Use of Gellan gel for the cleaning of graphic artworks: the case study of Diana Scultori engraving

One engraving by Diana Scultori (1547-1612), "Le Nozze di Psiche" was restored using an innovative cleaning method conceived for works of art on paper. The artwork, engraved in 1575 and printed in 1613, was affected by a structural and chromatic deterioration due to a strong oxidative degradation. Such deterioration was probably accelerated by the adhesive used for a previous lining intervention. The artwork was cleaned with Gellan gel and chemically stabilized with an alcohol solution of Borane Tert butyl ammine complex (TBAB) [1]. Preliminary analysis showed that the lining of "le Nozze di Psiche" was glued using a mixture of starch paste and animal glue. Thus, for the removal of the lining, enzymatic hydrogels were used. In particular, two Gellan gels loaded with different enzymes were applied consecutively: the first gel was loaded with Proteinase K (protease) to remove animal glue and the second with alpha-amylase (hydrolase) to remove starch paste. Monitoring of the cleaning process of "Le Nozze di Psiche" was performed by means of a non invasive cleaning and diagnostic tool, based on Gellan gel combined with an electrochemical sensor. This system is suitable to verify in situ and in a real time and a simple way the paper degradation progress, and the efficiency of the cleaning treatment [2, 3]. Using this diagnostic tool, it has been possible to know when the cleaning process was completed, avoiding lengthy and unnecessary cleaning material applications. The effectiveness of cleaning with Gellan gel and chemical stabilization was assessed quantitatively by using non-invasive reflectance spectroscopy. This approach is based on an improved version of the Kubelka-Munk theory for recovering the absorption coefficient of cellulose fibers from reflectance measurements. Experimental absorptions were fitted to theoretical absorption spectra obtained by ab-initio computational simulations of oxidized groups acting as chromophores [3]. Results indicate a large decrease of their concentration following the cleaning with Gellan gel and a minor one's following the chemical stabilization by TBAB. [1] S. Dominijanni, S. Iannuccelli, L. Micheli, C. Mazzuca, M. Missori, L. Teodonio S. Dominijanni, S. Iannuccelli, L. Micheli, C. Mazzuca, M. Missori, L. Teodonio , Atti del convegno "I giovani e il restauro. Arte nel tempo: significato, trasformazione e conservazione", edizioni Il Prato, in press. [2] L. Micheli, C. Mazzuca, A. Palleschi, G. Palleschi, Microchem J, 2016, 126, 32; [3] C. Mazzuca, L. Micheli, R. Lettieri, E. Cervelli, T. Coviello, C. Cencetti, S. Sotgiu, S. Iannuccelli, G. Palleschi, A. Palleschi, Microchem J, 2016, 126, 359. [4] A. Mosca Conte, O. Pulci, M. Misiti, J. Lojewska, L. Teodonio, C. Violante, M. Missori, Appl. Phys. Lett. 104, 224101 (2014).