Field of the Invention This invention relates to an alkaline blast cleaning system for aluminum surfaces which minimizes or eliminates discoloring or tarnishing of the aluminum sur faces. The invention further relates to processes for using the system in cleaning aluminum surfaces without causing significant discoloring or tarnishing of the aluminum. More specifically, the invention concerns the use of small amounts of an alkali metal silicate, preferably sodium silicate, in conjunction with alkali metal bicarbonates, particularly sodium bicarbonate, in blast cleaning systems to substantially reduce or altogether prevent alkali attack on aluminum, particularly aircraft aluminum. The present invention also particularly reates to an improved method for cleaning or stripping paint from the exterior surface of aircraft by blasting sodium bicarbonate inhibited with sodium silicate against the aircraft's exterior surfaces.