This ceramic substrate will not react with oxygen or moisture and is not damaged by temperatures that would significantly warp a conventional plastic optical disc.

FORBES: Storing Information for a Thousand Years

Each disc is covered in a transparent plastic coating (either blue, green, yellow or red) which lets daylight filter through.

WSJ: Daniel Buren's Bright Periphery | 'Excentrique(s) Travail In Situ' at the Grand Palais in Paris

Recently a company from Utah called Millenniata has introduced an optical disc technology utilizing a disc in which the data is etched (or engraved) into a ceramic substrate rather than stamped on plastic like conventional optical discs.

FORBES: Storing Information for a Thousand Years