research profile: don't touch that paper

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n ews RESEARCH PROFILES Don’t touch that paper Imagine that you are the curator of an amazing collection of historic docu- ments, irreplaceable works of art and lit- erature. You have two questions about a particular map, which may be your most valuable holding—or a 19th-century forgery. First, is this map authentic? If the answer is yes, the next question is even more important: how do I preserve it? These questions can be answered fairly easily—all you need to do is cut a few square centimeters from one edge for analysis. But that’s unthinkable, so the process stops. Until now. A nondestructive technique for analysis of old documents, which provides details about the condi- tion of the paper as well as its age, was reported in the August 15 issue of Analytical Chemistr y (pp 6319–6323) by Tanja Trafela, Matija Strliˇc, Jana Kolar, and colleagues at the University of Ljubljana, the National and Uni- versity Library (both in Slovenia), and Zentrum für Bucherhaltung GmbH (Germany). The group used partial least-squares (PLS) analysis to relate near- and mid- FTIR reflectance data to paper properties, which were determined by classical analytical methods. These properties—ash content, lignin content, degree of polymerization of cellulose, and pH—are important for evaluating the long-term stability of the paper. On the basis of changes in the chemi- cal properties of paper as it ages, the group also developed an application for a nondestructive dating of historical documents. The research team compared its re- sults with those from destructive and chemical tests on ~170 paper samples of known age, dating from 1650 to the present. Although various analytical methods use mid-IR and Raman tech- niques, the team chose the NIR range specifically because it is information- rich, although it has low structural se- lectivity. Because real paper is often too complex to allow for an exact analytical interpretation of spectra, the researchers used PLS to correlate the spectral and chemical information. With PLS, mul- tiple variables can be considered at the same time. A key feature of the technique is speed. Archivists and librarians fre- quently must evaluate large collections to establish the current preservation state and diagnose problems that should be treated. The more valuable the docu- ment, the more important it is to know its current condition and the less likely that its steward will make it available for destructive testing. “This technique is likely to find use as a general quality- control tool in conservation workshops and in the development of new conser- vation methods,” says Strliˇc. “We also foresee similar applications for synthetic materials and for textiles.” Convincing PLS correlations were obtained for several properties that indi- cate how the paper was made and how it has aged. These properties are impor- tant indicators that conservators use to determine whether the document can be safely displayed or circulated. Lignin, for example, is a highly unstable natural polymer whose effect on paper stability is not clearly understood. Because of lignin’s limited stability in light, how- ever, the amount of polymer present af- fects decisions about whether to display a document. The most important paper property for conservators is acidity. About 70– 80% of Western library collections are rapidly degrading because of the low pH of paper produced since ~1850. The NIR analysis showed good correlation with actual destructive pH measurements. Rapid analyses will allow librar- ies to assess entire collections to determine whether books can be preserved or reproduced to save their content. Although the primary concern of the project was characteriza- tion of the papers, the correlation of the recorded data with the documents’ known ages also was striking. Clearly, the ability to ac- curately date historical documents rapidly and nondestructively will be valuable to historians. The team’s next step is the development of a portable instru- ment designed for the safe handling of objects. Curators, conservators, and collection managers from large libraries, archives, and museums will take part in this development. The SurveNIR instrument will be marketed through Zentrum für Bucherhaltung. “This will give the technique an- other advantage,” says Strliˇc. “The document does not have to come to the lab—we can carry the lab to the docu- ment. We will be able to perform rapid statistical surveys of large collections so that managers can plan for appro- priate allocation of their conservation resources.” The person responsible for that priceless artifact will still be watching nervously but breathing a bit easier. a —Steve Miller This map of the River Powhatan in New Netherlands was made by Johannes Vingboons, probably after a map made by David Pieterzoon de Vries, who made draw- ings of plantations in Virginia while sailing on that river in 1633. (Copyright Nationaal Archief, The Hague, The Netherlands.) 6436 ANALYTICAL CHEMISTRY / SEPTEMBER 1, 2007

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research profiles

Don’t touch that paper

imagine that you are the curator of an amazing collection of historic docu-ments, irreplaceable works of art and lit-erature. You have two questions about a particular map, which may be your most valuable holding—or a 19th-century forgery. first, is this map authentic? if the answer is yes, the next question is even more important: how do i preserve it? These questions can be answered fairly easily—all you need to do is cut a few square centimeters from one edge for analysis. But that’s unthinkable, so the process stops. Until now.

a nondestructive technique for analysis of old documents, which provides details about the condi-tion of the paper as well as its age, was reported in the august 15 issue of Analytical Chemistry (pp 6319–6323) by Tanja Trafela, Matija strlic, Jana Kolar, and colleagues at the University of ljubljana, the National and Uni-versity library (both in slovenia), and Zentrum für Bucherhaltung Gmbh (Germany). The group used partial least-squares (pls) analysis to relate near- and mid-fTir reflectance data to paper properties, which were determined by classical analytical methods. These properties—ash content, lignin content, degree of polymerization of cellulose, and ph—are important for evaluating the long-term stability of the paper. on the basis of changes in the chemi-cal properties of paper as it ages, the group also developed an application for a nondestructive dating of historical documents.

The research team compared its re-sults with those from destructive and chemical tests on ~170 paper samples of known age, dating from 1650 to the present. although various analytical methods use mid-ir and raman tech-niques, the team chose the Nir range specifically because it is information-rich, although it has low structural se-

lectivity. Because real paper is often too complex to allow for an exact analytical interpretation of spectra, the researchers used pls to correlate the spectral and chemical information. With pls, mul-tiple variables can be considered at the same time.

a key feature of the technique is speed. archivists and librarians fre-quently must evaluate large collections

to establish the current preservation state and diagnose problems that should be treated. The more valuable the docu-ment, the more important it is to know its current condition and the less likely that its steward will make it available for destructive testing. “This technique is likely to find use as a general quality-control tool in conservation workshops and in the development of new conser-vation methods,” says strlic. “We also foresee similar applications for synthetic materials and for textiles.”

convincing pls correlations were obtained for several properties that indi-cate how the paper was made and how it has aged. These properties are impor-tant indicators that conservators use to determine whether the document can be safely displayed or circulated. lignin,

for example, is a highly unstable natural polymer whose effect on paper stability is not clearly understood. Because of lignin’s limited stability in light, how-ever, the amount of polymer present af-fects decisions about whether to display a document.

The most important paper property for conservators is acidity. about 70–80% of Western library collections are

rapidly degrading because of the low ph of paper produced since ~1850. The Nir analysis showed good correlation with actual destructive ph measurements. rapid analyses will allow librar-ies to assess entire collections to determine whether books can be preserved or reproduced to save their content.

although the primary concern of the project was characteriza-tion of the papers, the correlation of the recorded data with the documents’ known ages also was striking. clearly, the ability to ac-curately date historical documents rapidly and nondestructively will be valuable to historians.

The team’s next step is the development of a portable instru-

ment designed for the safe handling of objects. curators, conservators, and collection managers from large libraries, archives, and museums will take part in this development. The surveNir instrument will be marketed through Zentrum für Bucherhaltung.

“This will give the technique an-other advantage,” says strlic. “The document does not have to come to the lab—we can carry the lab to the docu-ment. We will be able to perform rapid statistical surveys of large collections so that managers can plan for appro-priate allocation of their conservation resources.”

The person responsible for that priceless artifact will still be watching nervously but breathing a bit easier. a

—Steve Miller

This map of the River Powhatan in New Netherlands was made by Johannes Vingboons, probably after a map made by David Pieterzoon de Vries, who made draw-ings of plantations in Virginia while sailing on that river in 1633. (Copyright Nationaal Archief, The Hague, The Netherlands.)

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