Spectroscopy-Driven Characterization of Degradation-Induced Changes in Sheep Parchment for Early Damage Assessment

Abstract

Introduction Parchment functioned as primary writing support for centuries until paper production was introduced at the end of Medieval times. Since parchment is mostly obtained from the dermis of various animal skins, different types of collagens form the material’s main structure. Furthermore, especially sheep parchment comprises a high fat content [1]. Considering that parchment documents are highly affected by environmental stress, e.g. light, humidity or gaseous pollutants (like SO2, NOx, O3), knowledge and early identification of degradation- induced chemical modifications of its components are important for proper damage assessment and conservation.

Methods Within this study we combine artificial aging of sheep parchments with analysis by Fourier- transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) and complementing μ-Raman spectroscopy. One sample set was exposed to artificial sunlight (295- 3000 nm) for one month. Another sample batch was aged at 80 %RH combined with 50 ppm sulfur dioxide (SO2) for one week. Subsequently, band deconvolution was performed on specific spectral regions of interests supported by multivariate data analysis.

Results Most studies on parchment degradation focus on the effects of light and temperature analyzing superficial changes of the amide I and II band or apparent formation of vibration bands after longer aging experiments. Therefore, the present work addressed parchment degradation not only induced by light but also by less studied SO2. Our approach employing non-invasive spectroscopic analysis and band deconvolution revealed changes in collagen’s secondary structure using the amide I and II bands (IR and Raman) and the so far less considered amide III band (Raman). Additional changes of the content of specific amino acids or the transition of stabilizing disulfide bridges could be further identified as early-stage signals for a progressing loss of collagen’s structural stability in the Raman fingerprint region below 1000 cm-1. The analysis of proteinaceous constituents was complemented by the detailed analysis of light- induced degradation phenomena of lipids (CH-stretching bands) in sheep parchment.

Innovative aspects • Revealing hidden signs of humidity-/SO2-induced degradation in amide I, II and III bands • Identification of degradation-indicating changes in amino acid composition and structural units • Detailed, novel spectroscopic analysis of light-induced lipid degradation in sheep parchment

Acknowledgements Parchment samples were kindly provided by Jiri Vnoucek (Kongelige Bibliotek, Denmark).