DiVA - Diagnostic for Valorisation of Artworks
This research line stems from the continued and close collaboration with professionals working in the fields of conservation, restoration, valorization and exploitation of Cultural Heritage goods and has been developed with the goal of applying in an integrated manner some non-destructive diagnostic methods to paintings and other polychrome surfaces. Our activity concerns specifically applications of Raman spectroscopy, both in a fixed version in the laboratory (MRI) and in a mobile version in situ (MRM), as well as colour measurement with the spectrophotometric method (SPC) and with spectroradiometric techniques (SRC).
Determination of Archaeomaterial’s Fingerprint
Signals obtained by Raman spectroscopy, resulting from the anelastic scattering of light incident on the sample, represent a sort of fingerprint of materials and allow the identification of gems and precious stones, of painter’s pigments and of possible deterioration products, by comparison of the experimental spectrum detected from the examined sample with Raman spectra of the database. This technique is one of the best analysis methods for the characterization of pigments of ancient artefacts thanks to the following features, all indispensable to study artworks: good sensitivity and spatial resolution, non-destructiveness and possibility to perform the measurement in situ. In a first phase the goal of our research work was the construction of a database of Raman spectra of the pigments most frequently used for the realization of paintings. This is the so-called ColoRaman project, which aimed to construct a database of spectra, both Raman and fluorescence, obtained with different excitation laser sources (green, red, IR), of pigments both pure and deployed with different ligands (oil, casein, egg tempera) on different backings (canvas, wood, frescos). Special attention was devoted to historical pigments, meaning those used most by artists in the past. Similar goals has the CeRaman projects, which aims to construct a similar database using ceramics samples, prepared with the most common production and decoration techniques, with special attention on the effects of the latter on the experimental spectrum.
Our current research in the field of paintings aims to solve problems originating from the artist’s common practice of realizing spreads by mixing pigments on their palette. The possibility to identify the pigments used for these composites depends on the capabilities of Raman spectroscopy to identify the elements included in the mix. Results obtained so far show a dependence on the measurement experimental parameters and the need of appropriate computing techniques for the analysis of the obtained spectra.
Colorimetry for the Arts
Colour is the top interest for those who deal with research applied to artworks, be it for pure knowledge or for conservation purposes, especially in the case of paintings of polychrome pieces. The same is true for the authorities whose duty is studying artworks with the goal of conserving it and making it available for public enjoyment. Measurements on a painting aim to determine the artist’s palette, to setup conservation plans, to find the possible causes of deterioration, and to perform pre– and post-restoration diagnoses, in order to assess the effects of a restoration project in terms of colour variations. We have performed colorimetric measurement campaigns on frescos in several Churches of the Caltanissetta and Siracusa districts, on paintings by Mario Minniti and other disciples of Caravaggio, canvas and woods subjected to specific restoration projects.
In the last few years, there has been growing interest for techniques which would allow to specify colour in a unique way, expressing it in an international standards system, and thus to specify also the colour differences with respect to a reference point. This has become a top research topic for our LDL&BBCC laboratory, whose researchers are members of the Italian National Colour’s Group and collaborate with the leading experts, both nationally and internationally, in the field. Initially, we realized a series of measurements with the spectrophotometric method, then we have performed measurements for quantitative evaluation of light distribution and measurements of spectroradiometric quantities both for the characterization of the light sources and for the specification of the colour. Our researches are performed with very clear objectives, the chief one being setting up a protocol for colorimetric measurement both close-in and remote (determination of the chromatic coordinates and the behaviour of the spectral reflectance factor), which would allow normalization of all possible experimental conditions with special attention on the calibration procedures. A further objective has been the determination of a precise reference value for the evaluation of colour differences in the field of conservation and restoration of polychrome surfaces. To this end we started a statistical study which, after selection of a suitable class of samples, should allow to setup a test aimed to correlate the different measured values to the chromatic variation detected in the sample. We are also realizing a set of measurements on test spreads created on purpose, in order to investigate the capabilities of spectrophotometric and spectroradiometric techniques for the identification of the pigments and to correlate the obtained data with some of the features of the investigated painting stratum. In this respect, goal of our research is the realization of a detailed study of the diffused reflectance physical phenomenon, with specific reference to its dependence on the geometrical measurement conditions, on experimental parameters, on the ligand used for the spread and on the granulometry of the pigment (Figure 2).
Sebastiano Olindo Troja