Lead white darkening in the Varallo's wall paintings: evaluation of reconversion and stabilization treatments by µ-XANES and μ-XRD mapping

We propose to carry out µ-XRF, µ-XANES (P K-/Cl-K edges) and μ-XRD mapping to characterize micro-samples taken from wall paintings of the Italian UNESCO site 'Sacro Monte di Varallo' suffering from lead white darkening. Tests targeted at the reconversion of the pigment were performed by an established method using hydrogen peroxide and diluted acetic acid. The reconversion is temporary; therefore newly developed lead based-stabilization treatments using ammonium phosphate or ammonium oxalate were also tested. We aim to identify the series of lead-compounds formed after the tests and to monitor their chemical changes over time.