Abstract
A thick water film is deposited on a mica substrate, which it wets, from pure water vapour at a low temperature. The vapour pressure is reduced so that the water evaporates. Despite the fact that under equilibrium conditions the film wets the substrate, when it reaches a thickness of about 500 Å, dry patches nucleate in the film and the water recedes to the wet parts. During the recession, a thick rim of water is created, which becomes hydrodynamically unstable and produces a beautiful reproducible pattern of water drops. Experiments have been done showing both homogeneous and heterogeneous nucleation. The basic physics of the de-wetting, the nucleation and the origin of the pattern formation are discussed. The effect is not restricted to water on mica, but has been observed with other fluids on wetted substrates.