One of the first synthetic pigments humans came up with was used in Ancient Egypt. Now it could help solve contemporary crimes.
Egyptian blue – also known as calcium copper silicate - is found on Egyptian artefacts dating back to around 3000BC. It was used throughout the ancient world to colour statues, pots, beads, and inlays.
But now researchers have discovered the bright blue powder has another quality that makes it perfect for fingerprint dusting – namely, it glows.
“It doesn’t glow in the visible part of the spectrum, that you and I can see,” says Professor Simon Lewis from Curtin University. “But that’s okay, because a camera can be very easily modified to detect infrared luminescence.”
Very few substances glow in the near-infrared (NIR) spectrum, and this means the pigment can help shed new light on particularly tricky fingerprints. The study was recently published in Dyes and Pigments.
Dusting for clues
Even though it’s not without issues, fingerprinting is still a critical part of forensic investigation, says Lewis. “Even in this day of DNA – it’s still very, very important as a complimentary technique.”
Prints can provide accurate evidence that there’s an association between people and places or objects, but the images need to be high quality. These days most fingerprints are detected by using black or white powders, which help provide a contrast against the surface, but it doesn’t always work.
“Imagine if you had a white or black dust for a highly patterned surface,” explains Lewis. “These are quite challenging.” Very shiny surfaces also make fingerprint detection difficult.
Since most things don’t glow when you shine white light on them, dusting with a luminescent powder can reveal previously unseen prints with particularly high contrast.
While testing Egyptian blue, the researchers reduced the size of the particles, which greatly increased image quality.
“The [smaller] particles could actually stick properly to the fingerprint, to give us the fine detail. And then we got those fabulous pictures,” explains Lewis.
Art meets science
The research was a collaboration between forensic experts at Curtin University, and conservation scientists at the Indianapolis Museum of Art (IMA).
Dr Gregory Smith from the IMA has been using NIR imaging to identify Egyptian blue pigment on ancient artefacts for years.
“I’d always wanted to investigate Egyptian blue for fingerprints, because it exhibits strong photoluminescence in the NIR region,” Smith explains. He knew Lewis had been working on fingerprinting, and called in his forensics team.
The luminescent dust isn’t designed to be used at the crime scene. “The idea is that you might have objects brought back to the laboratory to be processed,” explains Lewis.
He adds that there is still further work to be done: “We need to use a much wider range of fingerprint donors, and on a wider range of surfaces. [But] this is proof of concept.”
Even though it’s not the first luminescent fingerprint powder, Egyptian blue consistently outperformed commercial powders by highlighting ridge detail, and avoiding interference from the surface.
Researchers are confident that ancient art could still provide more clues to help solve modern mysteries.
“In the art world at the moment, there is increasing interest in looking at other pigments that have interesting properties that we could look to, and maybe come up with other forensics solutions,” says Lewis.