Non-destructive Consolidation Assessment of Historical Camorcanna Ceilings by Scanning Laser Doppler Vibrometry
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Non-destructive Consolidation Assessment of Historical Camorcanna Ceilings by Scanning Laser Doppler Vibrometry A. Annessi1
· P. Castellini1 · E. O. Radaelli2 · L. Jurina2 · M. Martarelli1
Received: 27 October 2019 / Accepted: 25 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This paper presents a procedure for the evaluation of the conservation state and restoration efficiency of nineteenth century camorcanna vaults based on the analysis of objective features extrapolated from non-destructive vibration testing data. The camorcanna vault in “Salone Grande” of the ninteenth century Villa Greppi in Monticello Brianza, near Milan, Italy, was chosen as an application example. Non-contact scanning Laser Doppler Vibrometry was exploited for the evaluation of the dynamic behaviour of the vault before and after rehabilitation. In the first section, the frescoed structure in question, a reed ceiling spread with mortar, is described and possible related aging problems, e.g painting detachment, are highlighted. In Sects. 1 and 2, traditional and innovative non-invasive diagnostic techniques are illustrated, with particular attention to Laser Doppler Vibrometry. In Sect.3, the case study of Villa Greppi is illustrated, reporting on the restoration intervention, the equipment used on site and how the measurements were taken. While in Sect.4 the results are shown, objective feature indices are defined and conclusions are drawn. Keywords Camorcanna · Frescoes · Restoration · Scanning Laser Doppler Vibrometry · Modal Analysis
1 Introduction The use of non-contact techniques is becoming more and more widespread in the field of the diagnostics of works of art, since these techniques are valid candidates for replacing the the restorer’s manual and visual inspection without resorting to destructive methods. Among all the existing contactless techniques, the optical ones, including Scanning Laser Doppler Vibrometry (SLDV), which was also used to detect delamination in composite materials, are the most used [1]. Castellini et al. proposed the exploitation of SLDV to identify and characterise defects in frescoes on artificially aged large walls using acoustic excitation to force the frescoes into vibration, as a restorer would do by knocking on the surface with his hand [2]. Piezoelectric actuators generating acoustic waves propagating through the material under test were used as excitaters, while an SLDV acquired the surface velocity over the target area. Defects could be iden-
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A. Annessi [email protected]
1
DIISM, Marche Polytechnic University, Via Brecce Bianche 12, 60131 Ancona, Italy
2
Polytechnic University of Milan, Milano, MI, Italy
tified as high mobility areas resonating at some specific frequencies. The technique was applied to different types of artworks (mosaics, ceramics, inlaid wood and easel paintings). Although additional studies are needed to obtain a reliable set-up, SLDV proved to be an efficient diagnostic technique [3,4]. In a further study, Artificial Neura
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