abstract |
Container caps or containers having a varnish outer coating, or other resinous outer surface, are coded by marking indicia thereon with a fluorescent ink made of a fluorescent brightening agent in an organic solvent but having no resinous vehicle. The solvent softens the varnish and the fluorescent brightening agent penetrates into the varnish layer to remain therein after the solvent is dried off and is brought to view when desired by exposure to ultraviolet light. |