A Methodological Approach for Multi-Temporal Tracking of Silver Tarnishing

Silver tarnish manifests by changes in the optical properties of the material. Documenting these changes creates many challenges for imaging techniques. This paper proposes a methodological approach based on processing Reflectance Transformation Imaging (RTI) data for tracking multi-temporal changes on such surfaces. Through the statistical analysis of the surface's angular reflectance, information related to the appearance attributes can be evaluated and visualized by maps. Thus, this paper explores the global surface change of the reflectance response of silver tarnishing as a function of time. A qualitative and semi-quantitative evaluation is based on multivariate distance measurements at different time intervals. The results are compared to surface change evaluation by visual inspection, photographic documentation, and colourimetry, practices traditionally used in conservation documentation to monitor surface changes over time. The outcome of this research illustrates the possibilities of RTI data analysis as a tool for accurate multi-temporal documentation of the optical properties changes on specular surfaces