Laser ablation methods for cultural heritage: restoration, conservation, consolidation

Abstract

This thesis, developed in the period between March 2012 and November 2014, focuses on the researches on new methods for cleaning, diagnostics and restoration of Cultural Heritage assets. These methods are based on the use of Laser Ablation in various media (air, water and vacuum) and on different materials, such as alloys, metals and artificial stone materials. Furthermore, the thesis proposes different types of investigation, consolidation and restoration of archaeological artefacts, introducing new possible strategies of diagnostics and enhancements in the study of cultural heritage, through the contribution of nanotechnology and nanomaterials, still slightly used in the field of Cultural Heritage. The main objective of the thesis is to verify the applicability of different techniques in different environments, also trying to make the employed methodologies less invasive and more effective. In fact, a fundamental point is LA cleaning on various materials, directly in situ, using portable equipment and prototypes can be used in subaerial and underwater environments to selectively remove of crusts and deterioration patinas that often cover archaeological artifacts. The prototype has been realized during PhD and it can be used for measurements of LA cleaning and for Raman and PL spectroscopy. For testing the diagnostic methodology efficacy, the investigations were carried out by non-destructive methods on different types of materials (such as bronze, ceramics and precious metals) in different environments (subaerial and underwater), obtaining information comparable to laboratory measurements. Morphological studies were carried out using optical microscopy, Scanning Electron Microscopy SEM and Atomic Force Microscopy AFM (rarely used in Cultural Heritage). Chemical analysis were carried out with different spectroscopic techniques including X-Ray Fluorescence spectroscopy (XRF), X-ray Photoelectron Spectroscopy (XPS), PhotoLuminescence (PL), CathodoLuminescence (CL ) and finally the Energy Dispersive X-ray (EDX). Another aim concerns the study of particulate generated by LA cleaning for application in the consolidation of the artifact and high tech (photovoltaic and optoelectronic applications). Indeed, we study the production and characterization of nanoparticles and nanocomposites based on TiO2 and SiO2 for application to restoration and consolidation in archaeological artifacts, for exploring the possibility to use NPs as consolidating materials without introducing chemical, physical or esthetical changes in artifacts. Finally, our study has demonstrated that LA cleaning does not affect the Thermoluminescence measure. This thesis develops into five chapters. In the first chapter, we will introduce the LA processes, the second describes the Diagnostic techniques and experimental setup. Instead, in the third chapter we will discuss the materials analyzed, while in the fourth chapter describes the use of by-products generated from LA for consolidation of Cultural Heritage assets and for realization of nanocomposites for high-tech applications. Finally, in the fifth chapter we will conclude the study by listing the achievements.