Hydro-Print (Small Particle Reagent - SPR) is specifically formulated for developing latent prints on wet surfaces such as automobiles, windows, and other nonporous surfaces found outdoors. Simply mist Hydro-Print (white for dark surfaces, black for light surfaces) on the wet/damp surface where you suspect prints may be found, then spray rinse water on the developed prints to remove excess Hydro-Print. The small particles that are used in Hydro-Print adhere to the oils found in latent prints. The developed print can be photographed and lifted. Hydro-Print can also be used for latent print development on greasy windows, galvanized or oxidized surfaces, and waxy or plastic surfaces such as polyethylene or polystyrene. Note: Most effective if used within six months of manufactured date. Keep in a cool, dark place.