Which of the following methods is used for demonstrating old washed up blood-stains -
Infrared photography
Luminol spray
Ultraviolet light
Magnifying lens
Luminol (3-aminophthalhydrazide) spray is most common blood reagent used for visualizing/demonstrating weak/ faint blood stains i.e old washed up or cleaned up stains and blood stains in areas difficult to see such as outdoor vegetations etc.