Laser ablation treatment of soiled featherworks: The first validation study

Abstract

• Laser cleaning is effective and controllable to remove soiling from featherworks. • Feathers tested herein showed an unexpected high stability under laser irradiation. • In the optimal fluence range no relevant modifications were detected. • Longer pulses by Nd:YAG (1064 nm) laser provide a more gradual action than shorter ones. • With one laser treatment simultaneous cleaning on both sides of a feather is achieved. While laser treatments gradually spread in conservation, there is a growing interest on their application to the removal of soiling from fragile artefacts made of organic fibrous materials since direct and/or long term undesired effects have been observed when using traditional cleaning techniques. In this work, fiber-coupled Q-Switched (QS) and Long-Q-Switched (LQS) Nd:YAG (1064 nm) lasers were comparatively tested in order to define the restoration procedure of a heavily soiled 17th Brazil Tupinambà feathered cloak mostly made of scarlet ibis feathers. As assessed using fluorescence and Vis-NIR micro-spectroscopy, safe single-pulse removal thresholds were about 0.12 J/cm 2 for QS and 0.4 J/cm 2 for LQS, while microstructural damage was observed at 1 J/cm 2 and 5 J/cm 2 , respectively, thus evidencing a significant selectivity potential. Undesired effects were thoroughly investigated also considering the dependence on the pulse repetition frequency and number of pulses, in order to determine the optimum irradiation parameters in view of the extensive laser treatment of the present artefacts. Furthermore, analytical characterizations using SEM and contact-angle measurements allowed demonstrating that no any microstructural change occurred below the alteration fluences measured. According to these results, an overall laser-based dry cleaning methodology including laser ablation, paper sheets to collect removed soiling particles, and continuous particle suction by low pressure table and hoods was defined and successfully carried out. The laser-based restoration and associated systematic analytical characterizations of the present Brazil Tupinambà cloak represents the first validation study on laser ablation treatments in conservation of featherworks, which offered the opportunity to approach related general methodological aspects concerning the characterization of laser-induced effects, threshold definitions, and operative fluences.