2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | 2009 | 2008

Imagem e matéria de objectos com valor patrimonial

Authors: Luís Carlos Gonçalves Namorado Freire

Supervisors: Francisco Gil

PhD thesis, Condensed Matter Physics PhD, Coimbra (2020)

Abstract: Throughout history, different peoples, and different cultures, used diverse materials for the elaboration of objects that today may have an important patrimonial value, including works of art preserved in institutions or museums, and others with grater dimensions such as constructions, etc. The materials that make up the outer layers of those objects and their characteristics, namely their composition, present or past, stratigraphy, degradation processes, and consequent optical properties, give them the original or present visual appearance or other, as the result of restorations or simulations. In this work, a methodology was developed that can support the analysis of the materials used, namely coatings and pigments, which allows them to be characterized, identifying their composition, stratigraphy, physical and chemical properties and possible degradation processes. The colorimetric characterization of these objects and the representation of their images is carried out, based on the reflectance matrices, with a much higher spectral resolution than the conventional representations, based on some trichromatic space. This approach involves the analysis of stratigraphy by visual observation, with the collection of samples and analysis by an optical microscope, and subsequent study of its composition, the existence of mixtures, or possible degradation processes, using techniques such as X-ray diffraction (XRD), X-ray Fluorescence (XRF), micro-Raman Spectroscopy, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) and Spectrocolorimetry. These analysis tools are important, not only to characterize techniques and materials used in each object, contributing to the knowledge of its historical and cultural value, but also to determine the colorimetric properties of the objects of study. For its colorimetric study, reflectance spectra of various objects were acquired in the form of reflectance matrices, for further processing, both for visualization (allowing the choice of visualization parameters such as tricolor coding or illuminant), as well as for manipulation, in spectral and spatial domains, of the information contained in the reflectance matrices, allowing the application of filters, that allowsimulations of alteration of the colour or texture, based on information obtained from t he original materials used in other times, or to simulate the application of restorations, reconstructions or the use of other materials, with new colorimetric or texture combinations. We propose and carry out a methodology for the simulation of spectral reflectance of pigment mixtures, based on the Kubelka-Munk theory, and also a model for the compensation of distance effects for hyperspectral images acquired at greater distances than those of “macro” images (acquired in the laboratory or in-situ) as was the case with some images of buildings in the historic centre of Coimbra. Also in the scope of calculating the estimated reflectance, is proposed and tested a model for simulations of the variation of reflectance as a function of the size of the particles that make up a surface. The set of procedures developed and implemented in this work, represents a new approach, presenting a contribution to the establishment of new tools for the study and representation of objects of patrimonial value.