The invention relates to an aqueous paint composition, particularly a lacquer or a varnish and an aqueous colloidal dispersion of cerium. Said dispersion has a pH of at least 7 and comprises an organic acid with at least three acid functions of which the third pK is at most 10 or a salt of said acid with ammonia or an amine. Said composition has an improved water content and mechanical properties which improve throughout the life thereof or the duration of the presence thereof on the substrate for protection.