Then, Walter allowed the blood to dry and stain each surface for fourteen days before spraying a second solution containing luminol, sodium carbonate, and hydrogen peroxide on top.
He discovered that any areas with blood would become illuminated for about ten to fifteen minutes. And remarkably, luminol’s effects did not diminish the older a crime scene was.
Instead, Walter discovered that older blood stains would actually cause an even brighter and longer-lasting chemiluminescent reaction.
This scientific contribution was instrumental in helping crime scene investigators gain a second set of eyes. It is often difficult for authorities to spot blood spatter evidence when it is old or if perpetrators attempt to cover up their crimes.
However, if investigators are able to use luminol on the scene, the chemical can literally illuminate the events that occurred.
Like all things in life, though, luminol does have its downsides. First of all, modern luminol chemical compounds cause the blue glow to last for only about thirty seconds.
That means that investigators often reapply the solution in order to successfully study and photograph crime scenes.
Excessive reapplication, though, has been found to degrade blood samples– which can make confirmatory testing inconclusive or even impossible.
So, luminol is now used as a last resort when investigators are truly at a loss about what happened.
A second drawback involves luminol’s ability to react with other materials aside from blood– which can lead to “false positive” results at crime scenes.
Some examples of these materials include bleach, iron, and horseradish pulp.