Modelling and IR thermal monitoring of the laser reconversion of blackened pigments
Résumé
Some mural painting pigments tend to blacken with time due to their conversion to dark degradation products. An interesting approach of restauration involving continuous wave Nd:YAG lasers was suggested more than ten years ago, focusing on the reconversion of black plattnerite (β-PbO2) to red minium (Pb3O4). In the context of extending this approach to other pigments concerned by blackening (lead white and cinnabar), the laser heating of plattnerite was monitored by IR camera and modelled. An irradiance threshold (around 80 kW m-2) corresponding to the considered reaction temperature has been measured. A spectrocolorimetric study was conducted, which unravelled the reflectance changes occurring during the reconversion. Optical and thermal parameters of the plattnerite were measured or extrapolated to run the model. The latter was successful in reproducing the surface temperature evolution only in the first moments of the irradiation
Origine : Fichiers éditeurs autorisés sur une archive ouverte