Each mother typically makes 3-6 negative metal impressions called sons or stampers. The sons are suitable as molds for injection molding. Polycarbonate is used to injection mold the CD disks. Once the disks are molded, a metal layer is used to coat the disks. Aluminum, gold, copper and silver are all reflective enough to be optically acceptable.
Gold is typically too expensive and copper has a peculiar appearance.
Thus, aluminum and silver are the most commonly used metals. Finally, the logo and other information is silk screened on the top.