Exploring

Inherent Vice: Optical Media

CD/DVD Substrate

Damage caused by the adhesive on a barcode has rendered this bootleg video CD useless.
Courtesy of Stanford University Libraries

Both CDs and DVDs have a polycarbonate (clear plastic) substrate (CDs have one layer, while DVDs have two layers joined with adhesive). This stabilizes the disc, keeping it flat, and provides the depth necessary for the laser to focus on the data layer and the metal reflective layer. Thus, in a CD, which is read by the laser from the bottom, the data layer is actually near the top of the disc. In a DVD, the data layers are better protected due to the presence of a polycarbonate layer on both sides of the disc.

Characteristic Types of Deterioration

Although the polycarbonate will deteriorate over time, the other elements within a disc (e.g., the data layer or the metal reflective layer) will deteriorate more quickly. The polycarbonate layer is vulnerable to poor handling, however. Fingerprints, smudges, scratches, particles of dirt or dust, solvents, or excessive moisture all may interfere with the ability of the laser to read the data layer.

Optical discs are also vulnerable to problems with disc integrity, including separation of the layers, warping, cracking of the layers, and pinholes. These problems are made worse by exposure to high temperature, humidity and extreme fluctuations in climate.