It’s the stuff of Marple and Poirot: the dark contours of a detective in the shadows, leaning over a table with a magnifying glass firmly in hand. At over one hundred-years-old, it’s certainly one of the the oldest disciplines within forensic science. Contrary to popular perception, fingerprinting as its own field has evolved tremendously since then. We’re a long way from prehistoric picture writing where people stuck their thumbs in clay or even those filed fingerprint sheets from the late 1890s.
This isn’t to say some of the more conventional methods have been completely abandoned. Fingerprints, the most commonly-used forensic evidence all over the world, can be recovered in multiple ways according to surface or substrate — some approaches are more traditional, and some are decidedly dependent on modern technology (as is the case with national fingerprint databases). In any case, wherever you’ve left them, there’s probably a way to find them (shouldn’t make you nervous, right?)
If you’re ready to embark on your own personal investigation, we’ve reviewed five innovative ways to lift fingerprints (and detailed when and where to use them, for maximal recovery).
Detective work, Sherlock, not a chore: dusting for prints.
Despite what impression you might get from TV crime shows, it’s not as simple as getting out your bristly brush and sweeping it across any old wine glass or paper-filled bureau. There’s a method to sampling and recovering fingerprints in a crime scene — where an investigator has the daunting task of lifting impressions from any surface potentially involved.
In all cases, remember this: fingers are coated with perspiration (or sweat, to be simple about it). All the oiliness of your stubby little digits create latent (or invisible) prints on everything you touch, leaving behind a little piece of you as you go about your everyday life. That’s the stuff that powders pick up.
Dusting involves some sort of implement — anything from a squirrel-hair or fibreglass brush, to a magnetic wand — and a powder, like aluminum or magnetic powder (the “oohs” and “aahs” we get when we’re demonstrating how the latter works during workshops is always something to anticipate). The movement you make with your wrist depends largely upon the surface, the tool and the powder you’re utilising for the task.
Cyano-what? Superglue fuming.
The story behind this one is kind of a gem. The idea of recovering fingerprints with superglue wasn’t a genius suggestion — it was more like a happy accident. It all started with a guy named Fuseo Matsumur (an epic name, if you ask us) who was a hair and fiber expert in Japan. One particular workday, he was tasked to glue hair samples from the crime scene for routine microscopic examination.
It wasn’t too long before he noticed his own powdery but detailed fingerprints becoming visible on the edges of the slides he was using. He became the first to determine that using fumes from the Superglue (or cyanoacrylate adhesive) constituted a reliable fingerprint recovery method. Unsurprisingly, using a cardboard box, a well-ventilated area and some superglue — it’s not all that difficult to repeat his findings.
Another kind of bullet fingerprint.
Ever in a situation where you need to develop fingerprints from a bullet casing or bomb fragment? We didn’t think so. If you ever do find yourself in this unlikely situation, we’ve got precisely the approach you’ll need to determine whodunnit — safely and accurately. Very recently (think 2008), scientists developed a method which relies on the subtle corrosion or breakdown of metal surfaces to determine what a given impression looked like.
Chloride ions in our sweat acts like a chemical agent against casings; and of course, these ions are present in our sweat — which is how we leave latent prints. If you can take a closer glimpse at the part the ions corrode, you can visualise the patterns. Access to 2500 volts means you can pass an electric field through the metal. Add some fine conducting powder to the mix, and it’ll stick to the corroded areas.
Lighting them up: prints that glow.
Electroluminescence not only looks spectacular under the right kind of microscope, it’s also the most recent method to recover fingerprints (the announcement was only made in August 2012). A given fingerprint is pressed onto an electrode which is either composed of indium tin oxide or a stainless steel sheet. Then, the electrode is immersed into a special chemical solution. When a voltage is applied to the electrode, the fingerprint lights up — giving off a wondrous and luminescent glow that shows the impression in exquisite detail without any damage.
It’s a harder technique to replicate, we’ll give you that — but still, pretty cool.
Your Turn: Know another sensational way to recover prints? Ever tried lifting your own fingerprints, at home, at school — or are you an expert in the laboratory? Let us know in the comments. We’d love to hear from you.