Monday Mystery: The Utility of Glitter

Locard's Exchange Principle is a basic tenet of forensic work. You can read a more in-depth explanation at Wikipedia, but the most common, briefest way of putting it is: Every contact leaves a trace. It's what forensic examiners deal with when they speak of hair and fiber evidence, fingerprints, footprints, even the traces left on bullets by the rifling in the barrel of the gun they were fired from. Everything you see on CSI, is a depiction of some aspect of Locard's observation.

In light of what I've had on my mind the past couple of weeks, I feel it only appropriate to point out that glitter provides an excellent, and woefully underappreciated, demonstration of this.

Glitter is well-known to performers and crafters as 'the herpes of craft supplies'. It sticks perniciously to everything, but not quite well enough to keep it from flaking off everywhere. You wear the stuff, you leave a trail wherever you go. There is a fine haze of glitter all over everything I own right now, and it's expanded a bit into our living room, and occasionally makes incursions into Jazmin's territory.

The reason this happens is because glitter is made out of Mylar -- that is, a thin metallized polyester film. It's extremely light, and subject both to surface tension (glitter will stick to anything with a thin coating of water or lipids) and static electricity (the combination of low mass and relatively large surface area means the glitter particles will follow the opposing charge around, rather than sparking). The particles vary in size, but generally the stuff is made by subjecting sheets of colored Mylar film to some kind of cross-cutter. You can buy a small machine, if you are so bent on manufacturing your own shiny confetti that you're willing to put up with finding glitter in odd places for the rest of your natural life.

Glitter, as it turns out, looks really distinctive under a microscope. Cheap stuff generally goes through two blades; if you buy the large size, you can even see that the pieces look like wonky parallelograms. More expensive glitter, especially finer sizes, goes through three sets of calibrated blades, and comes out a much more regular hexagon. The inks used to color glitter follow the same rules as any other ink, and can be forensically analyzed. As a practical matter, most of them can be dissolved in alcohol, acetone, or butyl or ethyl acetate, which are the carrier solvents in cheap non-gel nail polish.

Down in the links is an episode of Forensic Files that goes through how examination of glitter caught the Simi Valley Rapist, and a couple of informal papers on the various properties of glitter when subject to forensic scrutiny. I'd elucidate, but my brain is jammed full of other things right now.

Check the category label for more Monday Mysteries!

Links:
https://www.youtube.com/watch?v=Akkh-CNBpFI
http://projects.nfstc.org/trace/docs/final/Blackledge_Glitter.pdf
http://infrared.als.lbl.gov/Publications/2011/VBMRB11/FSI-Glitter-2011.pdf

Comments