Colorimetry applied to the field of cultural heritage: examples of study cases

Abstract

For a few years now, the Dipartimento di Storie e Metodi per la Conservazione dei Beni Culturali of the Alma Mater Studiorum Università di Bologna (sede di Ravenna) has been creating a Diagnostic Laboratory for the study on the “system: cultural heritage/conservation environment”. In the present paper the results of different surveys concerning the use of colorimetry on different typologies of art works are reported: graphic documents (fig. 1); oil painting on board and canvas (fig. 2); wall painting (fig. 3); stony materials consolidated with ethyl silicate (fig. 4). Measurements of the chromatic parameters, according to the CIE L*a*b* chromaticity diagram and to the UNI 8941 Standard Coloured surfaces, were carried out with the spectrophotometric colorimeter Minolta CM-2600D model. The reference measurements (targets) were carried out on every typology of works. Such targets, recorded on the tool or in the computer, could be considered in order to draw a comparison in time on the same studied surface. It is then possible to check the trend of the chromatic alteration as an effect of interaction of the environment of location-conservation with the art work and, then to determine the causes, i.e the environmental operating-factors. The measurements of the chromatic parameters for graphic documents and for wall paintings have also allowed us to establish if the modifications, caused by an inappropriate environment, must be linked to irreversible or reversible effects and, then, with the possibility of being removed. As regards wall paintings, the respect of the “noble patina” was showed, as established by the Card of Restoration, by means of the measurement of the + b* parameters (yellow degree). The studies on stony materials aimed at the evaluation of the chromatic alterations of the art works previously consolidated with various products based on ethyl silicates: different results were reached according to the different degree of stone cohesion, anisotropy of the material and different exposure conditions of the works. Such researches may contribute to applying colorimetry in the field of cultural heritage.