Effects of laser irradiation on artwork pigments studied by laser ablation and time-of-flight mass spectrometry

Laser ablation and time-of-flight mass spectrometric analysis of the ablation plume is used to study the different response of several inorganic pigments to laser irradiation. Lead white and lead chromate in pellets and in a binding media are studied. Lead white is compared to azurite, of similar stoichiometry. For lead white the plume composition is rather independent on laser ablation wavelength and does not show important changes after repeated laser beam exposure opposite to that observed for azurite. Ablation of lead white pellets leads to ionized and neutral Pb and PbnOmHx clusters. Much less extent of aggregation in the plume is observed for lead chromate pellets and for the lead pigments in tempera. Similarities can be found between plume composition of ablated lead white and PbO, suggesting that laser/pigment interaction involves formation of PbO, therefore providing indications of the participation of a thermal decomposition mechanism.