CD bronzing is a specific variant of disc rot, a type of corrosion that affects the reflective layer of CDs and renders them unreadable over time. The phenomenon was first reported by John McKelvey in the September/October 1994 issue of American Record Guide.
Affected discs show an uneven brownish discoloring that usually starts at the edge of the disc and slowly works its way toward the center. The top or label layer is affected before the bottom layer. The disc becomes progressively darker over time; tracks at the end of the disc show an increasing number of disc-read errors before becoming unplayable.