All optical media are prepared using the same procedure. The substrate is the clear plastic layer that forms the bulk of the disc. A thin layer of dye is placed above the plastic. This is where the laser records data in the form of burned or clear spots. The dye, which is commonly made of Cyanine or a compound thereof, changes its optical properties under the laser beam. In the case of pre-manufactured CDs, the pattern of pits and lands are stamped on the substrate itself. A reflective film, usually made of silver or gold, comes next. Finally, a protective acrylic coat is applied. Additionally, a layer for labelling purposes is added. In case of dual-layer media, there are two layers of dye with a layer of semi-reflective material in between them.