Non-destructive dating of ancient flax textiles by means of vibrational spectroscopy

The possibility to define a two-way relationship between age and a spectral property of ancient flax textiles has been investigated in the present paper employing both FT-IR and Raman analyses on selected samples dated from about 3250 B.C. to 2000 A.D. After a first selection to eliminate polluted samples, based on visual inspection, on proper mechanical tests and on a first glance at the resulting spectra, eleven samples of the original 14 have been used for Raman analysis and eight for FT-IR analysis. For the first time, the possibility to define a correlation among spectral properties and age of flax samples, by using calibration curves, has been proved. In agreement with the kinetics theoretical model, the experimental relationships are of an exponential type, giving correlation coefficients higher than 0.9. The better results were obtained using FT-IR because Raman analysis needs to consider an additional variable due to the non negligible influence of fluorescence. Presently, the method allows to assign an uncertainty of centuries to the measured data, but future calibrations based on a greater number of samples (though it is not easy to find ancient samples adequate for the test) and coupled with ad-hoc cleaning procedures could significantly improve its accuracy.