The "Forever" Format That Wasn't
When Compact Discs launched in 1982, they were marketed as "Perfect Sound Forever." Because the laser never physically touches the disc (unlike a vinyl needle), engineers assumed they would last indefinitely. They failed to account for chemistry.
A disc is a sandwich: a polycarbonate plastic substrate, a reflective metal layer, and a protective lacquer. Disc Rot occurs when air penetrates the lacquer and eats the metal. On a CD-R, it occurs when the organic dye (which holds the data) naturally fades from UV exposure.
Visual Diagnostics
Archaeologists identify Disc Rot by holding the artifact up to a strong light source:
1. Pinholes
Tiny dots of light visible through the disc. This means the aluminum has oxidized and fallen away. The data in those sectors is gone forever.
2. Bronzing
The disc turns a golden-brown color. This is specific to discs manufactured by Philips and Dupont Optical (PDO) in the late 80s and early 90s, caused by the sulfur in the paper booklets reacting with the silver reflective layer.
3. Laser Rot
A specific term for LaserDiscs, where the glue holding the two sides together fails, creating "snow" in the video playback.
Field Notes
The "Gold" Standard: Archival grade CD-Rs use gold instead of aluminum for the reflective layer because gold does not oxidize. However, the organic dye still decays. Even the most expensive "Archival Gold" disc has a lifespan of ~100 years in perfect conditions—a blink of an eye in archaeological terms.
The Sega Saturn Crisis: Certain batches of Sega Saturn games (mid-90s) are notorious for "bit rot" (actually disc rot). Collectors hold these discs up to the light in terror, searching for the tell-tale pinholes that turn a $500 game into a coaster.