The patterns and colors on a soap film/soap bubble, according to the wave theory of light, are due to interference of light from the upper and lower surfaces of the film. Actually a soap film is not a single film but a composite film in which a water film is sandwiched between two layers of oil (present in the soap). As the water film evapourates, the vapour comes out of the oil films by making perforations. The formation of perforations are depicted in the figures Fig-4a1 to Fig-4a5 with Sodium light and Fig-4b1 to Fig-4b4 with white light.
The formation of perforations when illuminated with Mercury Vapour Lamp are depicted in the figures Fig-4b1, Fig-4b2, Fig-4b3 and Fig-4b4.
The formation of perforations as waterfilm evaporates is captured in Video clip-4a.
As the water film is completely evaporated, only the two perforated oil films will be left and as oil film also starts evaporating, the soap film will finally collapse.