Our easy to use non-drying grease can be applied to any surface indoors and outdoors and is completely invisible to the naked eye. The grease comes in Blue or Green colour options. The grease will not cure or dry out and is ideal for catching criminals "after" the act. The moment that skin or clothing makes contact an invisible colour mark is transferred. Because of our unique grease formula, the mark becomes very difficult to remove even through aggressive washing. Colour mark can only be seen using a 365nm blacklight. Great in situations where immediate apprehension cannot be made. Will remain on the skin or textile for many days even after washing! Tough Stuff!