Interaction between historic painting materials. Benefit of applying spectrometric techniques and principal component analysis

Abstract

This PhD Thesis studies historical painting materials, the interaction among their chemical constituents and the deterioration caused by accelerated ageing processes by their exposure under diverse environmental conditions. The use of routine and advanced analytical techniques applied to the study of painting materials was evaluated by multivariate analysis method (Principal Component Analysis; PCA). The aim of this work was to demonstrate the ability of spectrometric techniques and PCA to discriminate painting model samples according to their differing composition, states of ageing or the interactions among the different components of the painting materials. To this end, different inorganic pigments and proteinaceous binders were used to reproduce model samples similar to real tempera paintings, used historically in the decoration of wall paintings in monuments or in canvas. The final goal of this investigation was to study the behavior of the pigments and binders when they are mixed, and their mineralogical and chemical stability to examine their compatibility in real painting samples. In this regard, a novel analytical approach was applied to identify inorganic and organic components from polychromes from the 14th century Islamic University, Madrasah Yusufiyya, in Granada (Spain). This study shows the benefits of characterizing historic paintings via compositional and microtextural data from Micro-X-Ray Diffraction combined with molecular information acquired with Raman Microscopy along depth profiles in paint stratigraphies. Also, information obtained give insights regarding the manufacture of pigments, decay processes and the painting technique. This information was used to discriminate between the original Nasrid paintings and Christian historical interventions. This PhD Thesis represents an advance in the field of Cultural Heritage Science and particularly in studying historical tempera paintings. It shows for the first time the potential benefits of the application of PCA to identify historical pigments and proteinaceous binders on tempera model samples and to study their physico-chemical interactions.