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Jan Klaas, Ilaria Van Den Berg, Ester Bonaduce, Ken Ferreira, David Sutherland, Chris Peggie, Maines, Patrick Dietemann, Wibke Neugebauer, Luise Lutz, Cedric Beil, Irene Fiedler (+1 others)
To better understand the painting technique of a given period, information from different sources are usually combined: written statements by the artist or his contemporaries, art technological study of paintings, and chemical analysis. However, does the information obtained from different sources fit together and form an integral picture? Based on a case study of a painting by Arnold Böcklin this question was evaluated. It was found that the correlation between binding media and the properties
more » ... and the properties of paints manufactured from them is not clear and straightforward as is usually believed. To understand these correlations, colloid chemistry is indispensable. This paper presents concepts of a colloidal description of paints consisting of pigment, egg and drying oil. Various methods for the preparation of such paints and their resulting properties are discussed considering aspects of colloid chemistry and rheology, such as stability of emulsions, gel formation, interactions between pigment particles and binders etc. This paper connects a broad variety of information, aspects, models and hypotheses that cannot be discussed in complete detail here. It is intended as a starting point for future discussions and research into various aspects of paints and painting. 1 Introduction As part of a research project into tempera painting around 1900, paintings by Arnold Böcklin (1827-1901) were studied. First, a review of the written sources was conducted followed by a careful technological study of selected paintings. As a third component, cross-sections and samples for binding media analyses were taken from several paintings. Finally, paints were reconstructed based on the information obtained. Thus, data were collected in four ways: written sources, technological study, binding medium analysis and reconstruction of paints. 1 As will be shown below, results obtained from the first three components appeared to completely contradict each other. It seemed that a part of the data was wrong and a uniform interpretation impossible. However, an unexpected solution for the problems encountered was found after consulting recent literature on colloid chemistry and food technology: Paints are colloidal systems and must be treated as such. As a consequence, their properties sometimes differ quite considerably from what is generally expected if the laws of colloid chemistry are disregarded. For example, whether a paint containing both egg and oil as binders can be diluted with water or oil of turpentine depends less on the relative amounts of egg and oil, and more on other factors, as will be discussed below. Paints are colloidal systems-this was obvious at the beginning of the 20 th century, when scientists began to systematically study colloids and their properties, 2,3,4 and books are still being written on this topic today. 5 However, in conservation science the consequences of this concept seem to be mostly forgotten, overlooked or just ignored, although Mayer for example described these aspects very clearly, 6 and important aspects are also mentioned by Gettens and Stout. 7 Fortunately, both colloid chemistry and