Recognizing ancient papyri by a combination of spectroscopic, diffractional and chromatographic analytical tools

Lignin Quantification of Papyri by TGA-Not a Good Idea

Papyri belong to the oldest writing grounds in history. Their conservation is of the highest importance in preserving our cultural heritage, which is best achieved based on an extensive knowledge of the materials’ constituents to choose a tailored conservation approach. Thermogravimetric Analysis (TGA) has been widely employed to quantify cellulose and lignin in papyrus sheets, yielding reported lignin contents of 25% to 40%. In this work, the TGA method conventionally used for papyrus samples was repeated and compared to other lignin determination approaches (Klason-lignin and acetyl bromide-soluble lignin). TGA can lead to a large overestimation of the lignin content of commercial papyrus sheets (~27%) compared to the other methods (~5%). A similar overestimation of the lignin content was found for the pith and rind of the native papyrus plant. We concluded that the TGA method should, therefore, not be used for lignin quantification.

Determination of Cellulose Degree of Polymerization in Historical Papers with High Lignin Content

Determination of cellulose degree of polymerization (DP) is one of the most commonly used methods in paper degradation studies, performed either by a standardized method using viscometry (as average degree of polymerization (DP_v)) or size-exclusion chromatography (SEC) (as weight average molecular mass (M_w)). Due to the insolubility of papers with high lignin content in cupriethylenediamine (CED), such as groundwood papers, viscometric determination is not possible; therefore, pretreatment is required to allow subsequent dissolution of the papers. In this study, the pretreatment of historical papers containing groundwood with sodium chlorite in acetic acid was investigated, which enables dissolution of the paper samples in CED and determination of the cellulose average degree of polymerization by viscometry (DP_v). Kappa number was determined to estimate the lignin content in the papers. The suitability of SEC UV-VIS analysis for determination of M_w in papers with high lignin content had been verified before it was used as a comparative method for viscometry. Using SEC, changes in the weight average molecular mass (M_w) of cellulose tricarbanilate (CTC) derivative during delignification were evaluated. The results indicate that no significant depolymerization occurred in the selected samples under the studied delignification conditions, which was additionally confirmed with determination of monosaccharides by ion chromatography. The results of the M_w determinations by SEC and DP_v by viscometry are in good correlation, justifying the use of viscometry after chlorite/acetic acid pretreatment to determine the cellulose average degree of polymerization in historical papers with high lignin content.

Paper aging and degradation monitoring by the non-destructive two-dimensional micro-Raman mapping

The aim of this research is the identification of main and common physical-chemical parameters which induce paper degradation. A simple protocol to monitor the quality and molecular structure of ancient papers under natural degradation processes was proposed. Two-dimensional micro-Raman mapping were carried out. Then, point to point, the changes of both the cellulose Raman signature and fluorescence signal intensity were analysed. Modern papers were artificially aged to simulate the natural degradation and a comparison with the trend found for the ancient paper was presented and discussed. Cellulose degradation involves different mechanisms such as dehydration, cleaving of cellulose-glycosidic bonds and glucopyranose rings oxidation, that induce a reduction in the polymerization degree. As shown by the changes of Raman and fluorescence signals and NMR relaxation times, the rate of each processes depends on the initial amount of glycosidic bonds in the cellulose amorphous and crystalline regions, respectively. All these informations are useful both to define procedures to restore old documents and also to preserve the quality of modern papers for a long-term time.

Combined Use of Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy and Fourier Transform Infrared Imaging Coupled with Principal Component Analysis in the Study of Ancient Egyptian Papyri

This paper reports the results of a spectroscopic study on the chemistry of some small papyrus fragments arising from three Egyptian excavation sites. The aim of this investigation was to verify the possibility to identify significant differences in ancient Egyptian papyri using noninvasive analytical methods, that is, ATR (attenuated total reflection)-FTIR (Fourier transform infrared) spectroscopic imaging and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Differences in both lignin and cellulose compositions, which are difficult to detect with traditional FTIR and FTIR imaging spectral analysis, were revealed by the multivariate approach, and the second derivative spectroscopy was applied to enhance the spectrum resolution. Thus, it has been possible to recognize a fragment characterized by the presence of lead and of long chain aliphatic organic compound, which are not present in the other fragments, in the ink region. These data show not only that the combination of these techniques can provide important chemical information, such as to evidence the different compositions and manufacture of each papyrus, but also that metal inks were probably used also in ancient Egyptian papyri.

FIB-FESEM and EMPA results on Antoninianus silver coins for manufacturing and corrosion processes

A set of ancient Antoninianus silver coins, dating back between 249 and 274 A.D. and minted in Rome, Galliae, Orient and Ticinum, have been characterized. We use, for the first time, a combination of nano-invasive (focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), voltammetry of microparticles (VIMP)) and destructive techniques (scanning electron microscopy (SEM-EDX) and electron microprobe analysis (EMPA)) along with non-invasive, i.e., micro-Raman spectroscopy. The results revealed that, contrary to the extended belief, a complex Ag-Cu-Pb-Sn alloy was used. The use of alloys was common in the flourishing years of the Roman Empire. In the prosperous periods, Romans produced Ag-Cu alloys with relatively high silver content for the manufacture of both the external layers and inner nucleus of coins. This study also revealed that, although surface silvering processes were applied in different periods of crisis under the reign of Antoninii, even during crisis, Romans produced Antoninianus of high quality. Moreover, a first attempt to improve the silvering procedure using Hg-Ag amalgam has been identified.