Non‐invasive and in situ investigation of layers sequence in panel paintings by portable micro‐spatially offset Raman spectroscopy

Abstract

Nowadays, the research in conservation science is focused on developing advanced portable analytical techniques able to achieve subsurface data in situ and in a non-invasive way. Micro-spatially offset Raman spectroscopy (micro-SORS) is an emerging analytical technique developed to address the need of non-invasively retrieving the molecular composition of the subsurface compounds; however, so far, micro-SORS studies of artworks have been carried out only with benchtop Raman microscopes, precluding the non-invasive analysis of large objects and artworks in situ. Here, for the first time, portable micro-SORS was used for non-invasive and in situ investigation of art objects. The potential of portable micro-SORS is demonstrated through the reconstruction of the layer sequences in selected areas of two 16th century panel paintings, providing unequivocal information about the preparation layer spread over the panels and the pigments used in the painted layers and supplying essential information on the artist's technique.

Spatially offset Raman spectroscopy

“…Portable micro-SORS devices enable investigations in situ, which is advantageous when sampling fragments or where transfer of the object to the laboratory is unfeasible 138 . Recently, a portable micro-SORS device has been developed 139 and used for the reconstruction of the layer sequences of two sixteenth-century panel paintings in situ, providing information on the pigments used and the artist's technique 140 . Such applications require care to avoid any undue damage from the laser beam and very low laser powers are often used 141 .…”

In situ Raman spectroscopy for cultural heritage studies

“…[ 158 ] Portable prototypes for both the defocusing and full micro‐SORS variant have been designed and investigated on samples, [ 159,160 ] while a dual laser defocusing portable micro‐SORS apparatus was applied in situ on two panel paintings. [ 161 ]…”

Interpol review of paint, tape, and glass evidence 2019–2022

“…Various analytical tools were presented in the literature for the analysis of artwork and cultural heritage paints, including FTIR [ [65] , [66] , [67] , [68] , [69] , [70] ], portable microscopy, and XRF [ [70] , [79] ], SEM-EDS [ 67 , 68 , [70] , [71] ], Raman spectroscopy [ 67 , 72 , 73 ], far-infrared spectroscopy in ATR mode [ 66 ], hyperspectral reflectance imaging in the visible [ 74 , 75 ] and near-infrared, XRF [ 71 , 76 ], portable macro X-ray fluorescence [ 75 , [77] , [78] , [79] ], pyrolysis GC-MS [ 68 , 80 , 81 ], micro reflectance imaging spectroscopy (micro –RIS) [ 82 ] and time-of-flight secondary ion mass spectrometry imaging (TOF-SIMS) [ 83 ]. Botteon et al evaluated the use of portable micro-spatially offset Raman spectroscopy (micro- SORS) to analyze pieces of artwork from the 16th century [ 84 ]. Rooney et al [ 85 ] and Taugeron et al [ 86 ] assessed the utility of NMR in studying cultural heritage objects in paint layers.…”