We’ve all seen the dramatic moment in detective shows when the investigators walk into a seemingly immaculate crime scene, flip the lights off, and see the eerie blue glow as the blood spatter lights the room up like an EDM club.
The chemical is called Luminol, and it’s used by forensic investigators to detect trace amounts of blood by reacting with the iron in hemoglobin to create the chemiluminescent effect.
For the latest installment of Investigation Discovery’s video series DIY CSI, I road-tested the blood reagent in the studio.
In 1928, German chemist H. O. Albrecht found that blood, among other substances, enhanced the luminescence of Luminol in an alkaline solution of hydrogen peroxide.
Today, there are many different varieties available: Some are meant as teaching tools that merely react with the blood, while others are professional grade and are meant to preserve DNA as well.
I bought a big bottle on Amazon for around $50. It consisted of Luminol powder, which is white to pale yellow in color, with a hydrogen peroxide solution in a spray bottle. As instructed, I mixed the powder in the bottle, put the spray top on, shook it up, and voilà – I’m ready to meet my first victim.
In our demonstration, I used a stuffed bunny rabbit and a tube of synthetic blood, which can also be purchased online. (Note: It’s the type that contains iron and is specially made for testing with Luminol; the stuff you pick up in Rite Aid in the Halloween clearance aisle won’t work!) It is brownish in color, just like real blood — but, unlike real blood, I don’t have to slice into my skin in order to do the demonstration.
After applying the faux blood, I turn the lights out, and our Easter bunny shines.
I spray a lot of Luminol to demonstrate the full effect. In real-life crime scenes, investigators have to take care to apply it evenly, because blood traces can appear more concentrated in areas that receive more spray.
The chemical is a great tool for finding even tiny traces of blood, and according to the manufacturer it can be used on dried blood stains that are months — and even years — old.
It may make for dramatic TV, but using Luminol alone probably won’t crack the case. Investigators have to do further forensic tests to make sure that the substance identified is actually human blood.
In fact, during the O.J. Simpson murder trial police claimed that the Luminol test performed in the Bronco confirmed the presence of blood in the vehicle. But Simpson’s defense lawyers pointed out that Luminol reacts positively not just to blood but also to substances including household bleaches, horseradish, citrus juice, watermelon, and iodine.
Hidden blood-spatter patterns can help investigators locate the point of attack, type of weapon used, and, sometimes, the presence of bloody fingerprints or footprints.
During dramatic Luminol blood discovery moments on shows like Dexter, the characters are often shown using the blue light and the Luminol at the same time. But in real life, you don’t need light to make Luminol glow. In fact, it works best in absolute darkness.
In the ID video, I show that it is possible to use a mini UV LED flashlight ($6.99, also on Amazon) to spot blood, but it will appear dark or black instead of glowing. This can sometimes make blood stains easier to spot on lighter surfaces like the bunny’s white ears.
You can also perform a party trick by showing your friends which random items in your house glow under the blue UV light. These include Irish Spring soap, glow sticks, and tonic water.
Of course, the blue light will also make semen and other bodily fluids glow — so the most frightening revelation could be the moment you point it at your sheets on laundry day.
Main photo: Catherine Townsend demonstrating Luminol in DIY CSI video [Investigation Discovery]