Using 3D scanning to support conservation treatments for paintings

Various imaging techniques are used to visualise issues regarding a painting's appearance before, during and after conservation treatments, i.e. visible light photography (VIS) raking light photography (RAK), ultraviolet fluorescence photography (UVF) and reflectance transformation imaging (RTI). However, these techniques cannot always visualise and/or quantify conservation issues. This paper presents a new approach: colour, gloss, topography imaging (CGT). CGT's applicability as a non-invasive tool for evaluating and documenting conservation treatments in comparison to VIS, UVF, RAK and RTI is discussed. Applying this to case studies with different conservation dilemmas illustrates the technique's potential and drawbacks. CGT can visualise issues such as gloss variations, resulting from (previous) cleaning tests, (partial) varnish removal, and possibly dirt and material degradation. Furthermore, CGT can elucidate topographical issues such as bulging, and losses, and also visualise high-frequency surface variations (e.g. canvas weave and crack pattern). This results in an improvement of documenting a painting's condition, and the evaluation of treatments and their effects on the visual appearance may be quantified. In conclusion, this research shows that CGT is able to better visualise texture, gloss and colour information than existing techniques like technical photography, facilitating a more precise documentation and localisation of previous and current conservation treatments.