AIC's 41st Annual Meeting

Works of art kept in outdoor environments, particularly objects and mural paintings, are vulnerable to deterioration though photodegradation, oxidation, and mechanical abrasion, no matter how well they are treated or maintained. Analysis of art materials using analytical techniques, such as LC-MS, FTIR, terahertz spectroscopy, and SEM-EDX, can help provide an improved understanding of the composition of modern artists' acrylic paints. However, when trying to determine the aging characteristics of outdoor painted artworks, there is difficulty in determining which artificial (accelerated) aging method best corresponds to the real-time outdoor exposure conditions.
Correlation between artificial aging and long-term outdoor urban exposure often lacks fidelity, as photocatalytic reactions are exacerbated in the aging chamber, particularly photooxidation. However, reactions under unpredictable conditions (e.g. weather: freeze/thaw cycling, relative humidity, snow, ice, rain) are not easily mimicked using weatherometers (QUV) or light aging chambers (Atlas xenon arc). The implied advantages of artificial aging in material studies are that the extreme rate of aging and quicker failure can help scientists predict long-term stability and durability of art materials within a reasonable amount of time. Yet a question remains as to how do hours of exposure in an aging chamber match the hours of natural exposure. For example, Philadelphia has an annual average of 62% possible sunshine. Therefore, on a day with 8 possible hours of sunshine, a cultural heritage object might receive only 5 hours of sunlight exposure. How do those 5 hours correlate to 5 hours in the light chamber? Previous research involved artificially and naturally aged UV-protective coatings on artist’s acrylic paints; however, the data collected from the chemical, mechanical, and thermal assessment of these aged samples did not always correspond, as expected. A more recent project involving prepared samples of artists’ acrylic paints may provide a better correlation of artificial aging to natural aging in a Mid-Atlantic environment and help develop modern protocols for replicating natural outdoor exposure in laboratory-based experiments.

In this study, acrylic paint films were naturally and artificially aged and both sample sets were periodically analyzed to determine the different stages of change and deterioration in the surfactant, paint binder, and commonly-used outdoor pigments, and to examine the relationship between the two aging protocols. Environmental conditions (intensity of solar illumination, rainfall, temperature, % RH) were recorded using National Weather Service data. The average environmental conditions were replicated as closely as possible in the weatherometer during artificial aging. It is hoped that this paper can offer improved guidelines for future conservation research projects involving the use of artificial aging of contemporary art materials.