Light micrograph of a compact disc showing the diffraction of light from the music grooves (top) & plain grooves (colourful bands). The colours are produced by interference between reflected rays of light from adjacent grooves. The disc is made of plastic, which is pressed with a series of fine depressions representing a digitised musical signal capable of being read by a laser. To reflect the laser light, the plastic layer is coated with a metal (aluminium), which follows the depressions exactly. This layer (music layer) is covered by another layer of transparent plastic, which prevents dust & scratches from affecting the sound. Mag:X13 (at 35mm size).