Conservation of contemporary art: Alteration phenomena in a XXI century artwork. From contactless in situ investigations to laboratory accelerated ageing tests

The present study reports the results of a combined approach in investigating the alteration phenomena on a contemporary artwork, Senza Titolo, by Nunzio di Stefano. The oeuvre, created in 2001, is composed by seven lead carved panels coated with Paraloid B72. After having being stored for several years in wood boxes, it was acquired in 2015 and, only at that time, the surface showed an evident deterioration In situ analyses, by means of contactless external reflection infrared spectroscopy (ERFTIR), have shown that the alterations products are in the form of basic lead carbonate and, surprisingly, of lead carboxylate. The presence of these products were supposedly due to VOCs attack during the storage in wood boxes. The formation of lead carboxylate, due to the interaction among lead substrate and acetic and formic acids (the major components of the VOCs mixture), was investigated through a laboratory accelerated ageing. The effect of VOCs was studied on the lead substrate, on the acryl coating and on a series of mockups simulating Senza Titolo. The combination of surface and punctual analyses, by means of ERFIR and μ-FTIR, showed that the formation of alteration products is a relatively fast process. The alteration path involves firstly the absorption of VOCs moisture on the Paraloid B72 surface, immediately followed by corrosion processes, leading to hydrocerussite, lead acetate and formate. The presence of the polymeric coating controls the transformation of lead carboxylates to basic lead carbonate. Laboratory results have consolidated those obtained by in situ contactless investigations, confirming ERFTIR as powerful tool in assessing the state of conservation of Cultural Heritage materials.