Which of the following methods is used for demonstrating old washed up blood-stains -: (A) Infrared photography, (B) Luminol spray, (C) Ultraviolet light, (D) Magnifying lens
Answer is B. 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.