Spectroscopy studies on conservation issues in modern and contemporary paintings

Dissertation presented to the Faculty of Sciences and Technology of New University of Lisbon in fulfilment of the requirements for the Master’s degree in Conservation and Restoration Specialization in easel painting

Modern and contemporary paintings are one of today’s grand challenges in conservation of cultural heritage. Particularly, these paintings have often been retouched using materials rather similar to originals, thus, compromising the reversibility of the overpainting. In this work, FTIR and Raman spectroscopies, assisted by optical microscopy, were used to evaluate the effectiveness and harmfulness of chemical and laser cleaning methods for the removal of overpaints. Representative mock-ups prepared with commercial paint formulations were used. The laser cleaning experiment was part of an interdisciplinary study which aims the evaluation of method’s limitations by using the most aggressive cleaning parameters. The combined use of FTIR and Raman spectroscopies could identify constituent materials of modern paints, controlling their behaviour under cleaning, while optical microscopy allowed the evaluation on surface morphology. In addition, equivalent portable equipments from MOLAB were covered as a preparation for in situ analysis. Several problems in the selective removal of overpaints were found with chemical cleaning. The laser cleaning showed better efficiency in removing them, although, some alterations occurred upon laser irradiation, for instance, binder degradation with carbon formation and titanium white alteration. The proposed spectroscopic protocol was considered useful for controlling different cleaning methods in modern and contemporary paintings.