Part of the fluid layer close to the surface gets pressed against the surface, giving rise to a distinct fringe pattern due to strong surface potentials. The pattern depends on the nature of the surface and thickness of material.
The pattern on the surface of the coverslip is shown in Fig-2a, Fig-2b with Sodium and white light respectively. The same pattern is witnessed with polythene sheet as shown in Fig-2c, Fig-2d, In respect of films of liquids like water and oil also similar surface pattern is seen. This is responsible for colours and pattern on oil slick and water film. Depending on the thickness of oil slick, Newton's rings, distorted Newton's rings, broad bands of pattern are formed.
Above the surface pattern, still a portion of the fluid layer exists. This portion of fluid layer in combination with fluid layers of other surfaces gives rise to complex fluid and related fringe pattern. In the Fig-2e and Fig-2f below a lens is placed over a thin glass foil whereby the complex fluid pattern is seen above the surface pattern of the foil with Sodium light and white light respectively.
Surface Pattern on a water drop
The change in Surface Pattern as water evaporates on a water drop is shown below.