Spectroscopic and mass spectrometry-based in-situ investigation of a 17th-century handwritten academic diploma on illuminated parchment

Abstract

In 2008, more than 300 ancient scrolls, some of which were preciously illuminated, were recovered in Chicago (USA) after being stolen and illegally exported. These scrolls consisted of private and public documents, including papal and royal, dating from the 14th to the 19th century. The scrolls were returned to Italy and 42 of them, known as the Chicago Parchments, are now preserved at the State Archives of Bari (Italy). An illuminated academic diploma from the 17th century, known as doctoratus privilegium, was among them, and it was of particular interest to restorers and conservation scientists. To identify the pigments, painting binders, and animal skin origin of the parchment, non-invasive analyses were carried out on several points using portable X-ray fluorescence (XRF), µRaman, and fibre optic reflectance spectroscopy (FORS). Gold and silver decorations were confirmed by XRF, highlighting the significance of the document. A quasi-non-invasive sampling approach was used to analyze the painting binders by applying a trypsin-chymotrypsin enriched hydrogel for in situ digestion of the proteinaceous material. The extracted binders were successfully identified as bovine and rabbit glues by both matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry (MALDI-ToF-MS) and reversed-phase liquid chromatography with electrospray ionization tandem mass spectrometry (RPLC-ESI-MS/MS). By using bottom-up proteomics, the sheep skin origin of thin parchment samples was established from very small fragments that were digested in solution with trypsin.