Resistance to chemicals

RESISTANCE TO CHEMICALS EN ISO 10545-13
Resistance to chemicals is the capacity of the surface at room temperature to tolerate contact with chemicals (domestic products, staining chemicals, pool additives, acids and solvents) without alteration in its appearance.
Unglazed tiles are divided into categories starting with U and for glazed tiles the category starts with G.

Category A means they was no visible effect and for C there is a visible effect on the sides of the tile and the surface.