Laser Cleaning Methodology for the Preservation of the Porta del Paradiso by Lorenzo Ghiberti

We investigated the optimisation of the laser cleaning parameters for the conservation of the Porta del Paradiso, gilded bronze masterpiece of the Florentine Renaissance. Photothermal and photoacoustic regimes involved in the ablation dynamics by Nd:YAG lasers with different pulse durations, were modelled on the basis of preliminary stratigraphic characterisation and irradiation trials. The physical analysis was aimed at understanding the nature of the ablative process and at estimating the thermal wave coupled into the gold film. This allowed the selection of a suitable pulse duration range to achieve a high discrimination level, thus optimising the cleaning result. The analytical description here reported also contains general results, which could be exploited in other conservation cases of gilded bronzes.