This is that hard to find UV Blacklight Reactive Invisible Ink for hand marking, body art, document marking, or other unique security applications. Only visible under black light. Ink is water proof and very difficult to remove. Best viewed in dark or shaded area. Opticz Blacklight Reactive Invisible all purpose inks are suitable for use on skinor work well on pourous materials. This ink is invisible/colorless and will glow bright blue under UV blacklight. Can be used on: aluminum, cardboard, ABS, acrylic, rubber, cellulose, acetate, formica, nylon, polystyrene, Polyethylene and most other materials and porous surfaces. Each high quality solid aluminum marker is filled with 15ml of our special blend UV ink. Ink is alcohol solvent based so a little goes a very long way! Ink is formulated to fluoresce brightly under long wave ultraviolet light only. They do NOT glow in the dark! Fast drying and non-transferable. Ideal for applying onto an already printed surface. Avoid eye contact and excessive inhalation. Do not ingest. KEEP OUT OF THE REACH OF CHILDREN.