This paper describes the first systematic analysis of the palette of Francesco Hayez, one of the most outstanding artists of European Romanticism, whose painting technique has never been extensively investigated despite the plethora of artistic studies. He lived in a particular moment in the history of painting, as in the first half of the 19th century many synthetic pigments were available, also in tin tubes, but traditional materials were still used. Sixteen paintings on canvas and on panels, created between 1823 and 1868, were analyzed in situ through non-invasive techniques (infrared reflectography and infrared reflection spectroscopy). Imaging investigation provided clues on painting technique, revealing some cases of pentimenti and underdrawings. A preliminary survey was carried out on a hundred pure pigments used up to the 19th century and on new synthetic colours, in order to attain reference spectra for the interpretation of painting spectra. The portable infrared instrument provided insight into Hayez's painting materials, identifying barite, ivory black, lead-tin yellow, Naples yellow, ochres, Prussian blue, and white lead. The pigments were often blended, to obtain a unique fabric appearance or to attain cold shades. The results pointed to a siccative oil as a binder, mixed with white lead so that it could act as a catalyzer in polymerization reactions, and in some cases with a proteinaceous binder and resins. The preparation was made with gypsum and white lead mixed with a siccative oil. The results showed that the artist used a typical traditional palette, throughout his career, in order to lead to brilliant colours and with long-term stability. Anyway, the possible presence of cobalt blue in a few paintings suggests that Hayez had probably started testing the new colours, since the second decade of 19th century.

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This paper presents the study of four gypsum mixtures, focusing on the role of both inorganic and organic additives and on the micro-structural features and mechanical properties. Additives have been chosen among those most reported in historical recipes, for example magnesia, lime putty, rabbit glue. The selected mixes refer to gypsum-based materials used in artworks manufacture, such as plasters, mouldings, stuccoworks, pastiglia. Blank reference materials were prepared on purpose according to the specific recipe, in order to verify the final composition and to highlight the hardening mechanisms and the formation of setting compounds. The chemical composition was related to workability properties and final mechanical resistance and the action of additives as retardants was studied with interesting results. For instance, MgO imparts good properties to the mechanical features, especially with regard to the compressive strength characteristics.

In this study, the microstructure of mock-up mortar specimens for a historic environment, composed of different mixtures, was studied using mercury intrusion porosity (MIP) and microcomputed tomography (µCT), highlighting the advantages and drawbacks of both techniques. Porosity, sphericity, and pores size distribution were studied, evaluating changes according to mortar composition (aerial and hydraulic binders, quartz sand, and crushed limestone aggregate). The µCT results were rendered using 3D visualization software, which provides complementary information for the interpretation of the data obtained using 3D data-analysis software. Moreover, µCT contributes to the interpretation of MIP results of mortars. On the other hand, MIP showed significant ink-bottle effects in lime and cement mortars samples that should be taken into account when interpreting the results. Moreover, the MIP results highlighted how gypsum mortar samples display a porosity distribution that is best studied using this technique. This multi-analytical approach provides important insights into the interpretation of the porosimetric data obtained. This is crucial in the characterization of mortars and provides key information for the study of building materials and cultural heritage conservation.

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