Optical Characterisation of Oil Painting Films with Drying Pigments under the Microscope: Cobalt Blue

[EN] Traditionally, oil painting techniques have used certain additives to improve and adjust the rheological characteristics and properties of oil paints. In addition to the main components of oil paints, such as pigments and oils, additives have been used, among which driers, mainly composed of metallic salts such as lead, zinc, cobalt, manganese, copper or iron, play a crucial role in accelerating the drying process of the paint. This paper focuses on the study of oil paint films made with cobalt blue pigment. The main objective is to observe and characterise this pigment using various non-invasive techniques. Specifically, it focuses on the microscopic observation of mock-ups made with cobalt blue in order to detect possible changes in the morphology of different pigments caused by accelerated ageing. This article aims to complement the characterisation of these mock-ups by colorimetry, the results of which were presented at the XVIII Conferenza del Colore in Lecco, 2023 (Llácer Peiró et al., 2023).