Spatio-temporal monitoring of the microsurface modification in artworks under environmental forcing

Despite the valuable role of surface metrology in engineering, its potential in heritage science remains to be fully recognized. The reasons for this are evident: A hand-made artwork is a complex object with a hand-processed surface and non- homogeneous micro-geometry, subjected to different external stimuli. This study analyses the surface topography of artworks under environmental forcing and proposes a method for the spatio-temporal monitoring of its modification at the micrometer scale, using surface metrology parameters and multiscale techniques. It extends beyond the use of single roughness parameters, with a particular focus on the computation of the power spectral density function of the surface height dataset for estimating the contribution of the different spatial wavelengths to the acquired surface texture signal. As a proof of concept for the practical application of the spectral-based technique, we present two exemplary case studies that evaluate the effect of climate-induced variations on the surface of the artwork. The underlying hypothesis is that the dynamic interplay between scales in climate creates a dynamic interplay at the local scale, with cumulative effects on objects. The first case study focuses on the modifications induced by long-term artificial microclimate variations on bronze mock-ups. The second case study investigates the microclimate shock induced on an ancient parchment from the early eleventh century. This parchment was moved from the vault to the (unclimatized) consultation room in the Capitolare Library in Verona, which is the oldest still active library in the world.