Not just a pretty face: Non‐invasive X‐ray fluorescence spectroscopy was used to reveal the sfumato paint layer stacking method that was used by Leonardo da Vinci to paint the faces in seven of his paintings. A strong diversity in his technique could clearly be seen with this method.

Scanning XRF is a powerful elemental imaging technique introduced at the synchrotron that has recently been transposed to laboratory. The growing interest in this technique stems from its ability to collect images reflecting pigment distribution within large areas on artworks by means of their elemental signature. In that sense, scanning XRF appears highly complementary to standard imaging techniques (Visible, UV, IR photography and X-ray radiography). The versatile XRF scanner presented here has been designed and built at the C2RMF in response to specific constraints: transportability, cost-effectiveness and ability to scan large areas within a single working day. The instrument is based on a standard X-ray generator with submillimetre collimated beam and a SDD-based spectrometer to collected X-ray spectra. The instrument head is scanned in front of the painting by means of motorised movements to cover an area up to 300 9 300 mm 2 with a resolution of 0.5 mm (600 9 600 pixels). The 15-kg head is mounted on a stable photo stand for rapid positioning on paintworks and maintains a free side-access for safety; it can also be attached to a lighter tripod for field measurements. Alignment is achieved with a laser pointer and a micro-camera. With a scanning speed of 5 mm/s and 0.1 s/point, elemental maps are collected in 10 h, i.e. a working day. The X-ray spectra of all pixels are rapidly processed using an open source program to derive elemental maps. To illustrate the capabilities of this instrument, this contribution presents the results obtained on the Belle Ferronnière painted by Leonardo da Vinci (1452-1519) and conserved in the Musée du Louvre, prior to its restoration at the C2RMF.

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