PIXE and IRR analysis of sixteenth-century ink drawings by Luca Cambiaso and his school

Non-invasive and non-contact analyses were performed on a group of 28 ink drawings ascribed to the sixteenth-century Italian painter Luca Cambiaso and his followers. Drawings analysed in this investigation were selected from the collections of Musei di Strada Nuova in Genoa and of Museo del Prado in Madrid. Particle-induced X-ray emission (PIXE), carried out at the Centro de Micro-Analisis de Materiales of the Universidad Autonoma de Madrid and at the Universita di Firenze, provided elemental data on the inks and papers. The drawings in Genoa were studied at the Universita di Genova using infrared relectography (IRR) and optical microscopy. Elemental composition of the inks was determined by comparison with a set of certified thin standards. Elemental analysis indicates that all of the drawings were executed with iron gall ink, except for one case where a mixed carbon black and iron gall ink was used. The PIXE data showed variations in the elemental concentrations of the materials used in the various inks, indicating the use of different recipes in their production. In some cases, these differences may help corroborate stylistic judgements to confirm or deny Cambiaso's authorship and separate autograph drawings from those of his pupils or imitators. PIXE analysis was also used to distinguish the presence of retouches and later additions. In some drawings, the combined use of IRR and optical microscopy revealed the presence of a dry carbon-based underdrawing, following a working method that seems more consistent with a workshop procedure than with the drawing technique of the master himself.