Subsurface analysis of painted sculptures and plasters using micrometre-scale spatially offset Raman spectroscopy (micro-SORS)

A recently developed variant of spatially offset Raman spectroscopy (SORS) for the non-invasive analysis of thin painted layers, micro-SORS, has been applied, for the first time, to real objects of Cultural Heritage - namely painted sculptures and plasters. Thin layers of paint originating from multiple restoration processes often applied over many centuries have been analysed nondestructively using micro-SORS to depths inaccessible to, or unresolvable into separate layers, by conventional confocal Raman microscopy. The concept has been demonstrated on several artistic artefacts of historical significance originating from Italy and dating fromthe medieval to the 18th century. The technique extends the depth applicability of Raman spectroscopy and with its inherently high chemical specificity that expands the portfolio of existing non-destructive analytical tools in Cultural Heritage permitting to avoid cross-sectional analysis often necessitated with this type of samples with conventional Raman microscopy. Currently, the method is non-invasive only for artworks that can be placed under Raman microscope although there is a prospect for its use in a mobile system with largely removed restrictions on sample dimensions.