This easy to use gel can be applied to any surface and is virtually invisible! When contact is made it transfers the invisible directly into the skin. The invisible dye we use is either red or yellow in colour. Even if wiped off quickly it is very very tough to remove. Can only be seen under UV/Blacklight. Great in situations where immediate apprehension cannot be made. Can remain on skin for several days even after washing! Tough Stuff!. Wnt to know more? Email us for some 1st hand experiences in the capture of common theives!