the glaze.Since they are no more protected and sealed, the pores remain exposed chemical and dirt attack.How do the protective treatments work? What are the chemical mechanisms and what kind of benefit do they promote?