The aluminum base underneath the pan has discolored, and I don’t seem to be able to restore the shiny finish.

Aluminum is a metal that reacts very quickly with chemicals and foods. The best way to prevent the shiny base of SCANPAN from changing color is to carefully prevent food from spilling over the side of the pan. This may not always be practical. But a good scrubbing with a soap filled steel wool pad, such as Brillo® or SOS®, and some concentrated dish washing liquid should restore most, if not all of the shiny finish. Such steel wool pads should be used only on the exterior, shiny aluminum disk. Steel wool pads should not be used on the cooking surface or the outside walls of SCANPAN Cookware.