Laser removal of mold and foxing stains from paper artifacts: preliminary investigation

In this work we focused on the laser removal of fungi growths and foxing stains from old paper artifacts. Irradiation tests have been carried out using Nd:YAG laser’s second harmonic and characterized through morphological analysis by means of optical microscopy and UV-VIS fluorescence, along with SEM-EDX microscopy. In addition, FTIR spectroscopy and VIS diffuse reflectance spectroscopy have provided, respectively, very useful information on chemical processes of the paper ageing and on the laser removal effectiveness. High selectivity and removal gradualness were observed in the treatment of metal-induced foxing (Fe and Pb), likely arising from the contact with metal objects. Moreover, similarly satisfactory results have been achieved for the removal of fungal colonies without inducing detectable structural damage to the cellulose fibers. The best operating conditions determined have been finally used in order to approach a practical conservation problem of an original engraving by G. B. Piranesi entitled Veduta del Ponte e Castello Sant’Angelo (18th century).