Time-resolved photoluminescence imaging for the mapping of weakly luminescent pigments in paintings

UV–Vis-induced luminescence techniques are commonly employed by conservators and restorers to examine cultural heritage objects in a non-invasive manner. Many chemical components in artworks show luminescent emission, which can be used for both diagnostic and conservative purposes. The emission spectrum and lifetime are precious indicators of the fluorophore nature and the combination of these information enhance the analytical power of the technique. In this work, we propose the combined application of photoluminescence lifetime imaging and time-gated hyperspectral imaging to estimate the lifetime of the emitters and reconstruct their spectral emission at the different timescales in paintings. The combination of these techniques allows the in-depth characterization of the emission properties of luminescent materials, further providing their spatial distribution in the analysed area. The approach was initially assessed on different model paints to identify and characterize which show optical emission, and subsequently, on different historical paintings. Therein, we demonstrate how the time-resolved imaging approach is highly effective for the identification and mapping of weak luminescent pigments in artworks. In particular, we show how the faint emission from lead white paints can be detected by exploiting its long-living emission (with a lifetime of hundreds of microseconds), despite the presence of other strongly fluorescent materials such as varnish, binders and brightly emitting luminescent pigments.