In libraries around the world, archivists are worried about the books, maps and manuscripts under their charge. To know how to care for such historical materials, however, one must know the exact composition of the paper from which they are made. Unfortunately, papers made during various eras and in various places are composed of diverse substances, and, to elucidate what these are, one typically must use chemical analyses that destroy the sample.According to Matija Strlic of the University of Ljubljana in Slovenia, most chemical methods are exceptionally time- and labor-intensive, and some require a large amount of sample, especially for the determination of the paper’s mechanical properties, such as tensile strength.“Most methods are almost never used in conservation research for a very simple reason: The sampling requirements are prohibitive,” he said.After around 1850, changes in the paper production process led to an increased amount of acid, which causes rapid degradation of cellulose. The object in this photo is from 1909 and already is so fragile that it cannot be leafed through without risking the loss of historical substance. Researchers have developed a nondestructive near-IR spectroscopy technique to recognize endangered material such as this rapidly and reliably. Courtesy of Matija Strlic, University of Ljubljana. Strlic and his colleagues at the university and at the National and University Library, also in Ljubljana, as well as at Zentrum für Bucherhaltung GmbH in Leipzig, Germany, have developed a nondestructive method for analyzing historical paper that combines near-IR spectroscopy with data gathered using other techniques.As they report in the Aug. 15 issue of Analytical Chemistry, the investigators began with more than 170 samples of historical paper, mostly single-sheet documents and pages from books. They used gravimetry and viscometry to assess the ash content and the degree of polymerization of the cellulosic fraction of the paper, respectively. They also used an atomic absorption spectrometer from PerkinElmer Inc. of Waltham, Mass., to determine aluminum content, which contributes greatly to the acidity that destroys paper over time, as well as a UV-VIS spectrophotometer from Varian Inc. of Palo Alto, Calif., for spectrophotometric analysis of lignin content. Each technique is at least partly destructive because the paper samples must be dissolved prior to testing.They then analyzed whole samples using a PerkinElmer Fourier transform near-IR spectrometer combined with a 76-mm integration sphere from Labsphere of North Sutton, N.H. The scientists compared the data from the destructive tests with that from the nondestructive ones, using the partial least squares method, to determine whether the nondestructive near-IR spectrometry could be a viable option to archivists given a robust set of calibration data supplied by the destructive tests.They found that the nondestructive spectrometry setup works well for most of the required analyses, excluding only testing for aluminum content. In addition, the technique is limited to types of paper, such as those the researchers used, that have calibration data. For example, according to Strlic, the technique currently is not useful for transparent paper because none was included in the calibration.The group plans to continue validating the system, surveying collections of historical papers and demonstrating the method to conservators.“In order for a new product to gain wider acceptance, it needs to be tested extensively,” Strlic said.Contact: Matija Strlic, University of Ljubljana, Slovenia; e-mail: matija.strlic@fkkt.uni-lj.si.