Component Two: A Study of the Physical Characterization of Modern Paints
The way in which paint films respond to fluctuations of temperature and relative humidity in their environment is governed by their physical properties. Synthetic paint media may expand, soften, and even become slightly sticky upon heating and, conversely, turn extremely brittle at lower temperatures. Such changes in a paint's physical properties may strongly influence phenomena such as rates of soiling, extent of cracking, cupping of its surface, surface texture, color, and gloss. Changes are probably also affected by the presence and nature of pigments and diluting agents, exposure to light, and the age of the material. However, very few measurements have been made on any of the classes of modern paints.

Therefore, an element of this collaborative project is, to develop a more comprehensive understanding of physical properties of modern paints. Research into these phenomena will be conducted utilizing two types of instrumental techniques: thermal analysis and surface characterization.

Thermal analysis instrumentation is a set of tools that provides in-depth information about polymers, plastics, and other organic materials. The most useful thermal analysis techniques for characterizing modern paints are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), and thermogravimetry (TG). Some of the important parameters that can be measured by thermal analysis are glass transition temperature, volatile content, crystallinity, thermal stability, oxidation stability, linear coefficient of thermal expansion, and modulus of elasticity.

Characterization of the surface of paint can be a complex task due to a wide range of parameterssuch as particle size, opacity, and morphologythat affect surface texture, color, and gloss. To document the micro-morphology of paint surfaces, ultra-high resolution images will be obtained using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Color and gloss will be measured with a spectrophotometer that is equipped with an integrating sphere.

Work Completed

Thermomechanical analysis (TMA) was used to measure the thermal properties of freestanding acrylic films before and after aging and subsequent water immersion. In addition to the standard compression measurements, a "film and fiber" attachment was used to characterize the elongation of paint films. In compression mode, glass transition temperature was measured at approximately 3 degrees Celsius for unwashed films, compared to approximately 12 degrees Celsius for films after washing, indicating a significant rise in glass transition after water exposure, which may have important ramifications for crack development and/or dirt pick up in the future. No difference was measured on films before and after aging. In the elongation measurements, an unwashed paint film could be stretched approximately double the distance of a washed film, again indicating the loss of a plasticizing component after water exposure. However, in this mode, a difference on aging could be observed; the increase in elongation for a light-aged film after washing was approximately 50 percent that of the corresponding unaged sample.

Work in Progress

The initial investigations in this component are focused on the development of standard analytical protocols for each measuring instrument that will provide the maximum amount of information on each paint sample tested. Currently, the standard analytical protocols are employed to characterize a number of commercially available artists' acrylic emulsion paints—before and after aging and/or cleaning treatments—and the tests results are shared among the three research partners.

Future Work

The project will adapt the characterization techniques used to develop a similar understanding of other kinds of paint media, such as WMOs, alkyds, nitrocellulose, and vinyl emulsions.

In May 2005, Eric Hagan, Conservation Science Fellow at Tate, initiated a three-year study into the mechanical properties of a variety of modern paints. He will build on the mechanical testing work he carried out on acrylic emulsion paints during his master's degree work at Queens University in Canada, and this research will be submitted for his Ph.D. at Imperial College, London.