Luminol: The Crime-Scene Glow

This simulation recreates the forensic luminol test used to reveal trace blood evidence at a crime scene. A flat surface hides a random trace pattern — a footprint, a handprint or a wipe smear — left behind by residual iron catalyst that is completely invisible to the eye. Spray the luminol/hydrogen-peroxide solution across the surface with click-and-drag: everywhere the solution contacts the hidden iron-catalyzed trace, chemiluminescent oxidation lights up a real blue glow with no external light source, while the rest of the sprayed surface stays dark. Luminol and oxidizer concentration control how bright the reaction glows, and the decay-time slider controls how long the excited-state emission persists before the reagents are consumed and the glow fades — reset to wet a fresh surface with a newly hidden trace.