Disc rot

The reflective layer is typically aluminium, which reacts easily with several commonly encountered chemicals such as oxygen, sulfur,[1] and certain ions carried by liquid water.

This means that a scratch on either surface of a DVD is not as likely to reach the reflective layer and expose it to environmental contamination which can cause corrosion.

Finally, discs made with gold as the reflecting layer are considerably less vulnerable to chemical corrosion problems.

[5][6] Laser rot is the appearance of video and audio artifacts during the playback of LaserDiscs, and their progressive worsening over time.

[4] It is most commonly attributed to oxidation in the aluminum layers by poor quality adhesives used to bond the disc halves together.

Also, in the 1990s, LaserDiscs manufactured by Sony's DADC plant in Terre Haute, Indiana, were plagued by laser rot.