**Acknowledgements**

The authors like to thank the *Museo Poldi Pezzoli* (Milan), *Museo Egizio* (Turin), *Ministero dei Beni e delle Attività Culturali e del Turismo - Musei Reali di Torino, Castle of Racconigi* (province of Cuneo) and *Polo Museale del Piemonte* which promoted the diagnostic campaign on their artworks. The authors want to acknowledge Dr Gabriele Piccablotto, LAMSA, Department of Architecture and Design, Polytechnic of Turin for sharing the emission spectra of the light sources used for the colour rendering elaborations. A special thanks to the conservators that took care of the artworks and all the staff of CCR La Venaria Reale for availability and useful discussions.
