In the case of insulating glass made of float glass, interference in the form of spectral colours can occur. Optical interference is the superposition of two or more light waves when they meet at a point. They are shown by more or less strong coloured zones, which change with pressure on the pane. This physical effect is enhanced by the plane parallelism of the glass surfaces. This plane parallelism ensures a distortion-free view. Interference phenomena are random and can not be influenced.