THE LEVELING OF PAINT FILMS

Using a brush to apply paint to a flat surface almost inevitably means that the bristles of the brush leave behind an uneven paint surface. As the paint dries out, these non-uniformities tend to flatten out to leave a protective and aesthetically pleasing even coating; however, e xperiments have shown that some solvent-based high-gloss alkyd paints can exhibit more unusual behaviour as they dry. In these experiments t he initial rate of levelling was faster than that expected simply due to constant surface tension effects, and, much more unexpectedly, over a timescale of a few minutes the peaks of the original disturbance be came troughs and vice versa. In this paper the author presents a mathe matical model for the drying of a layer of solvent-based high-gloss al kyd paint and analyses the linear stability of a uniform layer of pain t subject to an initial perturbation representing the marks left by a paint brush. Investigating the model highlights the crucial role playe d by solvent evaporation and leads to a plausible physical explanation of the observed phenomena. Furthermore, the analytical and numerical predictions of the model are found to be in good quantitative agreemen t with the experimental results.