Protein power

Mass spectrometry-based proteomics is a relative newcomer to the field and is capable of providing a thorough and very detailed characterization of any protein residues present in a given sample, as well as any accumulated damage. The technique is so sensitive that less sample material is needed compared to other methods. And unlike, say, gas chromatography-mass spectrometry, it’s also capable of characterizing all proteins present in a sample (regardless of the complexity of the mixture), rather than being narrowly targeted to predefined proteins.

In 2023, scientists used this approach to discover that beer byproducts were popular canvas primers for artists of the Danish Golden Age. And earlier this year, we reported on the identification of proteins from fingerprints of Renaissance people rifling through the pages of medical manuals, revealing more about how people constructed hands-on knowledge in that period.

For this latest study, the authors took tiny samples from several Egyptian artifacts housed in different collections in Sweden, the UK, and Denmark, dating between 1425 BCE to 400 CE. These included painted wooden coffins, wall painting fragments from a tomb, painted plaster used to make a mummy bust, and painted limestone architectural elements. In addition to those samples, the team also analyzed blank negative control samples and examined the chemical damage to all detected proteins in order to exclude the possibility of laboratory contamination from the final results.

The results confirmed that ancient Egyptians frequently used cow glue, as well as collagens derived from sheep, goats, horses, donkeys, and antelope. Those materials were most likely prepared by boiling animal skin and connective tissue. These weren’t just found in adhesive samples, but also in samples of paint and ground layers, suggesting that Egyptians chose their materials based on ready availability. “No notable correlation was observed between the choice of the animal species/part and the object type, the nature of the application, the color, the chronology, the geographical origin, or the use context (funerary or palatial),” the authors wrote.