Structural evaluation of restoration processes with holographic diagnostic inspection

Abstract Implementation of laser technology in art conservation has resulted in an increased consideration of intervention restoration processes. Skepticism is raised regarding the side effects of interactions that could induce either short- or long-term irreversible physical alterations. Herein, an integrated laser-optic module based on the principles of holographic interferometry (HI) has been developed to study existent structural condition and probable alterations. The experimental procedure involved allows repeatable data acquisition in long-term monitoring. The tested system and methodology overcome a fragmented structural approach imposed in art conservation diagnostics by existing instruments and practices, and a full field response offering a detailed source of information is obtained. The controlled procedures by which interference fringes are formed by laser cleaned surfaces permit their long-term comparison. The results urged studies on the fundamental mechanical behavior of defects. Thus, the high resolution of HI recording was used to study the dynamics of deterioration by detecting the potential of existing defects’ natural propagation, which for the first time is described here. The study can form the basis to distinguish natural from artificially induced alterations. Comparative evaluation during conventional conservation consolidation processes was performed on an early El Greco painting which resulted in a direct evaluation of the restoration action. The results thus far were acquired in laboratory facilities. A custom-developed system was next transported to the museum floor and a significant outcome of on-field holography complementing established structural conservation diagnostics was accomplished.