No abstract

Azurite is a basic copper carbonate pigment largely employed in painting realization. The areas painted with azurite are easily alterable and are often less resistant than the other parts of artworks. The azurite alteration in a black pigment, the copper oxide (tenorite), has been studied by micro-Raman spectroscopy. The blackening can be due to thermal or chemical alterations: in the second case the alterations being due to the presence of alkaline conditions. Laser-induced degradation of azurite has been studied as a function of the grain size. The results show that the temperature of the grains decreases as the size increases, and azurite degrades into tenorite only below the critical value of 25 µm. To study the chemical alteration of azurite, the pigment has been applied on the plaster of terracotta samples and analyzed at different pH values by micro-Raman spectroscopy. As opposed to most part of the analytical techniques, it can detect the presence of both azurite and tenorite molecules in the same micro areas, and provides a valuable tool to determine azurite degradation.

The aim of this investigation is to study the changes occurring on the surface of poplar wood exposed to artificial irradiation in a Solar Box. Colour changes were monitored with a reflectance spectrophotometer. Surface chemical modifications were evaluated by measuring the infrared spectra. Hyperspectral imaging was also applied to study the surface wood changes in the visible-near infrared and the short wave infrared wavelength ranges. The data obtained from the different techniques were compared to find the possible correlations in order to evaluate the applicability of the Hyperspectral imaging to investigate wood modifications in a non-invasive modality. The study of colour changes showed an important variation due to photo-irradiation which is the greatest change occurring within the first 24 hours. Infrared spectroscopy revealed that lignin degrades mainly in the first 48 hours. Concerning Hyperspectral imaging, the spectral features in the visible-near infrared range are mainly linked to the spectral shape, whereas in the short wave infrared cellulose and lignin affect shape and reflectance levels. The proposed approach showed that a correlation can be established between colour variation and wood degradation in the visible-near infrared range; furthermore in the short wave infrared region surface chemical changes can be assessed.

Micro-fragments of the painted part of the 'Cembalo' model by Michele Todini (1625-1689) are investigated.The technique used for painting the terracotta base was studied via the stratigraphic analyses. No background layer of inorganic materials, e.g. gypsum, was found. To prevent absorption effects due to the terracotta porosity, a very thin layer of proteinaceous material was probably used. The micro-Raman analyses have revealed the use of pigments currently used in the post-Renaissance period (lead white, indigo, yellow of iron hydroxide, gypsum, hematite and carbon black) mixed with a pigment, the Prussian blue, discovered in A.D. 1704. This raises the authenticity problem of the work of art, a problem analysed and discussed in presenting the history of the work of art, and after the pigment study. The presence of degraded lead white is recognized via the laser-induced degradation of the irradiated material. The possibility of a restoring action of the painted parts, as opposite to the non-originality of the work, is considered and discussed. Since most part of the investigated pigments shows laser-induced effects, a careful study of this phenomenon is performed by using the modern counterparts of the ancient pigments. For different laser powers, the temperatures of the investigated zones have been obtained via the detailed balance principle and connected to the laser-induced degradation effects.

The production of Japanese enamels for porcelain decoration was thought to have originated from the direct and exclusive influence of Chinese potters who moved to Japan during the chaotic Ming to Qing dynastic change in 1644. Recent systematic studies have identified, for the first time, the crucial influence of Jesuit missionaries on pigment and enamel production in Japan from the late 16th-century. In particular, such first encounter laid the foundation for the continued influence exerted by European technology on Japanese art throughout the centuries. The present study has further identified European enamels used for the decoration of polychrome wares fired in Arita, the porcelain production center of Japan. This continued exchange not only marked the Edo period, but also extended into the twentieth century. For the first time, the lack of written records regarding the use of western pigments for enamel production caused by the persecutions of European and Japanese Christians has been overcome in the work herein presented. The nature of the imported materials has been firmly identified and characterized. The analytical results (EDXRF and Raman) have finally revealed how western technology and materials not only kept influencing Japanese art during the isolation (sakoku) period, but also accompanied the strong westernization process that marked Japanese history from the late nineteenth century. Moreover, the significant reverse influence of Japanese-made enamels on Chinese polychrome porcelain production in the late Qing and twentieth century has been fully identified for the first time. Furthermore, results show that the shift of the Pb mode of lead antimonate (Naples Yellow) is affected by the firing temperature for enamel decoration, and that this characteristic, along with the chemical composition, enables the identification of the origin and manufacture period of the yellow enamel.