High-selectivity cleaning of historical paper samples with sizing through femtosecond laser ablation

Laser ablation offers cleaning method for historical and art works effectively. Difference between ablation threshold of contamination layer and the surface yields to remove contaminants from surface without detriment to historical material. In particular, lasers with ultrashort pulse duration are very convenient for brittle historical papers, fibers of which should be intact after cleaning treatment. Since duration of laser irradiation and material interaction is very short, the possibility of damage to the paper is very low. One of the other crucial issues after paper cleaning treatment is color variation on the surface. Authentic color of the historical paper has to be preserved after the procedure. In this paper, we present results of paper cleaning via femtosecond (fs) laser running at a wavelength of 1030 nm. In the first stage of this experimental study, we determined optimum laser parameters on artificially soiled and aged paper samples, then cleaned a handwritten manuscript with ‘sizing’. In calligraphy, ornamentation and miniature arts, sizing is applied on paper as a protective layer which increases strength of paper and renders it more useful. Papers with sizing have been prevalently used in Islamic or Ottoman culture. We observed that after laser irradiation, artificial soling layer is effectively removed, while original color of the subs-layers did not alter. We used scanning electron microscopy (SEM) to examine fiber integrity, and determined that the sizing layer was not removed when optimized parameters were used, thus the fibers were not damaged.