Caracterização de cromolitografias do Livro de Horas da imperatriz Teresa Cristina por técnicas de análise não-destrutivas

Abstract

Chromolithographs from a Book of Hours, dating from the 19th century and belonging to the Imperial Museum in Petrópolis (Rio de Janeiro, Brazil), were studied by non- destructive analysis techniques. The objective of the work was to characterize colored lithographs in order to extract information for the purpose of authenticity of the work, identification of restoration interventions and assistance in possible future restorations. The book belonged to Empress Teresa Cristina, wife of Dom Pedro II who reigned in Brazil from 1831 to 1889. The techniques used were analysis of pigments by macroXRF, analysis of mirrored regions by image processing (texture descriptors and difference between similar regions) and investigation of images by multispectral photography (reflected infrared light and reflected ultraviolet light). The measurements by macroXRF were taken in situ, through a portable elementary mapping equipment, as well as the captures of the chromolithographic images made through a digital camera and an optical magnifier, under different lighting conditions. Through the elementary mapping by macroXRF it was possible to infer the presence of pigments golden bronze, vermilion, chrome yellow and Prussian blue, which proves that the Book of Hours is a work of the 19th century. The texture descriptors allowed to obtain information regarding the composition of the images and, in the three regions considered, the differences found were small with variations of around 15%, except for the contrast descriptors, which presented variations in the range of 18% to 39%. In the quantitative comparison of pixels, small variations in the order of 4% to 10% were observed between the regions compared. Therefore, it could be concluded that the artist was able to obtain the mirroring between the measured regions in a very similar way, given the complexity of the process of creating the chromolithographs. The results of multispectral photography by reflected light did not help in the identification of pigments, but allowed to infer that there were no restoration interventions and that no hidden paintings were found in the investigated regions. The analysis by incidence of infrared light was not effective in identifying nuances, since, in this spectral range, there was only omission of information in the images. In the incidence of radiation in the ultraviolet range, characteristic details were clearly evident, which are barely observable by the naked eye due to the incidence of visible light.