A Multimodal toolkit to assess sculptures conservation state
Résumé
The preservation of sculptures relies on the accurate knowledge of their conservation state. Yet, the technical documents available to the curators (e.g. discovery or restoration reports) gather information mainly relating to the surface condition. However, some degradation mechanisms affect the constitutive materials at the core, without necessarily presenting superficial symptoms. We therefore propose an approach combining 3D imaging, semantic annotation of alterations, and non-destructive tomographic auscultation to evaluate and connect the external and internal conservation states of artworks. This approach was applied on marble sculptures as this material is particularly affected by internal decohesion and fracture phenomena due to its sensitivity to climatic variations. In fact, the studied artworks display heterogeneous states of cohesion as well as superficial cracks of unknown extension which preclude them from any exhibition project outside the walls of their original museums. Each sculpture was first modeled in three dimensions during photogrammetric campaigns. The 3D models thus produced served as support for the semantic annotation of superficial alterations. Then, acoustic monitoring campaigns were performed and algorithmic treatments provided tomographic reconstructions of the ultrasonic pulse velocity though the entire volumes. In addition, localized crack depth measurements were carried out to document the internal extension of these superficial defects. The whole set of geometric, descriptive, and acoustic data were eventually merged within a dedicated digital framework. This multimodal tool allowed combining human and instrumental analysis (morphology of artwork, surface condition, and structural behavior) thanks to a semantic characterization system. Finally, this toolkit centralizes and spatializes all elements necessary for evaluating both internal and external conservation states of the sculptures and thus the risks associated with visible and non-visible defects. It also provides interoperable documents to the curators for the monitoring of these fragile artworks.
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