The chemicals have "tattooed" the aluminum pores. Almost like an electroless anodizing. Not pretty at all. Too long in the soup, too hot or not enough agitation (or any combination) can cause the stain you describe. The pores are open and absorb the depleted chemical. Normally the aluminum oxide prevents this from happening but while submerged in the chemical etching bath, the oxide is stripped away and the pores laid open.
Soda blasting is probably a good one to try. Do not glass bead or silica blast. The soda (baking soda) is usually quite easy on the surfaces.
BTW, That wonder cleaner was probably laced with sodium hydroxide (lye) In small doses and agitation it can brighten aluminum. Not done right and you now know the rest! Always attend the cleaning. Plenty of brushing about and have plenty of cool clear water on hand!
Some alloys however will darken almost instantly. Alloys with Magnesium seem especially vulnerable . Zing and copper may be as well. Try testing in an inconspicuous area if possible.
Last edited by Jesse Open; 05-17-2018 at 05:08 PM.