This all-purpose Pen may be used for marking just about any porous material with an invisible, permanent, highly fluorescent tag for identification and tracing. Permanently marks paper, cardboard, cloth, wood and other porous materials. Markings may be removed from glass, plastics, metals and other non-porous materials. Markings fluoresce a brilliant blue/white when exposed to longwave (UV) or shortwave (UV) radiation. Perfect for marking location of highly movable items.