WATCHING PAINT DRY—DOES IT CRACK OR DOES IT WRINKLE?

WATCHING PAINT DRY—DOES IT CRACK OR DOES IT WRINKLE? Perhaps because, as a baseball fan, I am predisposed to take an interest in paint drying, I loved this article by Jonathan Shaw about the applied mathematician Lakshminarayanan Mahadevan. When paint dries, the surface loses liquid faster so that a skin is formed. If more liquid is removed beneath the fixed amount of surface skin, the drop either wrinkles or cracks. If the drop is attached to the surface, it will rip (crack); if the drop is not attached (like a drying grape), it will wrinkle (like a raisin) as the liquid leaving from the inside causes the drop to shrink inside the skin. I had never thought about the why of paint or raisins. Mahadevan uses this as an example to encourage us to wonder about everyday life. The scientists I have known do that. I once took a walk with a physicist who encountered a phenomenon involving the flow of water coming out of a culvert which he could not explain. He spent a happy hour studying and then, as we resumed the walk, puzzling over, the phenomenon.