This reminds me of a song: "I'm gonna wash that gray right out of my frame..." This is a simple task that requires a little elbow grease and a soaped steel-wool pad like S.O.S. Dampen the pad in a bucket of warm water and scrub the frames in one direction. You should be sure to wear rubber gloves to protect your hands from the grime produced by the scrubbing. Thoroughly flush the frames with water when you have finished scrubbing. After the frames have dried, put a few drops of light oil (3-in-1 oil is great) onto a soft cloth and rub it onto the aluminum. This provides a new luster and will help to protect them from future oxidation.