Preliminary Results of the Er:YAG Laser Cleaning of Textiles, Paper and Parchment

Abstract

The main constituents of textiles, paper, and parchment are proteins and polysaccharides. These organic materials are particularly sensitive to damage such as spotting, dimensional deformations, and depolymerization and offer a surface particularly suitable to the deposition of various materials. In the case of paper and parchment cleaning, traditional techniques are well known, as well as the risk of making halos and shades when using the mechanical action of a scalpel or solvent mixtures to thin the spots. For textile artifacts, dust, spots, and mud residues must be removed, though this action is quite difficult with traditional methods, because the dense weft and warp structure does not allow a complete cleaning without minor damage to the artwork. The authors set up a research program to verify the possibilities and results of Er:YAG laser equipment, emitting at 2,940 nm, following the results achieved previously at the Opificio delle Pietre Dure in the treatment of organic materials (LACONA IV proceedings). The wavelength and the uniform fluency distribution were chosen in order to respect the delicate organic material. The first step for both paper and textiles was to determine the safety threshold for the constituent materials; thereafter, the efficiency of the simple laser pulse or the pulse absorbed by wetting agents (such as water, alcohols, and other organic solvent mixtures) was tested. Particularly, the study wanted to determine the cleaning efficiency, the laser-induced changes in the morphology, and chemical composition of the laser-exposed surfaces. The study of these effects on the surfaces, before and after the Er:YAG laser treatment, was performed by using optical microscopy, scanning electron microscopy, Fourier transform infrared (FTIR) and µ-FTIR, and gas chromatography-mass spectrometry techniques. The results obtained show that the materials can absorb a small amount of energy, which is sufficient to remove dust and spots without change or damage. For textiles, due to the complex structures of fibers and yarns, a multistep laser cleaning that exposed the surface several times to a very low energy gave the best results without any damage.