Multi-technique characterization of adhesives used in medieval jewellery

In this work, a multi-technique analytical approach was used to characterize adhesive samples taken from medieval chef d’oeuvres jewellery, three manuscript bindings and a crucifix produced in northern Italy between the 8th and the 11th century AD, according to arthistorical evaluation and 14C dating executed on adhesives. These materials being complex mixtures, mostly of organic/inorganic nature, various analytical techniques were utilized to thoroughly elucidate their composition. A preliminary survey with portable X-ray fluorescence spectrometry (XRF), applied in situ, suggested the presence of inorganic phases. X-ray diffraction analysis was used to identify crystalline phases. Fourier transform – infrared and Raman spectroscopies were used to identify the major components. Finally, gas chromatography coupled with mass spectrometry was used to identify, in the most accurate way possible, the organic compounds present in the mixtures. The combined approach of non-invasive measurements, applied for the first time to such precious objects, and of micro-invasive techniques allowed a complete characterization of the samples, widening the present view on such poorly studied materials.