Sample latent fingerprint on a glass slide developed with Egyptian blue viewed in the near-infrared. (Photo credit: Ben Errington.)
Sample latent fingerprint on a glass slide developed with Egyptian blue viewed in the near-infrared. (Photo credit: Ben Errington.)

A 5500-year-old pigment known as Egyptian blue – because it was first prepared in ancient Egypt – could help modern-day forensics detect fingerprints more accurately [Errington et al., Dyes and Pigments, 132 (2016) 310].

Fingerprints can provide evidence to link suspects to the victim and/or scene of a crime because each possesses a nearly unique pattern of ridges and troughs. Detecting fingerprints on non-porous surfaces relies on the use of dusting powders, which adhere to residues from the skin left on the surface. Many materials can be used as dusting powders – from carbon black to titanium dioxide – but interest is now turning to safe and plentiful natural powders like turmeric or luminescent powders that can overcome the limitations of highly patterned or colored surfaces on which fingerprints can be hard to detect.

Now researchers from Curtin University in Australia and the Indianapolis Museum of Art believe that Egyptian blue could hold the answer. This pigment, which is actually calcium copper silicate (CaCuSi4O10), is very stable, resistant to light, oxygen, pH and temperature, and luminesces in the near-infrared (NIR) part of the spectrum.

Simon W. Lewis and his colleagues micronized Egyptian blue – reducing the particle diameter to 2 microns – and used it, without any further treatment, to dust for fingerprints on a variety of substrates. When illuminated with a regular LED white light, the researchers found that Egyptian blue readily identifies fingerprints on glass and porcelain tile surfaces.

“We found that the Egyptian blue could consistently develop the latent fingerprints, revealing good ridge detail in the NIR region,” says Lewis.

The Egyptian blue dusting powder was also put through its paces on the trickier surface of an aluminum soft drinks can – which is both highly patterned and reflective. Fingerprints can be hard to detect on such surfaces because contrast is reduced between the print and the background pattern. Egyptian blue, however, performed better than all the commercial dusting powders that the researchers compared – enabling clear visualization of the print despite the background pattern and once again providing a high level.

“The exciting thing about this [powder] is it enables us to detect fingerprints on surfaces that have been traditionally problematic with conventional powders,” adds Lewis.

The new powder could have significant advantages in general because of its stability and long-lasting luminescence. A potential drawback is that its light color after micronization and low luminescence would limit its use to the forensic lab, rather than the field, caution the researchers.

But they suggest the performance of Egyptian blue could be improved by optimizing the light source used to illuminate the fingerprints after dusting and employing a specialized forensic camera.