[xattt]

Stamped = Data pits are a physical, unalterable thing on the disc. CD-R = Pits are still physical, but they are on a die layer that can fade. Some discs are more resilient (blue, gold) than others (cyan). CD-RW = Pits are (mostly) bistable for practical purposes, but will degrade to a neutral state on a long-term basis.

[bityard]

"Unalterable" is a matter of some debate... The physical pits and lands are on a super thin layer of aluminum. Ideally, this is protected with a laquer coating, but a lot of CD manufacturers in the 90s and 00s skimped on this to save money. I owned a lot of CDs where the coating didn't hold up over time and the aluminum just sort of flaked off, or became damaged/scratched easier than they should have with normal handling.