Characterization of mercury gilding art objects by external proton beam

The fire gilding is one of the methods used by the ancient goldsmiths to obtain a rich, metallic glow and durable golden appearance in ornamental objects. This layer is characterized, among others, by its thickness (several microns) a diffusion profile and a Hg content (between 0 and 21 wt.%) depending on the temperatures achieved during the process. Gilded sacral art objects dated from the XVI to the XVIII centuries, belonging to the Casa-Museu Dr. Anastácio Gonçalves Collection (Lisbon) were analyzed using the external ion microprobe at Nuclear and Technological Institute, Lisbon. The average concentrations of the homogeneous areas were calculated with GUPIX, DATTPIXE and NDF codes showing very similar results. The RBS and PIXE spectra from the same point were collected simultaneously and analyzed together with NDF-LibCPIXE in order to find self-consistent solutions. Profile concentration on particular Au-reach points was extracted. Different Hg and Au/Ag ratio have been found in the pieces dating from different centuries.