Near-infrared Fourier transform Raman spectroscopy of the mummified skin of the Alpine iceman, Qilakitsoq Greenland mummies and Chiribaya mummies from Peru

Near-infrared Fourier transform (NIR-FT) Raman spectroscopy was employed to compare archaeological skin samples of a late Neolithic man (5200 BP) preserved in a glacial field in the Alps (the Iceman), skin of fifteenth century mummies preserved at low temperature and dry air in stone graves in Qilakitsoq, Greenland, and skin samples from mummified bodies from the Chiribaya culture from the Southern Peruvian desert (1000 BP). In all the spectra of mummified skin, a progressive loss of protein amide I (1640–1680 cm−1) and amide III (1220–1290 cm−1) band intensities was found, indicating either loss of protein or changes in the secondary protein structure. Thus, the observed changes or degradation in protein structure in the samples of the 500-year-old skin of the Qilakitsoq mummy and the 1000-year-old skin of Chiribaya mummies have been observed to be broadly similar to those found in the 5200-year-old Iceman. This implies that most changes in the molecular structure of the skin take place in a relatively short time interval during the natural mummification process. The spectra of lightly pigmented Peruvian mummies showed a relatively strong peak near 1300 cm−1 and an increased intensity of the ν(CH) peak at 2850 cm−1. The band near 1300 cm−1 is characteristic of twisting and wagging CH2 vibrations in lipids and the 2850 cm−1 band represents lipid CH stretching vibrations. These spectral changes suggest an increased lipid content in lightly pigmented Peruvian mummy skin compared with contemporary skin and the skin of the mummies preserved in ice. We ascribe this increased lipid intensity in the skin of the Peruvian mummies to embalming, by which means a better preservation is achieved. In conclusion, NIR-FT-Raman spectroscopy has potential use for the non-destructive chemical analysis of archaeological biomaterial. By using this technique it is possible to assess the degree of protein degradation and also to provide an analysis of embalming materials employed for the mummification processes.