Laser Signal Dependence on Artworks Surface Characteristics: A Study of Frescoes and Icons Samples

Abstract

Use of laser-based instrumentation is gaining a wider diffusion during the conservation process of artworks, being employed in many different applications ranging from cleaning of surfaces, to chemical analysis and physical diagnostics. In this last respect, scanning laser Doppler vibrometry (SLDV) is a powerful tool to diagnose the presence of delaminations, voids and cracks in multi-layered artworks such has frescoes and icons. SLDV offers many advantages over other diagnostics techniques but, for effective operation of the instrument, a certain amount of laser light must be reflected towards the laser head. This fact poses operative limits to vibrometers due to increasing measurement distances, surface roughness and type of finishing, angle of view and reflection dependence on surface pigments. In this work we will investigate maximum distances and angles of view that still allow a clear detection of defected areas in artworks by SLDV, using frescoes and Byzantine icons prepared by professional restorers. Our results will be used in future measurement sessions to evaluate the feasibility of the diagnostics process by SLDV. Moreover we will also study the noise properties of the laser signal to determine its Power Spectral Density (PSD) and Signal to Noise Ratio (SNR) when aimed at areas with different pigments.