Non-destructive spectroscopic characterization of parchment documents

Membranaceous substrates – widely found in library heritage – are truly challenging, due to the variety of manufacturing traditions, the intrinsic variability of the animal's skin and the different degradation patterns affecting documents along ageing. Moreover, when dealing with unique and delicate objects as cultural heritage specimens, sampling is never recommended and often explicitly forbidden. Aim of the research presented in this work is to achieve correct protocols for unambiguous characterization of the document's materials chemical structure and of the possible surface treatments. Experimental results allow us to evidence that the chosen non-destructive techniques (Raman, ATR-FTIR and SEM/EDS) provide a good differentiation between parchment manufacturing procedures, western with lime and eastern with enzymatic treatment. Incrustations of salts on the surface as well as superficial treatment with tannin can be clearly detected. Origin of tannin – from the surface or in ink – can also be distinguished. Choice of the better technique is sample-dependent, since preparation methods, degradation, presence of incrustations, amount of tannin, dehairing method can differently affect the spectral features. For instance, Raman appears to be the most effective molecular technique on western parchment, whereas ATR-FTIR allows distinguishing the enzymatic dehairing procedure from the chemical one.