The invention concerns a coating agent for cellulose-bearing substrate surfaces comprising a liquid phase and binding agent, wherein the coating agent includes platelet-shaped pigments and a bonding agent, wherein the platelet-shaped pigments are corrosion-resistant and impermeable to UV light and wherein the bonding agent produces a bond between pigment, binding agent and the cellulose-bearing substrate surface. The invention further concerns the use of the coating agent according to the invention as well as coated cellulose-bearing substrate surfaces.