An innovative survey was conducted of the collections of the historical Biblioteca Classense, located in the urban area of Ravenna (Northern Italy). The survey aimed to evaluate the current conservation state of the book collections, where 297 paper-based items, including incunabula, manuscripts and books, dating from the 14th to the 20th century, were selected for analysis. This innovative survey was carried out non-destructively by assessing degradation visually and by measuring NIR spectral data followed by multivariate data analysis. Chemical and physical paper properties, important for paper characterisation and implementation of conservation strategies were determined, including paper type, pH, degree of polymerisation (DP), tensile strength, lignin, protein, and rosin content. This survey provided a significant quantitative dataset for rag paper covering a 600-year period. The analysis of DP changes over time allowed the first experimental estimation of the rate constant for historical rag paper, i.e., (4.2 ± 0.6)•10 −7 year −1 , which was validated with predictions based on the Collections Demography dose response function for historic paper taking into account the past climate in Ravenna. Statistical methods were employed to describe the correlations between the measured variables and different features of the books, suggesting that the degree of polymerisation can be used as a general proxy for rag paper mechanical strength.
The chemical and physical properties of 19th and 20th century Chinese papers were investigated using a variety of material characterisation methods. A reference collection of 178 Chinese papers, dating from 1799 to 1990 was used, and properties such as pH, degree of polymerisation (DP), lignin content, and tensile strength (zero-span) were determined. Most of the papers were of approximately neutral pH, had a low lignin content and DP similar to pre-19th century European rag paper. It was found that the high inhomogeneity and the typical paper thinness affected tensile testing and as a result, a modified method for zero-span tensile strength test was developed. Using near infrared spectroscopy (NIR), proof-of-concept partial least squares (PLS) applications were developed for determination of tensile strength, pH, DP and for dating of the samples. For the latter, using post-1900 papers, the error of cross validation was 13 years. The presence of lignin was modelled using linear discriminant analysis (LDA), where the model could distinguish between high and low lignin content with 88% accuracy. Using one or multiple sheets for transmission NIR spectroscopy led to PLS results of similar quality, which was attributed to material inhomogeneity.
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