You are probably familiar with forensic luminol from the many references to it on TV crime shows. It is sprayed on areas where blood is believed to be present. The luminol reacts with the iron in blood hemoglobin and glows a bluish purple when the lights are turned out. It will actually react to any iron present on a surface where it is sprayed. (Ref 1) You can buy luminol, but you can also make it on your own.
Mix the luminol powder and washing soda together as a dry mixture in a bowl.
Stir in the distilled water a little at a time.
Add the hydrogen peroxide to the mixture in the bowl a little at a time. Stir the solution thoroughly.
Pour the solution into a spray bottle.
Spray the luminol on a bloodstained cloth and turn out the lights. The cloth should glow a bluish-purple.