A methodology for the use of alkyd paint in thermally aged easel painting reconstructions for mechanical testing

Abstract

For the preservation of painted cultural heritage on wooden substrates, it is important to understand the fracture mechanisms in the multilayer system of which they are constructed and how the environment plays a role in the composites’ physical properties. Past research has investigated the material response of each constituent layer but much more needs to be done to represent the heterogeneous composite structure of easel paintings. In recent years fracture mechanics concepts have been applied to glue and glue/chalk multilayers. However, few experiments have been conducted on multilayers that include oil paint, due to its very long, and impractical drying time, which can be a few years up to decades depending on the type of study. The paper presents a methodology for the use of thermally aged alkyd paint in easel painting reconstructions for mechanical testing, specifically as a substitute for naturally aged traditional linseed oil paint. Elastic and failure properties of the paint have been obtained from environmentally-controlled tensile tests on thin free-film samples. To obtain the characteristic properties of increased elastic modulus and reduced ductility, a thermal ageing protocol has been experimentally developed. The results are compared with data from the published literature, theoretical models and with 30-year-old samples of cold-pressed linseed oil lead white paint tested within this research work. The final methodology provides the research community with a viable way to produce samples that can be used to understand the behaviour of a (simplified) but complete multilayer system.