Understanding how the original manufacturing process affected preservation of Egyptian leather sandals over millennia
Ancient leather artefacts from Museo Egizio have been studied by combining optical and spectroscopic tools (SEM-EDS, XRF-RAMAN), more sensitive their surface composition, and neutron spectroscopy, able to better probe their bulk.
Leather was a common material in ancient Egypt and its manufacturing into sandals, bags, and stools responded to many daily applications. For this reason, leather-made objects were subject to hard use and harsh environmental conditions. While several ancient leather artefacts have been discovered, including the rich collection at Museo Egizio in Turin, the optimal preservation of this delicate material is still a matter of discussion and research. In particular, the structure of the organic components of leather, especially collagen, can be subject of different kinds of degradation.
As explained by Valentina Turina (Museo Egizio), “the focus of the present investigation was to study a set of leather specimens, dating around 1400 BC, fragmentary in nature and exhibiting strong crystallization and dehydration”. To characterize the deterioration process of these artefacts, a combination of several techniques was employed, including microscopy and spectroscopy techniques available at ISIS@MACH ITALIA (IM@IT), Unit University of Rome Tor Vergata, and at University of Messina, combined with Inelastic (INS) and Deep Inelastic Neutron Scattering (DINS), using the TOSCA and VESUVIO beamlines at ISIS Neutron and Muon Source, through the IM@IT Neutron Gate.
Measurements using Scanning Electron Microscopy (SEM), performed at the IM@IT in Rome, allowed a microscopic characterization of the surface of the samples. High quality images, using both backscattering and secondary electrons (figure 1) showed, among other features, sharp fractures in the fibrous material, possibly related to the dehydration process experienced by the leather sample.
Fig 1: images of a leather specimen obtained using the Scanning Electron Microscope (SEM), with backscattering (left) and secondary electrons (right).
Information regarding the manufacturing process of the leather artefacts, especially the tanning, was obtained using X-ray fluorescence (XRF) at the University of Messina. Valentina Venuti (University of Messina) commented that “results from XRF measurements confirmed that, depending upon different tanning techniques, different materials, including iron oxide or potassium alum, appear being deposited onto the leather surface”. Complementary details on the presence of iron oxides, tanning materials and pigments on the surface of the sample were obtained from the Raman spectra collected concurrently on the same samples.
Fig 2: XRF spectra from one of the investigated leather samples.
In addition, the presence of water on the sample surface, observed in the higher energy region of the Raman spectra, was investigated using neutron spectroscopies using TOSCA and VESUVIO. INS measurements on TOSCA over a series of samples showed the presence of bound water in a variety of atomic-scale environments. The analysis of the intensity of the librational mode compared to that of other vibrations associated to organic constituents gave an insight into the hydration level on the hydration level in the bulk of the samples. Finally, DINS data provided an absolute measurement of the amount of hydrogen within the samples per mass unit that will be compared to tabulated values for modern leather, so as to obtain information on the sample average hydration level in the bulk.
This study showed how integrated studies using complementary optical, light and neutron spectroscopies provide insightful and unique information on the deterioration process of ancient leather samples to pass on to the conservation experts of Museo Egizio to pinpoint the causes of dehydration and crystallization, from the atomic to the molecular scale, helping them to design better and longer lasting preservation strategies for the artefacts.
Further information:
Experimental Team: Museo Egizio Turin, ISIS@MACH ITALIA – Unit University of Rome Tor Vergata, University of Messina
Link to the related publication will be included soon.