Positive findings for laser use in cleaning cellulosic supports

Abstract

The purpose of this work is to continue with the research task carried out by the Centro de Conservación y Restauración de Bienes Culturales on the study of laser effects in the cleaning of stone-like materials. In this paper, we want to show the first steps that have been taken in the study of Q-switched Nd:YAG laser effects ( λ = 1064 nm, FWHM = 6 ns) on cellulosic supports. The experiments were carried out on samples directly exposed to laser radiation and on samples covered with an artificial layer of dirt (carbon black and ash). Scanning electron microscopy (SEM) shows a migration of fillers toward the surface when laser fluency is increased. This effect is more pronounced on mechanical woodpulp paper. Color change is only appreciable on samples covered with carbon black. Fourier’s transformed infrared spectroscopy (FTIR) shows paper oxidation in two cases: on rag paper when it is directly exposed to laser radiation and on chemical pulp paper artificially soiled using carbon black (due to the iron and copper cationic additives and the optic bleaches found in the chemical pulp paper). The conclusion can be drawn that the results are satisfactory for rag paper and mechanical woodpulp paper with a layer of dirt similar to real dirt (ash) when using the collimated beam at fluencies equal to 79 mJ cm –2.