After you've cast your part it still isn't done. You have the option of finishing it. You can plate it, there is a compound that will remove the oxide layer and give the aluminum another layer for plating it with what ever you wish to plate it with. Copper, bronze, gold, nickel... This zincate layer dissolve when you immerse it in the plating solution. https://caswellplating.com/zincate-8-fl-oz.html You can also polish it up but this won't last long term, and its just clear aluminum. I tried painting some boat items with Kandy paint and it has held up even though the painting method is completely wrong. Polished surface, no primer... Kandy paint if you don't know is a transparent paint. You can anodize it, which I've heard can be splotchy for castings. I haven't anodized castings but I have anodized a few other machined parts. The process is amazingly simple. The only 'difficult' part is you need a quality dye. I suppose if you must you can paint aluminum with regular opaque paint, but...?