Development of a diagnostic and cleaning tool for paper artworks:. A case of study

Wet cleaning of ancient papers is one of the most delicate and important steps in a restoration process. It allows to improve the optical quality of a graphic work as the removal of pollution and of organic substances resulting from cellulose degradation. Nevertheless, washing by immersion – the traditional process – usually involves a substantial impact on the original morphological structure of paper and could be dangerous for water sensitive inks and pigments. Furthermore it is very important that the time of the cleaning process is optimized in order to remove all contaminants, thus minimizing invasive treatments and time costs. In this contest, we have developed an innovative and non-invasive cleaning and diagnostic tools, based on a hydrogels combined with electrochemical sensor, suitable to verify in situ and in a simple way the paper degradation progress, and the efficiency of cleaning treatment. More in detail, the wet cleaning technique is based on the use of a rigid hydrogel of Gellan gum. This gel is able to gradually release the water and also to absorb the water-soluble degradation products present on the paper. Moreover, it is rigid and therefore its application and removal are fairly simple, not leaving residues on the paper surface after treatment. It could be easily combined with selective electrochemical biosensors, suitable to monitor the cleaning process. Using this new tool (a biocompatible hydrogel and an electrochemical sensor) it is possible to know when the cleanup process is completed, avoiding lengthy and sometimes unnecessary cleaning material applications. Here we report the results obtained by applying the proposed system to the “Breviarium Romanum ad usum Fratrum Minorum”, a breviary of the 18th century, highlighting the advantage and the potentiality of this new tool with respect to the traditional old paper cleaning methodology. To perform a complete characterization of the proposed system, several invasive and non-invasive techniques, such as spectroscopy, scanning electron microscopy, high-performance liquid chromatography analysis and pH measurements have been used.