If you are dealing with powder coat, then only abrasion will work, and it will require something spinning with some force since sand blasting doesn't do much to powder coat in any reasonable amount of time. Once caveat is that some powder coat suppliers sell strippers that supposedly take it right off. I don't have any direct experience with them, so i can't comment on how well they work.
If the surface is anodized, then you are dealing with something more than just a "paint". Anodizing creates porous aluminum oxide on the surface of the part, and actually slightly down into the base metal. Once the part has been anodized, it is rinsed and then stained. The stain will seep into the pores and set. It then has to be rinsed and sealed. After that, you have anodized stain through a thin layer of oxidized aluminum on the surface of the material, and even down into the transition zone where there is a mix of oxidized and non-oxidized aluminum. To take that stuff off, you to remove the entire layer that the stain has penetrated into, which means you are taking away the surface layer of your part.
If you really to have an anodized coating on your parts, then it might be worth it to talk to an anodizing shop to see if they can strip the old stain, clean it up, and then re-anodize it and stain it to whatever color you want (including aluminum/silver). I don't think it will cost as much as you think, and it is SUPER tough. They might also just be able to strip the old stain and give you the piece clean and ready for paint.
Camelman
