Risk Reactor's IFPAP Series invisible porous invisible is specially made for porous substrates such as paper, cardboard, cloth, etc. Common uses are document protection and authentication, ownership, invisible markings, dual-purpose documents, arts and crafts, document tracking, product control, and quality control of porous materials. These inks do not leave a film but can cause a visible mark depending on the type of material it is being applied. Always check a small amount to make sure you get the desired result. Appears clear except under a Black Light. Used to Mark Paper or Porous Surfaces. Risk Reactor's Porous Surface Marking Ink dries very Fast. Used Primarily to Invisibly Mark Paper Products such as Important Documents, Cardboard, Textiles, Money, Clothes, etc.