Towards RBS/EBS mapping at the AGLAE facility: new means to apprehend cultural heritage materials

(1) Centre de Recherche et de Restauration des Musées de France (C2RMF) FR 3506 New AGLAE – CNRS/MCC, Palais du Louvre, 14 quai F. Mitterrand, 75001 Paris, France
(2) Surrey Ion Beam Centre - Nodus Laboratory - University of Surrey, Guildford,Surrey GU2 7XH, United Kingdom
(3) Centre de Recherche sur la Conservation (CRC) - USR3224 – CNRS/MNHN/MCC)

The non-invasive study of Cultural Heritage objects by IBA gives precious information on their provenance, manufacturing process or conservation state, which are essential issues for AGLAE users (curators, conservators, archaeologists, geologists…)

RBS/EBS is of utmost interest to investigate layers at the surface such as restoration products, degraded or corroded surfaces, metallic leaf decorations, nanoparticles embedded in a glassy matrix…
In the frame of the New AGLAE project (grant ANR-10-EQPX-22), a multi-parameter acquisition system has been coupled to a vertical magnetic deflection of the beam and an XY stage allowing sample mapping over an area of interest of several centimeters with a pixel resolution of typically 20 to 40 µm. EDS X-ray, gamma, and backscattered particle events are simultaneously recorded in list mode file used by our homemade software for rebuilding the matrix of any detector and/or re-bin the data with different pixel size off-line.

GUPIXWIN is conveniently used to extract quantitative data from the PIXE spectra recorded for each pixel of the maps. To obtain reliable depth profiling information we used the IBA DataFurnace, which is one of the “new generation” codes, able to handle RBS/EBS/PIXE data self-consistently.

In this work, we will show the methodology followed to establish a map of the thicknesses of the metallic leaf present in an ancient gilt-leather artifact. Used all over Europe between the 16th and the 18th century, these decorations were made by applying a silver leaf to leather, then covered with a yellow varnish giving a gold-like appearance. The composition and thickness of the silver leaf could be precious information in determining the provenance of the artwork as well as understanding the factors influencing the degradation of the silver leaf.

The first results obtained by RBS/EBS will be presented and the influence of various parameters from the set-up (determination of the charge at atmospheric pressure, solid angle, electronic gain…) and the target (surface and substrate roughness) on the thickness determination will be discussed.