Good Thinking

"Magic" marker helps investigators in hunt for fingerprints

The "magic" marker helps determine whether a receipt potentially containing fingerprint deposits is made of thermal paper (Photo: University of Leicester)
The "magic" marker helps determine whether a receipt potentially containing fingerprint deposits is made of thermal paper (Photo: University of Leicester)
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The "magic" marker helps determine whether a receipt potentially containing fingerprint deposits is made of thermal paper (Photo: University of Leicester)
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The "magic" marker helps determine whether a receipt potentially containing fingerprint deposits is made of thermal paper (Photo: University of Leicester)
Thermal paper reacts to the marker, changing color wherever it was used (Photo: University of Leicester)
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Thermal paper reacts to the marker, changing color wherever it was used (Photo: University of Leicester)

A "magic" marker pen developed at the University of Leicester enables forensic experts, police and criminal investigators to quickly determine whether a receipt potentially containing fingerprint deposits is made of thermal paper, with another device then used to reveal the presence of any fingerprints. The devices come thanks to the work of the suitably-named Dr Bond, John Bond, from the University's Department of Criminology.

Dr Bond's marker contains a solution of water, glycerol emulsion, and butylene glycol that reacts with the dye in the paper, changing its color to indicate thermal paper, which is commonly used to print receipts at gas stations, supermarkets, and ATMs. The conventional method of identifying thermal paper irreversibly turns the paper black and obliterates any fingerprints.

"The idea is that a small corner of the receipt could be marked with the pen," he explained. "Touching a small corner of the receipt will minimize the potential destruction of any fingerprints on the paper, helping to retain forensic evidence.”

Thermal paper reacts to the marker, changing color wherever it was used (Photo: University of Leicester)
Thermal paper reacts to the marker, changing color wherever it was used (Photo: University of Leicester)

If the paper doesn't change color, the investigators can then move to the conventional method of treating non-thermal paper for fingerprints. If it does react to the marker, another of Dr Bond's new gadgets comes into play: a device that illuminates the paper with filtered UV-A wavelength light, quickly revealing the presence of any fingerprints so that the thermal paper can be set aside for later analysis. This could be a crucial time-saver in criminal investigations where a large number of paper documents and receipts have been discovered.

Dr Bond previously devised a technique for lifting fingerprints off of metal surfaces – such as bullet casings – even if they have been cleaned, using electrical currents and a very fine conducting powder. It relied on the fact that our fingers secrete a small amount of sweat that chemically reacts to every surface we touch, and fingerprint deposits actually cause tiny amounts of corrosion on metal surfaces, with the powder adhering to these corrosion points, outlining a fingerprint.

He was also involved in research published last year of a fingerprint-imaging system that swaps traditional powder residue techniques for a color-changing film, which works with far less residue than conventional methods require and also leaves the residue unaltered for later image analysis.

Both prior developments are already in use among forensic investigators in the UK and US, and the University of Leicester is currently looking for a licensing partner to manufacture and sell this new "magic" marker in anticipation of it, too, being used in the field.

Much of the research is described in a paper published in the Journal of Forensic Sciences. Additional papers have been accepted in the same journal for later publication.

Source: University of Leicester

2 comments
David Rochlin
First of all, if you become familiar with thermal paper, you can identify it by how it looks, the weight and feel of it in your hand, lighter in weight, thinner, smoother than regular paper ( almost waxy almost glossy, but not quite. Or you could cut off a very narrow strip and apply low heat to see if it darkens. Thermal paper as we all know, would darken in our pocket from body heat, in a couple of days... The special pen is an overly cerebral, solution.
Bob Flint
Having worked with thermal imaging and printers, the paper's surface will also darken with slightest heat, just rub fingernail along an edge and it will leave a mark, so will folding and rubbing facing surfaces of the receipt can obliterate any details of payment including fingerprints, as it is often done in wallets.