When using it on aluminum, no matter how highly polished the surface is, it will turn the surface white. Depending on how fast or slow the surface starts to turn white, or to what degree of whiteness, depends on how much oxidation is on the surface. The faster it turns white, or the whiter the surface gets, the higher the level of oxidation.
When using this product, don’t be afraid of it. In some cases, if the metal is extremely oxidized or if you are dealing with some sort of an acid stain, you may need to totally white-out the surface. By doing this you will find that most hard to clean problems are no longer a problem.
When you get done polishing your aluminum, is it crystal clear? Does it sometimes or all the time have a little bit of a milky film or a milky haze deep underneath the shine? If it does, then you need to use the Aluminum Deoxidizer.
By using the Deoxidizer first to clean the surface, then applying the Purple Metal Polish directly over the top of the Deoxidizer, when you buff the black residue off, your metal will be crystal clear. Highly polished aluminum should look just like chrome.
With so much stuff on the roads these days, the abundance of vehicles along with various chemicals that are sprayed on or near the roadways, it takes a liquid chemical to help clean all that stuff off before you polish.