Long-lasting paper documents

Taking part in the consortium carrying out the project, besides laboratories from Italy, France, Portugal, Morocco, Jordan and Egypt, is the University of the Basque Country (UPV/EHU) through the multidisciplinary Consolidated Group made up of the Environmental Analytic Chemistry Group of the Science and Technology Faculty and the Restoration team of old documents at the Fine Art Faculty.

The project has three basic goals. The first is the diagnosis of the state of conservation of the old paper documents of archaeological, historical and artistic value. The second is conservation using classical methods analysing, above all, biological-type degradation processes that occur on cellulose media. The final goal is to test a new technology to reconstruct what has been lost from the cellulose-based paper medium.

When paper degrades due to chemical action it is basically because of oxidation of the cellulose of which the paper is composed. This reaction throws up a series of functional groups on which the new technology can act. As a result, a new polymeric structure amongst these degraded functional groups is formed and a series of materials that are introduced into the paper. This occurs in such a way that it forms a second coating with very similar properties to the original cellulose, but more stable. It is like new skin covering a wound.

From papyri to more modern papers

The part of the research undertaken by the UPV/EHU focuses on the analysis of the paper material, i.e. on the samples from different periods and locations, from papyri to ancient maps, official papers, newspapers from the end of the XVIII century, painted paper, and so on.

They have perfected methods for characterising these papers and what is printed/written on them. Moreover, they have been able to define and measure the processes of degradation suffered by the paper material. Currently, they are analysing to see if the new processes of conservation are really effective or not.

To carry out the analysis, the UPV/EHU researchers do no touch the samples. They employ a series of non-destructive techniques that enable analyses to be carried out without damaging the samples. The process is always similar, independently of the nature of the sample; the samples pass through the same equipment.

Three kinds of equipment

The first is the Raman portable spectrometer with a microprobe and which is equipped with a micro-videocamera to focus the laser beam on what is to be analysed, being capable of resolving to 10 micras and obtaining the corresponding spectrum. The idea is to ascertain the molecular form of the various, fundamentally inorganic compounds, in the sample of paper.

Molecular-level information is obtained with this apparatus, but with X-Ray microfluorescence the aim is to obtain an analysis of the elements in order to identify the composition of the products of the medium being analysed, thus differentiating between the original components and those extra ones that have come in to the system through some activity caused by external contamination.

Finally, an optical microscope is fitted to a micro-FTIR, in order to “see” the molecular shapes of the organic compounds. Fundamentally, the degradation suffered by the cellulose medium is verified and the nature of the aglutinants used in the writing inks or the different pigments to colour the work are analysed. Obtaining the infrared sample completes the information obtained by the other two techniques.

Once the complete information from the three techniques is obtained, the results are interpreted. To date, new methodologies on how to treat these delicate materials have been proposed. At the same time, they have made advances in the identification of the aglutinants used in inks and pigments – no easy task, by any means. We can say that the great advantage with respect to other older methods is that the damage to the sample is non-existent or minimal. Given that the UPV/EHU researchers use the infrared spectroscopic technique, which is highly sensitive with less than 0.2 milligrams of sample thickness, they can ascertain the family of aglutinants used. Knowing precisely the aglutinant used 600 years has been practically impossible until now.

Working at this microscopic scale enables identification of materials that perhaps might never have been imagined as degradation products. The problem is usually one of interpreting how these materials came to be in or on the original material. This work is undertaken applying a thorough knowledge of the impact produced by the environment or by micro-organisms and by the chemical reactivity through the use of suitable programmes of chemical balance simulation in heterogeneous phases.