Rheological properties of oil paints and their flow instabilities in blade coating

Painters express their ideas and emotions by making use of oil paints, tools, and painting techniques. Their artworks appear on the surface, which depend on colors, tools, and the sensuous touch of the painters. From the scientific viewpoint, it is determined by the rheological properties of oil paints and their flow behavior while the external force is applied to oil paints. It means that the artists know through learning or by instinct that the oil paints have different rheological properties according to the color, and that various surfaces can be generated by changing the operating conditions. In this study, we measured the rheological properties of oil paints and investigated their flow behavior when the flow was applied. Flow instability was visualized, and the coating window was analyzed, which was supposed to mimic the painting process of the artists. We could understand that oil paints are similar in ingredients, rheological properties, and flow characteristics to industrial coating process. One important thing to note is that the painting is a process to pursue heterogeneity that is generated by the touches of the artists, while the coating process in industry is a process to pursue homogeneity so as to get defect-free surface with high productivity.