Quartz crystal rheometry: A quantitative technique for studying curing and aging in artists' paints

In this paper we demonstrate the use of a quartz crystal microbalance (QCM) as an effective new tool to measure the physical properties of artists' paints during cure in real time, with unprecedented sensitivity to both mass changes and mechanical properties. While QCM-based dosimeters have been used in the conservation field primarily as mass sensors, the limits of the technique are here extended so that the rheological properties of the materials are obtained as well. The capabilities of the technique are illustrated with alkyd resins, a binder for artists' paints developed in the late 1920s that became widely used in the 1950s. Curing of an alkyd film was monitored both in ambient conditions and at elevated temperatures. By using the QCM as a thin film rheometer, the changes in the film's mass and high-frequency dynamic shear modulus were monitored, and the ability to quantify temperature-dependent changes in the cure rate was demonstrated. The film was also exposed to water and showed slight mass loss but no significant changes in mechanical properties. This work demonstrates that the QCM can be a useful tool for quantifying changes in the mechanical properties of artists' paint films during aging and exposure to different environmental conditions.