A composition and a method for determining changes of a site. The composition includes an aqueous dispersion including at least one binder, at least one substance emitting visible light on UV exposure and optionally a dispersant. The method includes treating the site with a composition, exposing the treated site and/or the untreated areas adjacent thereto to UV light, and determining the deviation of the light intensity of the emitted light of the site Immediately after the treatment with the composition from the light intensity of the emitted light at a later time.