oilspot
Oilspot refers to a visual phenomenon observed in certain liquids, most commonly water, where patches of iridescent color appear on the surface. These colors are not due to a pigment within the liquid itself but rather to the optical effect of thin-film interference. When a thin layer of a substance with a different refractive index, such as oil or a similar non-polar liquid, spreads across the surface of a more polar liquid like water, light waves reflect off both the top and bottom surfaces of the thin film.
The thickness of this film, which varies across its surface, causes the reflected light waves to interfere