Researchers investigating 2,000-year-old mummies have discovered clues as to the methods used by ancient Egyptian artists to paint portraits of the dead.

These images would have been painted following the death of high-ranking Egyptian individuals. Showing the deceased in their prime, the paintings were combined with mummy-wrappings and placed on top of their heads.

The researchers from Northwestern University in Illinois used delicate, forensic technology to uncover the exact colours used by the artists – and even the order in which they were applied.

The study was presented at the American Association for the Advancement of Science annual meeting on 14 February, demonstrating the comprehensive yet non-invasive methods used by the scientists. The results showed that at least three of the studied portraits most likely came from the same workshop – and potentially even the same hand. The researchers say the methods used were the first to adopt modern-day painting style.

"Our materials analysis provides a fresh and rich archaeological context for the Tebtunis portraits, reflecting the international perspective of these ancient Egyptians," said lead author of the study, Marc Walton.

"For example, we found that the iron-earth pigments most likely came from Keos in Greece, the red lead from Spain and the wood substrate on which the portraits are painted came from central Europe. We also know the painters used Egyptian blue in an unusual way to broaden their spectrum of hues."

The paintings were taken from a site in the Egyptian region of Fayum; the location of an ancient Egyptian city known as Tebtunis. The site had previously been excavated 100 years ago, but the portraits were left untouched, before being moved to the Hearst Museum of Anthropology at the University of California, Berkeley.

A number of high-tech methods were used to analyse the paintings. First, sophisticated cameras took photos from multiple angles of the paintings to examine its profile.

The cameras also managed to show how many layers of paint were applied to each part of the portrait – even describing which colours were applied first.

Hyperspectral imaging data – data collected from the electromagnetic spectrum – showed the exact colours used by the artists; a technique only a few researchers across the globe use in combination with the non-invasive methods used. This was backed-up by the molecular technique, Raman spectroscopy.

"Our goal is to use objects themselves as evidence for their production," said Walton. "In our interrogation, we have used a number of cutting-edge analytical tools to uncover new and intriguing clues about how to identify the hand of an individual artist.