The new details, when coupled together, provide the researchers with very strong evidence as to how these visages of the dead - considered to be antecedents of Western portraiture - were made.
The well-preserved mummy portraits are extremely lifelike paintings of specific deceased individuals.
Each portrait would have been incorporated into the mummy wrappings and placed directly over the person's face.
They were excavated more than 100 years ago at the site of Tebtunis (now Umm el-Breigat) in the Fayum region of Egypt.
The set is now housed at the Phoebe A. Hearst Museum of Anthropology at University of California, Berkeley.
"Our materials analysis provides a fresh and rich archaeological context for the Tebtunis portraits, reflecting the international perspective of these ancient Egyptians," said Marc Walton, lead researcher from Northwestern University.
Also Read
For example, scientists 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," Walton added.
The researchers identified the pigments used by the artists and the order the paints were applied and to which regions, as well as sources of materials and the style of brushstrokes used.
Details of the pigments and their distribution led the researchers to conclude that three of the paintings likely came from the same workshop and may have been painted by the same hand.
Working with the museum's art conservators, Walton and his collaborators used non-destructive and non-invasive techniques to extract information about the paintings' underlying surface shapes and colour.
The method was also used to determine how the artist layered the paint and to establish the order of the various pigments used in the paintings.
This knowledge will help scientists, art conservators and art historians better understand how painting techniques evolved in the Byzantine Empire (Eastern Roman Empire) and beyond.
Walton shared the details of the nearly two-year investigation at the American Association for the Advancement of Science (AAAS) annual meeting in Washington, D.C., on February 14.