There are two basic ways to etch the surface of aluminum to remove the polish- caustic vs acid. Acid is the better, safer and cleaner way to do it. The oven cleaner is caustic. Lye is sodium hydroxide or caustic soda. It will remove a significant amount of surface material- more than acid. It works well at taking away a lot of material, but the residual is hard to deal with and the process is much less safe. In years past, it was the most common way to etch aluminum and to prepare it for anodizing. Acid is much cleaner and safer. A simple water bath will dilute and clean away any residual. The remaining aluminum will sludge to the bottom of your bath. Phosphoric acid is probably the easiest and most readily available. Coca cola has phosphoric acid, so if you leave it in a bath of coke long enough, it will etch the surface. Phosphoric acid can be bought at any home improvement center. TSP works too. Hydroflouric acid is the one more commonly used in industry. However, fluorine is extremely toxic and should be done with good ventilation. Hydrochloric acid will also work, but is the strongest of the three. In any case, you want to work with dilutions and the time the aluminum soaks to get the optimum results. If you are really patient, you can also try vinegar. It will take awhile, but eventually it will etch.
