L’uso di laser QS Nd:YAG nella conservazione di manufatti etnografici realizzati con fibre di palma dum

Before restoring ancient and valuable ethnographic objects many aspects should be taken into account, because lignocellulosic fibers-based materials undergo different and concomitant degrading reactions (oxidation, hydrolysis, depolimerization) over time. Basically, dry cleaning methods should be preferred, as they are potentially less invasive in the long term, especially for the easily hydrolysable components. Here, the fundamental and second harmonic of Q-Switch Nd:YAG laser, were comparatively investigated for dealing with the removal of soiling (soot, dirt, aluminum silicates, carbonaceous material) from a woven-fibers angarêb bed, which is preserved at Africa Hall of the National Geographic Society Museum (Cairo, Egypt). Besides fiber identification, laser induced-effects were assessed on angarêb fibers by means of stratigraphic examination, Vis-NIR fluorescence emission, Raman spectroscopy, ESEM-EDX analysis and optical microscopy observations. Irradiation at 532 nm negatively affects color appearance and structural integrity of fibers. Bond-breaking/depolymerization followed by bleaching, due to the significant absorption of lignin/phenolic-carbohydrate and lignin-quinonoid complexes, occur at this wavelength. The promising results achieved at 1064 nm, in term of chemical and structural integrity, highlight the possibility of using this wavelenghth for treating soiled and untreatable ethnographic material.