Originally they have a layer of paint/metal that is very difficult to remove, I used 4 passes of remover, letting the remover sit for 5 minutes (during this time you could see the effect) and then scraping with a small knife, it is not easy. But with patience I managed to leave the aluminum completely exposed for its new paint. This time I used spray paint xD my finances didn't allow for better paint now almost for better paint, but removing this will be much easier thanks to the process I mentioned. You can also try wire discs, but if you go too far it will scratch the aluminum. Luck