Investigation towards Laser Cleaning of Corrosion Products from Lead Objects

In this work lasers with micro-, nano-, pico- and femtosecond pulse durations were used to clean atmospheric corrosion products from the fragments of a 19th-century lead outdoor sculpture. The state of the surface was studied by optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. It was shown that for all lasers used there is no self-limiting cleaning effect, and the metal damage threshold is lower than the corrosion removal threshold. Using the XPS method, it has been demonstrated that the effect of turning a metallic lead surface blue after irradiation is associated with an interference effect in the PbO film. Raman spectroscopy indicated no phase changes in the corrosion layer after laser cleaning with 8 ns, 75 ps and 100 fs pulses, which makes these lasers useful for the layer-by-layer cleaning of archaeological objects.