Other historic paints, such as distemper or egg tempera, are known to have a short drying phase and to form stiff, brittle films. Alkyd and acrylic paints, since they are modern paints that have been in use for less than 100 years, have also been a strong focus of research efforts in the last few decades. For oil-based paints, the mechanical properties can continue to change over the long periods of time that the curing process is ongoing, motivating active research into the mechanical properties of these paints. As the paint transitions from liquid-like to solid-like, the stiffness of the paint film can typically increase several orders of magnitude. The timescale over which these drying and/or curing processes occur can vary greatly, from a few hours (acrylics) to months (alkyds) to decades (oil-based paints). This transition from liquid- to solid-like behavior can occur two ways: through a drying process, where solvents added to the system evaporate out of the paint film, or through curing, where crosslinking and other chemical reactions occur within the pain film to increase the stiffness. All paint materials have several properties that change over time, initially being a liquid-like film that evolves into a solid-like paint film. Paints are typically comprised of a pigment for coloration, a binding medium, and other additives that can adjust the optical properties and workability of the paint film. It is shown how this area of research has grown and begun to provide possibilities for contributing to improved conservation practices. In the present review our aim is to compile the innovative mechanical testing techniques that have been developed in the last two decades, together with the data derived from these experiments. The most recent review paper discussing the mechanical properties of paint was published thirty years ago, emphasizing the role that temperature (T) and relative humidity (RH) play on brittleness of these films. The mechanical properties play a key role in assessing its stability over the lifetime, providing information about the stiffness, toughness, and the likelihood of crack formation, among other things. A great amount of research has focused on understanding the chemical changes of the curing processes of paints, but they only partially capture the overall stability of a paint film. Paint is a ubiquitous component of art objects and a research subject that has received prominent attention for many years in both industry and cultural heritage. Techniques applied to historic samples incorporate the use of small sample sizes (nanoindentation), optical techniques (laser shearography), computational simulations (finite element analysis), and non-invasive comparative mechanical properties (single-sided nuclear magnetic resonance) to investigate and predict the mechanical properties of paints. Techniques applied to model systems (tensile testing, dynamic mechanic analysis, quartz crystal microbalance, vibration studies) require too large of a sample to be taken from art objects or focus on the mechanical properties of the liquid state (shear rheometry). The techniques have been divided into two categories: those that are restricted to use on model systems and those that are applicable to historic samples. Alongside the more commonly used techniques of tensile testing and dynamic mechanical analysis, new techniques have been developed to more fully investigate the mechanical properties, and are discussed along with salient results. Here, thirty years of tensile testing data have been compiled into a single dataset, along with the testing conditions, to provide future researchers with easy access to these data as well some general discussion of their trends. This response is dependent on many factors, such as paint composition, pigment to binder ratio, temperature, relative humidity, and solvent exposure. The mechanical properties of artists’ paints relate to the deformation response of these materials when a stress is applied. While the chemistry of artists’ paints has previously been studied and reviewed, these studies only capture a portion of the properties affecting the response of paint materials.
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