Application of shearography and the percussion method for the structural inspection of wall paintings: a case study of St. Christopher in Maria Church, Nisse

Abstract

Structural delamination in mural paintings is a complex phenomenon and is considered among the most frequent types of damage. In conservation practice, the most common technique to identify structural detachments is the percussion method. Full-field optical techniques based on interferometry, such as shearography, can provide a more scientifically substantiated evaluation of the condition of heterogeneous structures of wall paintings. The empirical nature of the percussion method was observed during the condition assessment of two medieval wall paintings in the Mariakerk, Nisse, the Netherlands. It can be argued that, to allow the formulation of specific treatment needs for structural delamination in wall paintings, accurate defect mapping and characterisation is needed. The application of shearography was believed to provide a holistic representation of the condition of the structure of the wall painting depicting St. Christopher in the Mariakerk. Preliminary comparison of the methods involved revealed a degree of matching between results obtained. Discrepancies, i.e. areas deemed extremely vulnerable during percussion testing that were not detected by shearography, are debatably caused by the misinterpretation of the acoustic response during percussion testing or the inability of shearography to detect in depth structural defects. Further research regarding shearography should focus on providing more information about the depth of structurally delaminated areas within the heterogeneous layered structure of wall paintings.

Application of shearography with thermal loading for the structural inspection of Rembrandt’s Night Watch

“…Detectable defects include delaminations, debonding, cracks and fiber breakage. In the recent decade, shearography has raised increasing interest in the inspection of artworks including paintings [8][9][10][11][12] , where it can reliably and repeatedly reveal delaminations and cracks and also exclude the human factor when compared with traditional inspection techniques (e.g., visual inspection and tapping test) 12 .…”