The Complementary Use of Raman, ATR-FTIR Spectroscopy, and Chemometrics for Investigating the Deterioration of Artificially Aged Parchment

Among the materials constituting our cultural heritage, parchment has a significant role as the substrate of many archival documents. The assessment of its state of preservation has an important benefit to conservation and delineates the adequate preventive measures that would lead to better-controlled storage and exhibition conditions in museums and libraries worldwide. In the framework of this project, artificial aging of 48 new goat parchment samples was performed to induce deterioration similar to naturally aged parchment exposed to atmospheric pollutants. Five factors have been examined: relative humidity; NO₂; SO₂; exposure time, and the order of sequential exposure to NO₂ and SO₂. Temperature was kept constant at 25°C, while the effect of the above-mentioned factors was examined at two levels (low and high). Statistics was involved in advance in the experimental design. Raman spectroscopy along with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy were used to investigate the condition of collagen in parchment. The entire set of environmental factors along with detected changes in the spectra were investigated through a chemometrics scheme involving analysis of variance (ANOVA). According to the results, the onset of collagen's secondary structure decomposition was observed. Statistical elaboration of data reveals that the two analytical methods (Raman and ATR-FTIR) function in a complementary manner related to the molecular changes and the chemical reactions that happen. In conclusion, both methods can increase their impact on the investigation of parchment degradation if they are combined with other analytical methods and chemometric applications.